bionic (3) Tcl_GetChangeTimeFromStat.3tcl.gz

Provided by: tcl8.5-doc_8.5.19-4_all bug

NAME

       Tcl_FSRegister,         Tcl_FSUnregister,         Tcl_FSData,         Tcl_FSMountsChanged,
       Tcl_FSGetFileSystemForPath,   Tcl_FSGetPathType,   Tcl_FSCopyFile,    Tcl_FSCopyDirectory,
       Tcl_FSCreateDirectory,    Tcl_FSDeleteFile,    Tcl_FSRemoveDirectory,    Tcl_FSRenameFile,
       Tcl_FSListVolumes,        Tcl_FSEvalFile,        Tcl_FSEvalFileEx,         Tcl_FSLoadFile,
       Tcl_FSMatchInDirectory,    Tcl_FSLink,   Tcl_FSLstat,   Tcl_FSUtime,   Tcl_FSFileAttrsGet,
       Tcl_FSFileAttrsSet,        Tcl_FSFileAttrStrings,        Tcl_FSStat,         Tcl_FSAccess,
       Tcl_FSOpenFileChannel,  Tcl_FSGetCwd,  Tcl_FSChdir,  Tcl_FSPathSeparator,  Tcl_FSJoinPath,
       Tcl_FSSplitPath,     Tcl_FSEqualPaths,     Tcl_FSGetNormalizedPath,      Tcl_FSJoinToPath,
       Tcl_FSConvertToPathType,           Tcl_FSGetInternalRep,          Tcl_FSGetTranslatedPath,
       Tcl_FSGetTranslatedStringPath,          Tcl_FSNewNativePath,          Tcl_FSGetNativePath,
       Tcl_FSFileSystemInfo, Tcl_AllocStatBuf - procedures to interact with any filesystem

SYNOPSIS

       #include <tcl.h>

       int
       Tcl_FSRegister(clientData, fsPtr)

       int
       Tcl_FSUnregister(fsPtr)

       ClientData
       Tcl_FSData(fsPtr)

       void
       Tcl_FSMountsChanged(fsPtr)

       Tcl_Filesystem*
       Tcl_FSGetFileSystemForPath(pathPtr)

       Tcl_PathType
       Tcl_FSGetPathType(pathPtr)

       int
       Tcl_FSCopyFile(srcPathPtr, destPathPtr)

       int
       Tcl_FSCopyDirectory(srcPathPtr, destPathPtr, errorPtr)

       int
       Tcl_FSCreateDirectory(pathPtr)

       int
       Tcl_FSDeleteFile(pathPtr)

       int
       Tcl_FSRemoveDirectory(pathPtr, int recursive, errorPtr)

       int
       Tcl_FSRenameFile(srcPathPtr, destPathPtr)

       Tcl_Obj*
       Tcl_FSListVolumes(void)

       int                                                                                        │
       Tcl_FSEvalFileEx(interp, pathPtr, encodingName)                                            │

       int
       Tcl_FSEvalFile(interp, pathPtr)

       int
       Tcl_FSLoadFile(interp, pathPtr, sym1, sym2, proc1Ptr, proc2Ptr,
                      handlePtr, unloadProcPtr)

       int
       Tcl_FSMatchInDirectory(interp, resultPtr, pathPtr, pattern, types)

       Tcl_Obj*
       Tcl_FSLink(linkNamePtr, toPtr, linkAction)

       int
       Tcl_FSLstat(pathPtr, statPtr)

       int
       Tcl_FSUtime(pathPtr, tval)

       int
       Tcl_FSFileAttrsGet(interp, int index, pathPtr, objPtrRef)

       int
       Tcl_FSFileAttrsSet(interp, int index, pathPtr, Tcl_Obj *objPtr)

       const char**
       Tcl_FSFileAttrStrings(pathPtr, objPtrRef)

       int
       Tcl_FSStat(pathPtr, statPtr)

       int
       Tcl_FSAccess(pathPtr, mode)

       Tcl_Channel
       Tcl_FSOpenFileChannel(interp, pathPtr, modeString, permissions)

       Tcl_Obj*
       Tcl_FSGetCwd(interp)

       int
       Tcl_FSChdir(pathPtr)

       Tcl_Obj*
       Tcl_FSPathSeparator(pathPtr)

       Tcl_Obj*
       Tcl_FSJoinPath(listObj, elements)

       Tcl_Obj*
       Tcl_FSSplitPath(pathPtr, lenPtr)

       int
       Tcl_FSEqualPaths(firstPtr, secondPtr)

       Tcl_Obj*
       Tcl_FSGetNormalizedPath(interp, pathPtr)

       Tcl_Obj*
       Tcl_FSJoinToPath(basePtr, objc, objv)

       int
       Tcl_FSConvertToPathType(interp, pathPtr)

       ClientData
       Tcl_FSGetInternalRep(pathPtr, fsPtr)

       Tcl_Obj *
       Tcl_FSGetTranslatedPath(interp, pathPtr)

       const char *
       Tcl_FSGetTranslatedStringPath(interp, pathPtr)

       Tcl_Obj*
       Tcl_FSNewNativePath(fsPtr, clientData)

       const char *
       Tcl_FSGetNativePath(pathPtr)

       Tcl_Obj*
       Tcl_FSFileSystemInfo(pathPtr)

       Tcl_StatBuf*
       Tcl_AllocStatBuf()

ARGUMENTS

       Tcl_Filesystem *fsPtr (in)                         Points  to  a  structure containing the
                                                          addresses of  procedures  that  can  be
                                                          called    to    perform   the   various
                                                          filesystem operations.

       Tcl_Obj *pathPtr (in)                              The path represented by this object  is
                                                          used for the operation in question.  If
                                                          the object does  not  already  have  an
                                                          internal  path  representation, it will
                                                          be converted to have one.

       Tcl_Obj *srcPathPtr (in)                           As for pathPtr, but used for the source
                                                          file for a copy or rename operation.

       Tcl_Obj *destPathPtr (in)                          As   for  pathPtr,  but  used  for  the
                                                          destination  filename  for  a  copy  or
                                                          rename operation.

       const char *encodingName (in)                      The  encoding of the data stored in the
                                                          file identified by pathPtr  and  to  be
                                                          evaluated.

       const char *pattern (in)                           Only files or directories matching this
                                                          pattern will be returned.

       Tcl_GlobTypeData *types (in)                       Only files or directories matching  the
                                                          type  descriptions  contained  in  this
                                                          structure  will  be   returned.    This
                                                          parameter may be NULL.

       Tcl_Interp *interp (in)                            Interpreter  to use either for results,
                                                          evaluation,    or    reporting    error
                                                          messages.

       ClientData clientData (in)                         The  native  description  of  the  path
                                                          object to create.

       Tcl_Obj *firstPtr (in)                             The  first  of  two  path  objects   to
                                                          compare.   The  object may be converted
                                                          to path type.

       Tcl_Obj *secondPtr (in)                            The  second  of  two  path  objects  to
                                                          compare.   The  object may be converted
                                                          to path type.

       Tcl_Obj *listObj (in)                              The list of path elements to operate on
                                                          with a join operation.

       int elements (in)                                  If non-negative, the number of elements
                                                          in the listObj which should  be  joined
                                                          together.    If   negative,   then  all
                                                          elements are joined.

       Tcl_Obj **errorPtr (out)                           In the case of an error, filled with an
                                                          object  containing the name of the file
                                                          which caused an error  in  the  various
                                                          copy/rename operations.

       Tcl_Obj **objPtrRef (out)                          Filled  with  an  object containing the
                                                          result of the operation.

       Tcl_Obj *resultPtr (out)                           Pre-allocated object in which to  store
                                                          (using   Tcl_ListObjAppendElement)  the
                                                          list of files or directories which  are
                                                          successfully matched.

       int mode (in)                                      Mask consisting of one or more of R_OK,
                                                          W_OK, X_OK and F_OK.   R_OK,  W_OK  and
                                                          X_OK  request checking whether the file
                                                          exists  and   has   read,   write   and
                                                          execute    permissions,   respectively.
                                                          F_OK just  requests  checking  for  the
                                                          existence of the file.

       Tcl_StatBuf *statPtr (out)                         The  structure that contains the result
                                                          of a stat or lstat operation.

       const char *sym1 (in)                              Name of a procedure to look up  in  the
                                                          file's symbol table

       const char *sym2 (in)                              Name  of  a procedure to look up in the
                                                          file's symbol table

       Tcl_PackageInitProc **proc1Ptr (out)               Filled with the init function for  this
                                                          code.

       Tcl_PackageInitProc **proc2Ptr (out)               Filled  with the safe-init function for
                                                          this code.

       ClientData *clientDataPtr (out)                    Filled with  the  clientData  value  to
                                                          pass  to  this  code's  unload function
                                                          when it is called.

       Tcl_LoadHandle *handlePtr (out)                    Filled   with   an    abstract    token
                                                          representing the loaded file.

       Tcl_FSUnloadFileProc **unloadProcPtr (out)         Filled  with  the  function  to  use to
                                                          unload this piece of code.

       utimbuf *tval (in)                                 The access and  modification  times  in
                                                          this structure are read and used to set
                                                          those values for a given file.

       const char *modeString (in)                        Specifies  how  the  file  is   to   be
                                                          accessed.   May  have any of the values
                                                          allowed for the mode  argument  to  the
                                                          Tcl open command.

       int permissions (in)                               POSIX-style  permission  flags  such as
                                                          0644.  If a new file is created,  these
                                                          permissions  will be set on the created
                                                          file.

       int *lenPtr (out)                                  If non-NULL, filled with the number  of
                                                          elements in the split path.

       Tcl_Obj *basePtr (in)                              The  base  path on to which to join the
                                                          given elements.  May be NULL.

       int objc (in)                                      The number of elements in objv.

       Tcl_Obj *const objv[] (in)                         The elements to join to the given  base
                                                          path.

       Tcl_Obj *linkNamePtr (in)                          The  name  of the link to be created or
                                                          read.

       Tcl_Obj *toPtr (in)                                What the link called linkNamePtr should
                                                          be  linked  to, or NULL if the symbolic
                                                          link specified by linkNamePtr is to  be
                                                          read.

       int linkAction (in)                                OR-ed  combination  of flags indicating
                                                          what kind of  link  should  be  created
                                                          (will  be  ignored  if  toPtr is NULL).
                                                          Valid     bits     to      set      are
                                                          TCL_CREATE_SYMBOLIC_LINK            and
                                                          TCL_CREATE_HARD_LINK.  When both  flags
                                                          are  set  and the underlying filesystem
                                                          can  do  either,  symbolic  links   are
                                                          preferred.
_________________________________________________________________________________________________

DESCRIPTION

       There  are  several  reasons  for  calling the Tcl_FS API functions (e.g. Tcl_FSAccess and
       Tcl_FSStat) rather than calling system level functions  like  access  and  stat  directly.
       First,  they  will  work  cross-platform,  so  an  extension  which calls them should work
       unmodified on Unix and Windows.  Second, the  Windows  implementation  of  some  of  these
       functions  fixes  some  bugs  in the system level calls.  Third, these function calls deal
       with any “Utf to platform-native” path conversions which may be required  (and  may  cache
       the  results of such conversions for greater efficiency on subsequent calls).  Fourth, and
       perhaps most importantly, all of these functions  are  “virtual  filesystem  aware”.   Any
       virtual  filesystem (VFS for short) which has been registered (through Tcl_FSRegister) may
       reroute file access to alternative media or access methods.  This means that all of  these
       functions  (and therefore the corresponding file, glob, pwd, cd, open, etc.  Tcl commands)
       may be operate on “files” which are not native files in the native filesystem.  This  also
       means that any Tcl extension which accesses the filesystem (FS for short) through this API
       is automatically “virtual filesystem aware”.  Of course,  if  an  extension  accesses  the
       native  filesystem directly (through platform-specific APIs, for example), then Tcl cannot
       intercept such calls.

       If appropriate VFSes have been registered, the “files”  may,  to  give  two  examples,  be
       remote  (e.g.  situated  on  a  remote  ftp  server) or archived (e.g. lying inside a .zip
       archive).  Such registered filesystems provide a lookup table of  functions  to  implement
       all  or  some  of  the functionality listed here.  Finally, the Tcl_FSStat and Tcl_FSLstat
       calls abstract away from what the  “struct  stat”  buffer  is  actually  declared  to  be,
       allowing  the  same  code  to be used both on systems with and systems without support for
       files larger than 2GB in size.

       The Tcl_FS API is objectified and may  cache  internal  representations  and  other  path-
       related strings (e.g. the current working directory).  One side-effect of this is that one
       must not pass in objects with a reference count of zero to any  of  these  functions.   If
       such  calls were handled, they might result in memory leaks (under some circumstances, the
       filesystem code may wish to retain a reference to the passed in object, and  so  one  must
       not assume that after any of these calls return, the object still has a reference count of
       zero - it may have been incremented) or in a direct segmentation fault  (or  other  memory
       access  error)  due  to  the  object  being  freed  part  way  through  the complex object
       manipulation required to ensure that  the  path  is  fully  normalized  and  absolute  for
       filesystem determination.  The practical lesson to learn from this is that
              Tcl_Obj *path = Tcl_NewStringObj(...);
              Tcl_FSWhatever(path);
              Tcl_DecrRefCount(path);
       is  wrong, and may cause memory errors. The path must have its reference count incremented
       before passing it in, or decrementing it.  For this reason, objects with a reference count
       of  zero  are  considered  not  to  be  valid  filesystem paths and calling any Tcl_FS API
       function with such an object will result in no action being taken.

   FS API FUNCTIONS
       Tcl_FSCopyFile attempts to copy the file given by srcPathPtr to the  path  name  given  by
       destPathPtr.    If  the  two  paths  given  lie  in  the  same  filesystem  (according  to
       Tcl_FSGetFileSystemForPath) then that filesystem's “copy file” function is called  (if  it
       is  non-NULL).   Otherwise the function returns -1 and sets the errno global C variable to
       the “EXDEV” POSIX error code (which signifies a “cross-domain link”).

       Tcl_FSCopyDirectory attempts to copy the directory given by srcPathPtr to  the  path  name
       given  by  destPathPtr.   If  the two paths given lie in the same filesystem (according to
       Tcl_FSGetFileSystemForPath) then that filesystem's “copy file” function is called  (if  it
       is  non-NULL).   Otherwise the function returns -1 and sets the errno global C variable to
       the “EXDEV” POSIX error code (which signifies a “cross-domain link”).

       Tcl_FSCreateDirectory attempts to create the directory given by  pathPtr  by  calling  the
       owning filesystem's “create directory” function.

       Tcl_FSDeleteFile  attempts  to  delete  the  file  given  by pathPtr by calling the owning
       filesystem's “delete file” function.

       Tcl_FSRemoveDirectory attempts to remove the directory given by  pathPtr  by  calling  the
       owning filesystem's “remove directory” function.

       Tcl_FSRenameFile  attempts to rename the file or directory given by srcPathPtr to the path
       name given by destPathPtr.  If the two paths given lie in the same  filesystem  (according
       to Tcl_FSGetFileSystemForPath) then that filesystem's “rename file” function is called (if
       it is non-NULL).  Otherwise the function returns -1 and sets the errno global  C  variable
       to the “EXDEV” POSIX error code (which signifies a “cross-domain link”).

       Tcl_FSListVolumes  calls  each filesystem which has a non-NULL “list volumes” function and
       asks them to return their list of root volumes.  It accumulates the  return  values  in  a
       list which is returned to the caller (with a reference count of 0).

       Tcl_FSEvalFileEx  reads  the  file  given  by  pathPtr  using  the  encoding identified by │
       encodingName and evaluates its contents as a Tcl script.  It returns the same  information │
       as  Tcl_EvalObjEx.   If  encodingName is NULL, the system encoding is used for reading the │
       file contents.  If the file could not be read then a Tcl error is returned to describe why │
       the  file  could  not be read.  The eofchar for files is “\32” (^Z) for all platforms.  If │
       you require a “^Z” in code for string comparison, you can use “\032”  or  “\u001a”,  which │
       will  be safely substituted by the Tcl interpreter into “^Z”.  Tcl_FSEvalFile is a simpler │
       version of Tcl_FSEvalFileEx that always uses the system encoding when reading the file.

       Tcl_FSLoadFile dynamically loads a binary code file into memory and returns the  addresses
       of two procedures within that file, if they are defined.  The appropriate function for the
       filesystem to which pathPtr belongs will be called.  If that filesystem does not implement
       this function (most virtual filesystems will not, because of OS limitations in dynamically
       loading binary code), Tcl will attempt to copy the file to a temporary directory and  load
       that temporary file.

       Returns  a  standard Tcl completion code.  If an error occurs, an error message is left in
       the interp's result.

       Tcl_FSMatchInDirectory is used by the globbing code to search a directory  for  all  files
       which match a given pattern.  The appropriate function for the filesystem to which pathPtr
       belongs will be called.

       The return value is a  standard  Tcl  result  indicating  whether  an  error  occurred  in
       globbing.   Error messages are placed in interp (unless interp is NULL, which is allowed),
       but good results are placed in the resultPtr given.

       Note that the glob code implements recursive patterns internally, so  this  function  will
       only ever be passed simple patterns, which can be matched using the logic of string match.
       To handle recursion, Tcl will call this function frequently asking only for directories to
       be  returned.   A special case of being called with a NULL pattern indicates that the path
       needs to be checked only for the correct type.

       Tcl_FSLink replaces the library version  of  readlink,  and  extends  it  to  support  the
       creation  of  links.   The  appropriate  function  for the filesystem to which linkNamePtr
       belongs will be called.

       If the toPtr is NULL, a “read  link”  action  is  performed.   The  result  is  a  Tcl_Obj
       specifying  the  contents  of  the symbolic link given by linkNamePtr, or NULL if the link
       could not be read.  The result is owned by the caller, which should call  Tcl_DecrRefCount
       when  the  result is no longer needed.  If the toPtr is not NULL, Tcl should create a link
       of one of the types passed in in the linkAction flag.  This flag is an ORed combination of
       TCL_CREATE_SYMBOLIC_LINK  and TCL_CREATE_HARD_LINK.  Where a choice exists (i.e. more than
       one flag is passed in), the Tcl convention is to prefer symbolic links.  When  a  link  is
       successfully  created,  the return value should be toPtr (which is therefore already owned
       by the caller).  If unsuccessful, NULL is returned.

       Tcl_FSLstat fills the stat structure statPtr with information about  the  specified  file.
       You  do not need any access rights to the file to get this information but you need search
       rights to all directories named in the path leading  to  the  file.   The  stat  structure
       includes info regarding device, inode (always 0 on Windows), privilege mode, nlink (always
       1 on Windows), user id (always 0 on Windows), group id (always 0 on Windows),  rdev  (same
       as  device  on Windows), size, last access time, last modification time, and last metadata
       change time.

       If path exists, Tcl_FSLstat returns  0  and  the  stat  structure  is  filled  with  data.
       Otherwise, -1 is returned, and no stat info is given.

       Tcl_FSUtime replaces the library version of utime.

       This  returns  0  on  success  and  -1  on  error  (as  per  the utime documentation).  If
       successful, the function will update the “atime” and “mtime” values of the file given.

       Tcl_FSFileAttrsGet implements read access for the  hookable  file  attributes  subcommand.
       The appropriate function for the filesystem to which pathPtr belongs will be called.

       If  the  result  is  TCL_OK,  then  an  object was placed in objPtrRef, which will only be
       temporarily valid (unless Tcl_IncrRefCount is called).

       Tcl_FSFileAttrsSet implements write access for the hookable  file  attributes  subcommand.
       The appropriate function for the filesystem to which pathPtr belongs will be called.

       Tcl_FSFileAttrStrings  implements  part  of  the hookable file attributes subcommand.  The
       appropriate function for the filesystem to which pathPtr belongs will be called.

       The called procedure may either return an array of strings, or may instead return NULL and
       place  a  Tcl  list into the given objPtrRef.  Tcl will take that list and first increment
       its reference count before using it.  On completion of that use, Tcl  will  decrement  its
       reference count.  Hence if the list should be disposed of by Tcl when done, it should have
       a reference count of zero, and if the list should  not  be  disposed  of,  the  filesystem
       should ensure it retains a reference count to the object.

       Tcl_FSAccess  checks  whether  the  process  would  be  allowed to read, write or test for
       existence of the file (or other filesystem object) whose name is pathname.    If  pathname
       is  a  symbolic  link on Unix, then permissions of the file referred by this symbolic link
       are tested.

       On success (all requested permissions granted), zero is returned.  On error (at least  one
       bit  in  mode  asked for a permission that is denied, or some other error occurred), -1 is
       returned.

       Tcl_FSStat fills the stat structure statPtr with information  about  the  specified  file.
       You  do not need any access rights to the file to get this information but you need search
       rights to all directories named in the path leading  to  the  file.   The  stat  structure
       includes info regarding device, inode (always 0 on Windows), privilege mode, nlink (always
       1 on Windows), user id (always 0 on Windows), group id (always 0 on Windows),  rdev  (same
       as  device  on Windows), size, last access time, last modification time, and last metadata
       change time.

       If path exists, Tcl_FSStat  returns  0  and  the  stat  structure  is  filled  with  data.
       Otherwise, -1 is returned, and no stat info is given.

       Tcl_FSOpenFileChannel  opens a file specified by pathPtr and returns a channel handle that
       can be used to perform input and output on the file. This API is modeled after  the  fopen
       procedure  of  the  Unix standard I/O library.  The syntax and meaning of all arguments is
       similar to those given in the Tcl open command when opening a file.  If  an  error  occurs
       while  opening  the  channel, Tcl_FSOpenFileChannel returns NULL and records a POSIX error
       code that can be retrieved  with  Tcl_GetErrno.   In  addition,  if  interp  is  non-NULL,
       Tcl_FSOpenFileChannel leaves an error message in interp's result after any error.

       The  newly  created channel is not registered in the supplied interpreter; to register it,
       use Tcl_RegisterChannel.  If one of the standard channels, stdin,  stdout  or  stderr  was
       previously  closed,  the  act of creating the new channel also assigns it as a replacement
       for the standard channel.

       Tcl_FSGetCwd replaces the library version of getcwd.

       It returns the Tcl library's current working directory.  This  may  be  different  to  the
       native  platform's  working directory, which happens when the current working directory is
       not in the native filesystem.

       The result is a pointer to a Tcl_Obj specifying the current  directory,  or  NULL  if  the
       current  directory could not be determined.  If NULL is returned, an error message is left
       in the interp's result.

       The result already has its reference count incremented for the  caller.   When  it  is  no
       longer  needed,  that  reference  count should be decremented.  This is needed for thread-
       safety purposes, to allow multiple threads to access this  and  related  functions,  while
       ensuring the results are always valid.

       Tcl_FSChdir replaces the library version of chdir.  The path is normalized and then passed
       to the filesystem which claims it.  If that filesystem does not implement  this  function,
       Tcl  will  fallback  to  a  combination  of stat and access to check whether the directory
       exists and has appropriate permissions.

       For results, see chdir documentation.  If successful, we keep a record of  the  successful
       path in cwdPathPtr for subsequent calls to Tcl_FSGetCwd.

       Tcl_FSPathSeparator  returns  the separator character to be used for most specific element
       of the path specified by pathPtr (i.e. the last part of the path).

       The separator is returned as a Tcl_Obj containing a string of length 1.  If  the  path  is
       invalid, NULL is returned.

       Tcl_FSJoinPath  takes  the  given Tcl_Obj, which must be a valid list (which is allowed to
       have a reference count of zero), and returns the path  object  given  by  considering  the
       first  elements elements as valid path segments (each path segment may be a complete path,
       a partial path or just a single possible directory or file name).  If any path segment  is
       actually  an  absolute  path,  then all prior path segments are discarded.  If elements is
       less than 0, we use the entire list.

       It is possible that the returned object is actually an element of the given list,  so  the
       caller should be careful to increment the reference count of the result before freeing the
       list.

       The returned object, typically with a reference count of zero  (but  it  could  be  shared
       under  some  conditions), contains the joined path.  The caller must add a reference count
       to the object before using it.  In particular, the returned object could be an element  of
       the  given  list,  so  freeing  the list might free the object prematurely if no reference
       count has been taken.  If the number of elements is zero, then the returned object will be
       an empty-string Tcl_Obj.

       Tcl_FSSplitPath  takes  the given Tcl_Obj, which should be a valid path, and returns a Tcl
       list object containing each segment of that path as an element.  It returns a list  object
       with  a  reference  count  of  zero.  If the passed in lenPtr is non-NULL, the variable it
       points to will be updated to contain the number of elements in the returned list.

       Tcl_FSEqualPaths tests whether the two paths given represent the same filesystem object

       It returns 1 if the paths are equal, and 0 if they are different.  If either path is NULL,
       0 is always returned.

       Tcl_FSGetNormalizedPath this important function attempts to extract from the given Tcl_Obj
       a unique normalized path representation, whose string  value  can  be  used  as  a  unique
       identifier for the file.

       It  returns  the  normalized path object, owned by Tcl, or NULL if the path was invalid or
       could otherwise not be successfully converted.  Extraction of absolute,  normalized  paths
       is  very  efficient (because the filesystem operates on these representations internally),
       although the result when the filesystem contains numerous symbolic links may  not  be  the
       most user-friendly version of a path.  The return value is owned by Tcl and has a lifetime
       equivalent to that of the pathPtr passed in (unless that is a relative path, in which case
       the  normalized  path  object  may  be freed any time the cwd changes) - the caller can of
       course increment the refCount if it wishes to maintain a copy for longer.

       Tcl_FSJoinToPath takes the given object, which should usually be a valid path or NULL, and
       joins onto it the array of paths segments given.

       Returns  object,  typically  with  refCount  of  zero  (but  it could be shared under some
       conditions), containing the joined path.  The caller must add a  refCount  to  the  object
       before  using  it.   If  any  of  the  objects  passed into this function (pathPtr or path
       elements) have a refCount of zero, they will be freed when this function returns.

       Tcl_FSConvertToPathType tries to convert the given Tcl_Obj  to  a  valid  Tcl  path  type,
       taking  account  of  the fact that the cwd may have changed even if this object is already
       supposedly of the correct type.  The filename may begin  with  “~”  (to  indicate  current
       user's home directory) or “~<user>” (to indicate any user's home directory).

       If  the  conversion  succeeds  (i.e.  the  object  is  a  valid path in one of the current
       filesystems), then TCL_OK is returned.  Otherwise TCL_ERROR  is  returned,  and  an  error
       message may be left in the interpreter.

       Tcl_FSGetInternalRep  extracts  the internal representation of a given path object, in the
       given filesystem.  If the path object belongs to a different filesystem, we  return  NULL.
       If  the  internal  representation is currently NULL, we attempt to generate it, by calling
       the filesystem's Tcl_FSCreateInternalRepProc.

       Returns NULL or a valid internal path representation.   This  internal  representation  is
       cached, so that repeated calls to this function will not require additional conversions.

       Tcl_FSGetTranslatedPath attempts to extract the translated path from the given Tcl_Obj.

       If  the  translation  succeeds  (i.e.  the  object  is a valid path), then it is returned.
       Otherwise NULL will be returned, and an error message may be left in the  interpreter.   A
       “translated”  path  is  one  which  contains  no “~” or “~user” sequences (these have been
       expanded to their current representation in the filesystem).  The object returned is owned
       by  the  caller,  which  must store it or call Tcl_DecrRefCount to ensure memory is freed.
       This function is of little practical use, and Tcl_FSGetNormalizedPath or Tcl_GetNativePath
       are usually better functions to use for most purposes.

       Tcl_FSGetTranslatedStringPath  does  the  same  as  Tcl_FSGetTranslatedPath, but returns a
       character string or NULL.  The string returned is dynamically allocated and owned  by  the
       caller,   which   must   store   it  or  call  ckfree  to  ensure  it  is  freed.   Again,
       Tcl_FSGetNormalizedPath or Tcl_GetNativePath are usually better functions to use for  most
       purposes.

       Tcl_FSNewNativePath  performs something like the reverse of the usual obj->path->nativerep
       conversions.  If some code retrieves a path in native  form  (from,  e.g.  readlink  or  a
       native  dialog),  and that path is to be used at the Tcl level, then calling this function
       is an efficient way of creating the appropriate path object type.

       The resulting object is a pure “path” object, which  will  only  receive  a  UTF-8  string
       representation if that is required by some Tcl code.

       Tcl_FSGetNativePath is for use by the Win/Unix native filesystems, so that they can easily
       retrieve the native (char* or TCHAR*) representation  of  a  path.   This  function  is  a
       convenience  wrapper around Tcl_FSGetInternalRep, and assumes the native representation is
       string-based.  It  may  be  desirable  in  the  future  to  have  non-string-based  native
       representations  (for  example,  on  MacOSX,  a  representation  using a fileSpec of FSRef
       structure would probably be more efficient).  On Windows  a  full  Unicode  representation
       would  allow  for  paths  of  unlimited  length.  Currently the representation is simply a
       character string which may contain either  the  relative  path  or  a  complete,  absolute
       normalized  path in the native encoding (complex conditions dictate which of these will be
       provided, so neither can be relied upon, unless the path is known to be absolute).  If you
       need a native path which must be absolute, then you should ask for the native version of a
       normalized path.  If for some reason a non-absolute, non-normalized version of the path is
       needed, that must be constructed separately (e.g. using Tcl_FSGetTranslatedPath).

       The  native  representation  is  cached  so  that repeated calls to this function will not
       require additional conversions.  The return value is owned  by  Tcl  and  has  a  lifetime
       equivalent to that of the pathPtr passed in (unless that is a relative path, in which case
       the native representation may be freed any time the cwd changes).

       Tcl_FSFileSystemInfo returns a list of two elements.  The first element is the name of the
       filesystem  (e.g.   “native”,  “vfs”, “zip”, or “prowrap”, perhaps), and the second is the
       particular type of the given path within that filesystem (which is filesystem  dependent).
       The   second  element  may  be  empty  if  the  filesystem  does  not  provide  a  further
       categorization of files.

       A valid list object is returned, unless the path object is not recognized, when NULL  will
       be returned.

       Tcl_FSGetFileSystemForPath  returns the a pointer to the Tcl_Filesystem which accepts this
       path as valid.

       If no filesystem will accept the path, NULL is returned.

       Tcl_FSGetPathType determines whether the given path is relative to the current  directory,
       relative to the current volume, or absolute.

       It returns one of TCL_PATH_ABSOLUTE, TCL_PATH_RELATIVE, or TCL_PATH_VOLUME_RELATIVE

       Tcl_AllocStatBuf  allocates  a Tcl_StatBuf on the system heap (which may be deallocated by
       being passed to ckfree.)  This allows extensions  to  invoke  Tcl_FSStat  and  Tcl_FSLStat
       without being dependent on the size of the buffer.  That in turn depends on the flags used
       to build Tcl.

THE VIRTUAL FILESYSTEM API

       A filesystem provides a Tcl_Filesystem structure that contains pointers to functions  that
       implement  the  various operations on a filesystem; these operations are invoked as needed
       by the generic layer, which generally occurs through the functions listed above.

       The Tcl_Filesystem structures are manipulated using the following methods.

       Tcl_FSRegister takes a pointer to a filesystem structure and an optional piece of data  to
       associated with that filesystem.  On calling this function, Tcl will attach the filesystem
       to the list of known filesystems, and it will become fully  functional  immediately.   Tcl
       does not check if the same filesystem is registered multiple times (and in general that is
       not a good thing to do).  TCL_OK will be returned.

       Tcl_FSUnregister  removes  the  given  filesystem  structure  from  the  list   of   known
       filesystems,  if  it  is  known,  and  returns TCL_OK.  If the filesystem is not currently
       registered, TCL_ERROR is returned.

       Tcl_FSData will return the ClientData  associated  with  the  given  filesystem,  if  that
       filesystem is registered.  Otherwise it will return NULL.

       Tcl_FSMountsChanged  is used to inform the Tcl's core that the set of mount points for the
       given (already registered) filesystem have changed, and that cached  file  representations
       may therefore no longer be correct.

   THE TCL_FILESYSTEM STRUCTURE
       The Tcl_Filesystem structure contains the following fields:
              typedef struct Tcl_Filesystem {
                  const char *typeName;
                  int structureLength;
                  Tcl_FSVersion version;
                  Tcl_FSPathInFilesystemProc *pathInFilesystemProc;
                  Tcl_FSDupInternalRepProc *dupInternalRepProc;
                  Tcl_FSFreeInternalRepProc *freeInternalRepProc;
                  Tcl_FSInternalToNormalizedProc *internalToNormalizedProc;
                  Tcl_FSCreateInternalRepProc *createInternalRepProc;
                  Tcl_FSNormalizePathProc *normalizePathProc;
                  Tcl_FSFilesystemPathTypeProc *filesystemPathTypeProc;
                  Tcl_FSFilesystemSeparatorProc *filesystemSeparatorProc;
                  Tcl_FSStatProc *statProc;
                  Tcl_FSAccessProc *accessProc;
                  Tcl_FSOpenFileChannelProc *openFileChannelProc;
                  Tcl_FSMatchInDirectoryProc *matchInDirectoryProc;
                  Tcl_FSUtimeProc *utimeProc;
                  Tcl_FSLinkProc *linkProc;
                  Tcl_FSListVolumesProc *listVolumesProc;
                  Tcl_FSFileAttrStringsProc *fileAttrStringsProc;
                  Tcl_FSFileAttrsGetProc *fileAttrsGetProc;
                  Tcl_FSFileAttrsSetProc *fileAttrsSetProc;
                  Tcl_FSCreateDirectoryProc *createDirectoryProc;
                  Tcl_FSRemoveDirectoryProc *removeDirectoryProc;
                  Tcl_FSDeleteFileProc *deleteFileProc;
                  Tcl_FSCopyFileProc *copyFileProc;
                  Tcl_FSRenameFileProc *renameFileProc;
                  Tcl_FSCopyDirectoryProc *copyDirectoryProc;
                  Tcl_FSLstatProc *lstatProc;
                  Tcl_FSLoadFileProc *loadFileProc;
                  Tcl_FSGetCwdProc *getCwdProc;
                  Tcl_FSChdirProc *chdirProc;
              } Tcl_Filesystem;

       Except  for  the  first three fields in this structure which contain simple data elements,
       all entries contain addresses of functions called  by  the  generic  filesystem  layer  to
       perform the complete range of filesystem related actions.

       The many functions in this structure are broken down into three categories: infrastructure
       functions (almost all of which must be implemented), operational functions (which must  be
       implemented  if  a  complete filesystem is provided), and efficiency functions (which need
       only be implemented if they can be done so efficiently, or if they have side-effects which
       are  required  by  the filesystem; Tcl has less efficient emulations it can fall back on).
       It is important to note that, in the current version of Tcl, most of these  fallbacks  are
       only  used  to  handle  commands initiated in Tcl, not in C. What this means is, that if a
       file rename command is issued in Tcl, and the  relevant  filesystem(s)  do  not  implement
       their  Tcl_FSRenameFileProc,  Tcl's  core  will instead fallback on a combination of other
       filesystem functions (it will use Tcl_FSCopyFileProc followed by Tcl_FSDeleteFileProc, and
       if  Tcl_FSCopyFileProc  is  not  implemented  there is a further fallback).  However, if a
       Tcl_FSRenameFileProc command is issued at the C level, no such fallbacks occur.   This  is
       true  except  for  the  last four entries in the filesystem table (lstat, load, getcwd and
       chdir) for which fallbacks do in fact occur at the C level.

       Any functions which take path names in Tcl_Obj form take those names in UTF-8  form.   The
       filesystem infrastructure API is designed to support efficient, cached conversion of these
       UTF-8 paths to other native representations.

   EXAMPLE FILESYSTEM DEFINITION
       Here is the filesystem lookup table used by the “vfs” extension  which  allows  filesystem
       actions to be implemented in Tcl.
              static Tcl_Filesystem vfsFilesystem = {
                  "tclvfs",
                  sizeof(Tcl_Filesystem),
                  TCL_FILESYSTEM_VERSION_1,
                  &VfsPathInFilesystem,
                  &VfsDupInternalRep,
                  &VfsFreeInternalRep,
                  /* No internal to normalized, since we don't create
                   * any pure 'internal' Tcl_Obj path representations */
                  NULL,
                  /* No create native rep function, since we don't use
                   * it and don't choose to support uses of
                   * Tcl_FSNewNativePath */
                  NULL,
                  /* Normalize path isn't needed - we assume paths only
                   * have one representation */
                  NULL,
                  &VfsFilesystemPathType,
                  &VfsFilesystemSeparator,
                  &VfsStat,
                  &VfsAccess,
                  &VfsOpenFileChannel,
                  &VfsMatchInDirectory,
                  &VfsUtime,
                  /* We choose not to support symbolic links inside our
                   * VFS's */
                  NULL,
                  &VfsListVolumes,
                  &VfsFileAttrStrings,
                  &VfsFileAttrsGet,
                  &VfsFileAttrsSet,
                  &VfsCreateDirectory,
                  &VfsRemoveDirectory,
                  &VfsDeleteFile,
                  /* No copy file; use the core fallback mechanism */
                  NULL,
                  /* No rename file; use the core fallback mechanism */
                  NULL,
                  /* No copy directory; use the core fallback mechanism */
                  NULL,
                  /* Core will use stat for lstat */
                  NULL,
                  /* No load; use the core fallback mechanism */
                  NULL,
                  /* We don't need a getcwd or chdir; the core's own
                   * internal value is suitable */
                  NULL,
                  NULL
              };

FILESYSTEM INFRASTRUCTURE

       These  fields  contain  basic  information about the filesystem structure and addresses of
       functions which are used to associate a particular filesystem with a file path,  and  deal
       with  the  internal handling of path representations, for example copying and freeing such
       representations.

   TYPENAME
       The typeName field contains a null-terminated string  that  identifies  the  type  of  the
       filesystem implemented, e.g.  “native”, “zip” or “vfs”.

   STRUCTURE LENGTH
       The structureLength field is generally implemented as sizeof(Tcl_Filesystem), and is there
       to allow easier binary backwards compatibility if the size of the structure changes  in  a
       future Tcl release.

   VERSION
       The version field should be set to TCL_FILESYSTEM_VERSION_1.

   PATHINFILESYSTEMPROC
       The  pathInFilesystemProc  field  contains  the  address  of a function which is called to
       determine whether a given path object belongs to this filesystem or not.   Tcl  will  only
       call the rest of the filesystem functions with a path for which this function has returned
       TCL_OK.  If the path does not belong, -1 should be returned (the behaviour of Tcl for  any
       other   return  value  is  not  defined).   If  TCL_OK  is  returned,  then  the  optional
       clientDataPtr output parameter can be used to return  an  internal  (filesystem  specific)
       representation  of  the  path,  which  will  be  cached inside the path object, and may be
       retrieved efficiently by the other filesystem functions.  Tcl  will  simultaneously  cache
       the  fact  that  this  path  belongs to this filesystem.  Such caches are invalidated when
       filesystem structures are added or removed from Tcl's internal list of known filesystems.

              typedef int Tcl_FSPathInFilesystemProc(
                      Tcl_Obj *pathPtr,
                      ClientData *clientDataPtr);

   DUPINTERNALREPPROC
       This function makes a copy of a path's internal representation, and  is  called  when  Tcl
       needs  to  duplicate  a  path  object.   If  NULL,  Tcl  will simply not copy the internal
       representation, which may then need to be regenerated later.

              typedef ClientData Tcl_FSDupInternalRepProc(
                      ClientData clientData);

   FREEINTERNALREPPROC
       Free the internal representation.  This must be implemented  if  internal  representations
       need  freeing  (i.e.  if  some  memory  is  allocated  when  an internal representation is
       generated), but may otherwise be NULL.

              typedef void Tcl_FSFreeInternalRepProc(
                      ClientData clientData);

   INTERNALTONORMALIZEDPROC
       Function to convert internal representation to a normalized path.  Only  required  if  the
       filesystem creates pure path objects with no string/path representation.  The return value
       is a Tcl object whose string representation is the normalized path.

              typedef Tcl_Obj* Tcl_FSInternalToNormalizedProc(
                      ClientData clientData);

   CREATEINTERNALREPPROC
       Function to take a path object, and calculate an internal representation for it, and store
       that  native  representation  in  the  object.   May  be  NULL  if  paths have no internal
       representation,  or  if  the  Tcl_FSPathInFilesystemProc  for   this   filesystem   always
       immediately creates an internal representation for paths it accepts.

              typedef ClientData Tcl_FSCreateInternalRepProc(
                      Tcl_Obj *pathPtr);

   NORMALIZEPATHPROC
       Function  to  normalize  a path.  Should be implemented for all filesystems which can have
       multiple string representations for the same path object.  In Tcl, every “path” must  have
       a  single  unique  “normalized” string representation.  Depending on the filesystem, there
       may be more than one unnormalized string representation which refers to that path (e.g.  a
       relative path, a path with different character case if the filesystem is case insensitive,
       a path contain a reference to a home directory such as “~”,  a  path  containing  symbolic
       links,  etc).  If the very last component in the path is a symbolic link, it should not be
       converted into the object it points to (but its case  or  other  aspects  should  be  made
       unique).   All  other  path  components should be converted from symbolic links.  This one
       exception is required to agree with Tcl's semantics with file delete,  file  rename,  file
       copy  operating on symbolic links.  This function may be called with nextCheckpoint either
       at the beginning of the path (i.e. zero), at the end of the path, or at  any  intermediate
       file  separator  in  the path.  It will never point to any other arbitrary position in the
       path. In the last of the three valid cases, the implementation can assume that the path up
       to and including the file separator is known and normalized.

              typedef int Tcl_FSNormalizePathProc(
                      Tcl_Interp *interp,
                      Tcl_Obj *pathPtr,
                      int nextCheckpoint);

FILESYSTEM OPERATIONS

       The  fields  in  this  section  of  the structure contain addresses of functions which are
       called to carry out the basic filesystem operations.  A filesystem  which  expects  to  be
       used  with  the complete standard Tcl command set must implement all of these.  If some of
       them are not implemented, then certain Tcl commands  may  fail  when  operating  on  paths
       within  that filesystem.  However, in some instances this may be desirable (for example, a
       read-only filesystem should not implement the last four functions, and a filesystem  which
       does  not  support  symbolic links need not implement the readlink function, etc.  The Tcl
       core expects filesystems to behave in this way).

   FILESYSTEMPATHTYPEPROC
       Function to determine the type of a path in this filesystem.  May be NULL, in  which  case
       no type information will be available to users of the filesystem.  The “type” is used only
       for informational purposes, and should be returned as the  string  representation  of  the
       Tcl_Obj  which  is returned.  A typical return value might be “networked”, “zip” or “ftp”.
       The Tcl_Obj result is owned by the filesystem and so Tcl will increment  the  refCount  of
       that object if it wishes to retain a reference to it.

              typedef Tcl_Obj* Tcl_FSFilesystemPathTypeProc(
                      Tcl_Obj *pathPtr);

   FILESYSTEMSEPARATORPROC
       Function  to  return  the  separator  character(s) for this filesystem.  This need only be
       implemented if the filesystem wishes to use a different separator than the standard string
       “/”.   Amongst other uses, it is returned by the file separator command.  The return value
       should be an object with refCount of zero.

              typedef Tcl_Obj* Tcl_FSFilesystemSeparatorProc(
                      Tcl_Obj *pathPtr);

   STATPROC
       Function to process a Tcl_FSStat call.  Must be implemented for any reasonable filesystem,
       since many Tcl level commands depend crucially upon it (e.g. file atime, file isdirectory,
       file size, glob).

              typedef int Tcl_FSStatProc(
                      Tcl_Obj *pathPtr,
                      Tcl_StatBuf *statPtr);

       The Tcl_FSStatProc fills the stat structure statPtr with information about  the  specified
       file.   You do not need any access rights to the file to get this information but you need
       search rights to all directories named  in  the  path  leading  to  the  file.   The  stat
       structure  includes  info  regarding  device, inode (always 0 on Windows), privilege mode,
       nlink (always 1 on Windows), user id  (always  0  on  Windows),  group  id  (always  0  on
       Windows),  rdev  (same  as  device  on Windows), size, last access time, last modification
       time, and last metadata change time.

       If the file represented by pathPtr exists, the  Tcl_FSStatProc  returns  0  and  the  stat
       structure is filled with data.  Otherwise, -1 is returned, and no stat info is given.

   ACCESSPROC
       Function  to  process  a  Tcl_FSAccess  call.   Must  be  implemented  for  any reasonable
       filesystem, since many Tcl level commands depend crucially upon it (e.g. file exists, file
       readable).

              typedef int Tcl_FSAccessProc(
                      Tcl_Obj *pathPtr,
                      int mode);

       The  Tcl_FSAccessProc  checks  whether the process would be allowed to read, write or test
       for existence of the file (or other filesystem object) whose name is in pathPtr.   If  the
       pathname  refers  to  a  symbolic  link, then the permissions of the file referred by this
       symbolic link should be tested.

       On success (all requested permissions granted), zero is returned.  On error (at least  one
       bit  in  mode asked for a permission that is denied, or some other  error occurred), -1 is
       returned.

   OPENFILECHANNELPROC
       Function to process a Tcl_FSOpenFileChannel call.  Must be implemented for any  reasonable
       filesystem,  since  any  operations which require open or accessing a file's contents will
       use it (e.g. open, encoding, and many Tk commands).

              typedef Tcl_Channel Tcl_FSOpenFileChannelProc(
                      Tcl_Interp *interp,
                      Tcl_Obj *pathPtr,
                      int mode,
                      int permissions);

       The Tcl_FSOpenFileChannelProc opens a file specified by  pathPtr  and  returns  a  channel
       handle  that  can  be  used  to perform input and output on the file.  This API is modeled
       after the fopen procedure of the Unix standard I/O library.  The syntax and meaning of all
       arguments is similar to those given in the Tcl open command when opening a file, where the
       mode argument is a combination of the POSIX flags O_RDONLY, O_WRONLY, etc.   If  an  error
       occurs while opening the channel, the Tcl_FSOpenFileChannelProc returns NULL and records a
       POSIX error code that can be retrieved with Tcl_GetErrno.  In addition, if interp is  non-
       NULL,  the  Tcl_FSOpenFileChannelProc leaves an error message in interp's result after any
       error.

       The newly created channel must not registered in the supplied interpreter; that task is up
       to  the  caller  of Tcl_FSOpenFileChannel (if necessary). If one of the standard channels,
       stdin, stdout or stderr was previously closed, the act of creating the  new  channel  also
       assigns it as a replacement for the standard channel.

   MATCHINDIRECTORYPROC
       Function  to  process  a  Tcl_FSMatchInDirectory  call.  If not implemented, then glob and
       recursive copy functionality will be lacking  in  the  filesystem  (and  this  may  impact
       commands like encoding names which use glob functionality internally).

              typedef int Tcl_FSMatchInDirectoryProc(
                      Tcl_Interp* interp,
                      Tcl_Obj *resultPtr,
                      Tcl_Obj *pathPtr,
                      const char *pattern,
                      Tcl_GlobTypeData *types);

       The  function  should  return all files or directories (or other filesystem objects) which
       match the given pattern and accord with the types specification given.  There are two ways
       in  which  this  function  may be called.  If pattern is NULL, then pathPtr is a full path
       specification of a single file or directory which should  be  checked  for  existence  and
       correct  type.   Otherwise,  pathPtr  is  a  directory, the contents of which the function
       should search for files or directories which have  the  correct  type.   In  either  case,
       pathPtr  can be assumed to be both non-NULL and non-empty.  It is not currently documented
       whether pathPtr will have a file separator at its end of not, so code should  be  flexible
       to both possibilities.

       The  return  value  is  a  standard Tcl result indicating whether an error occurred in the
       matching process.  Error messages are placed in interp, unless interp  in  NULL  in  which
       case  no  error  message need be generated; on a TCL_OK result, results should be added to
       the resultPtr object given (which can be assumed to be a valid unshared  Tcl  list).   The
       matches  added  to resultPtr should include any path prefix given in pathPtr (this usually
       means they will be absolute path specifications).  Note that if no matches are found, that
       simply  leads  to  an empty result; errors are only signaled for actual file or filesystem
       problems which may occur during the matching process.

       The Tcl_GlobTypeData structure passed  in  the  types  parameter  contains  the  following
       fields:
              typedef struct Tcl_GlobTypeData {
                      /* Corresponds to bcdpfls as in 'find -t' */
                      int type;
                      /* Corresponds to file permissions */
                      int perm;
                      /* Acceptable mac type */
                      Tcl_Obj *macType;
                      /* Acceptable mac creator */
                      Tcl_Obj *macCreator;
              } Tcl_GlobTypeData;

       There are two specific cases which it is important to handle correctly, both when types is
       non-NULL. The two cases are  when  types->types  &  TCL_GLOB_TYPE_DIR  or  types->types  &
       TCL_GLOB_TYPE_MOUNT  are  true (and in particular when the other flags are false).  In the
       first of these cases, the function must list the contained directories.  Tcl uses this  to
       implement  recursive  globbing,  so  it  is  critical that filesystems implement directory
       matching  correctly.   In  the  second  of  these  cases,  with  TCL_GLOB_TYPE_MOUNT,  the
       filesystem  must  list  the  mount  points which lie within the given pathPtr (and in this
       case, pathPtr need not lie within the same filesystem - different to all  other  cases  in
       which  this  function is called).  Support for this is critical if Tcl is to have seamless
       transitions between from one filesystem to another.

   UTIMEPROC
       Function to process a Tcl_FSUtime call.  Required to allow setting (not reading) of  times
       with file mtime, file atime and the open-r/open-w/fcopy implementation of file copy.

              typedef int Tcl_FSUtimeProc(
                      Tcl_Obj *pathPtr,
                      struct utimbuf *tval);

       The  access  and  modification times of the file specified by pathPtr should be changed to
       the values given in the tval structure.

       The return value should be 0 on success and -1 on an error, as with the system utime.

   LINKPROC
       Function to process a Tcl_FSLink call.  Should  be  implemented  only  if  the  filesystem
       supports links, and may otherwise be NULL.

              typedef Tcl_Obj* Tcl_FSLinkProc(
                      Tcl_Obj *linkNamePtr,
                      Tcl_Obj *toPtr,
                      int linkAction);

       If  toPtr is NULL, the function is being asked to read the contents of a link.  The result
       is a Tcl_Obj specifying the contents of the link given by linkNamePtr, or NULL if the link
       could  not  be read.  The result is owned by the caller (and should therefore have its ref
       count incremented before being returned).  Any callers  should  call  Tcl_DecrRefCount  on
       this  result  when  it  is  no  longer  needed.  If toPtr is not NULL, the function should
       attempt to create a link.  The result in this  case  should  be  toPtr  if  the  link  was
       successful  and  NULL otherwise.  In this case the result is not owned by the caller (i.e.
       no ref count manipulation on either end is needed). See the documentation  for  Tcl_FSLink
       for the correct interpretation of the linkAction flags.

   LISTVOLUMESPROC
       Function  to  list any filesystem volumes added by this filesystem.  Should be implemented
       only if the filesystem adds volumes at the head of the filesystem, so  that  they  can  be
       returned by file volumes.

              typedef Tcl_Obj* Tcl_FSListVolumesProc(void);

       The  result  should  be  a  list of volumes added by this filesystem, or NULL (or an empty
       list) if no volumes are provided.  The result object is considered  to  be  owned  by  the
       filesystem  (not by Tcl's core), but should be given a refCount for Tcl.  Tcl will use the
       contents of the list and then decrement that refCount.  This allows filesystems to  choose
       whether  they  actually  want  to  retain  a “master list” of volumes or not (if not, they
       generate the list on the fly and pass it to Tcl with a refCount of 1 and then forget about
       the list, if yes, then they simply increment the refCount of their master list and pass it
       to Tcl which will copy the contents and then decrement the count back to where it was).

       Therefore, Tcl considers return values from this proc to be read-only.

   FILEATTRSTRINGSPROC
       Function to list all attribute strings which  are  valid  for  this  filesystem.   If  not
       implemented  the  filesystem  will  not  support the file attributes command.  This allows
       arbitrary additional information to be attached to files in the filesystem.  If it is  not
       implemented, there is no need to implement the get and set methods.

              typedef const char** Tcl_FSFileAttrStringsProc(
                      Tcl_Obj *pathPtr,
                      Tcl_Obj** objPtrRef);

       The  called function may either return an array of strings, or may instead return NULL and
       place a Tcl list into the given objPtrRef.  Tcl will take that list  and  first  increment
       its  reference  count  before using it.  On completion of that use, Tcl will decrement its
       reference count.  Hence if the list should be disposed of by Tcl when done, it should have
       a  reference  count  of  zero,  and  if the list should not be disposed of, the filesystem
       should ensure it returns an object with a reference count of at least one.

   FILEATTRSGETPROC
       Function to process a Tcl_FSFileAttrsGet call, used by file attributes.

              typedef int Tcl_FSFileAttrsGetProc(
                      Tcl_Interp *interp,
                      int index,
                      Tcl_Obj *pathPtr,
                      Tcl_Obj **objPtrRef);

       Returns a standard Tcl return code.  The attribute value retrieved, which  corresponds  to
       the  index'th  element in the list returned by the Tcl_FSFileAttrStringsProc, is a Tcl_Obj
       placed in objPtrRef (if TCL_OK was returned) and is likely to have a  reference  count  of
       zero.   Either  way  we must either store it somewhere (e.g. the Tcl result), or Incr/Decr
       its reference count to ensure it is properly freed.

   FILEATTRSSETPROC
       Function to process a Tcl_FSFileAttrsSet call, used by file attributes.  If the filesystem
       is read-only, there is no need to implement this.

              typedef int Tcl_FSFileAttrsSetProc(
                      Tcl_Interp *interp,
                      int index,
                      Tcl_Obj *pathPtr,
                      Tcl_Obj *objPtr);

       The   attribute   value   of   the   index'th   element   in  the  list  returned  by  the
       Tcl_FSFileAttrStringsProc should be set to the objPtr given.

   CREATEDIRECTORYPROC
       Function to process a Tcl_FSCreateDirectory call.  Should be implemented unless the FS  is
       read-only.

              typedef int Tcl_FSCreateDirectoryProc(
                      Tcl_Obj *pathPtr);

       The  return  value  is  a  standard Tcl result indicating whether an error occurred in the
       process.  If successful, a new directory should have been added to the filesystem  in  the
       location specified by pathPtr.

   REMOVEDIRECTORYPROC
       Function  to process a Tcl_FSRemoveDirectory call.  Should be implemented unless the FS is
       read-only.

              typedef int Tcl_FSRemoveDirectoryProc(
                      Tcl_Obj *pathPtr,
                      int recursive,
                      Tcl_Obj **errorPtr);

       The return value is a standard Tcl result indicating whether  an  error  occurred  in  the
       process.   If successful, the directory specified by pathPtr should have been removed from
       the filesystem.  If the recursive flag is given, then  a  non-empty  directory  should  be
       deleted  without  error.  If this flag is not given, then and the directory is non-empty a
       POSIX “EEXIST” error should be signaled.  If an error does occur, the name of the file  or
       directory which caused the error should be placed in errorPtr.

   DELETEFILEPROC
       Function to process a Tcl_FSDeleteFile call.  Should be implemented unless the FS is read-
       only.

              typedef int Tcl_FSDeleteFileProc(
                      Tcl_Obj *pathPtr);

       The return value is a standard Tcl result indicating whether  an  error  occurred  in  the
       process.   If  successful, the file specified by pathPtr should have been removed from the
       filesystem.  Note that, if the filesystem supports symbolic links, Tcl  will  always  call
       this  function  and not Tcl_FSRemoveDirectoryProc when needed to delete them (even if they
       are symbolic links to directories).

FILESYSTEM EFFICIENCY

       These functions need not be implemented for a particular filesystem because the core has a
       fallback implementation available. See each individual description for the consequences of
       leaving the field NULL.

   LSTATPROC
       Function to process a Tcl_FSLstat call.  If not implemented, Tcl will attempt to  use  the
       statProc defined above instead.  Therefore it need only be implemented if a filesystem can
       differentiate between stat and lstat calls.

              typedef int Tcl_FSLstatProc(
                      Tcl_Obj *pathPtr,
                      Tcl_StatBuf *statPtr);

       The behavior of this function is very similar to that of the Tcl_FSStatProc defined above,
       except  that  if  it is applied to a symbolic link, it returns information about the link,
       not about the target file.

   COPYFILEPROC
       Function to process a Tcl_FSCopyFile call.  If not implemented Tcl will fall back on open-
       r,  open-w and fcopy as a copying mechanism.  Therefore it need only be implemented if the
       filesystem can perform that action more efficiently.

              typedef int Tcl_FSCopyFileProc(
                      Tcl_Obj *srcPathPtr,
                      Tcl_Obj *destPathPtr);

       The return value is a standard Tcl result indicating whether  an  error  occurred  in  the
       copying  process.   Note that, destPathPtr is the name of the file which should become the
       copy of srcPathPtr. It is never the name of a directory into  which  srcPathPtr  could  be
       copied  (i.e. the function is much simpler than the Tcl level file copy subcommand).  Note
       that, if the filesystem supports symbolic links, Tcl will always call  this  function  and
       not  copyDirectoryProc  when  needed  to  copy  them  (even  if they are symbolic links to
       directories).  Finally, if the filesystem determines  it  cannot  support  the  file  copy
       action, calling Tcl_SetErrno(EXDEV) and returning a non-TCL_OK result will tell Tcl to use
       its standard fallback mechanisms.

   RENAMEFILEPROC
       Function to process a Tcl_FSRenameFile call.  If not implemented, Tcl will fall back on  a
       copy  and  delete  mechanism.  Therefore it need only be implemented if the filesystem can
       perform that action more efficiently.

              typedef int Tcl_FSRenameFileProc(
                      Tcl_Obj *srcPathPtr,
                      Tcl_Obj *destPathPtr);

       The return value is a standard Tcl result indicating whether  an  error  occurred  in  the
       renaming  process.  If the filesystem determines it cannot support the file rename action,
       calling Tcl_SetErrno(EXDEV) and returning a non-TCL_OK result will tell  Tcl  to  use  its
       standard fallback mechanisms.

   COPYDIRECTORYPROC
       Function to process a Tcl_FSCopyDirectory call.  If not implemented, Tcl will fall back on
       a recursive file mkdir, file copy mechanism.  Therefore it need only be implemented if the
       filesystem can perform that action more efficiently.

              typedef int Tcl_FSCopyDirectoryProc(
                      Tcl_Obj *srcPathPtr,
                      Tcl_Obj *destPathPtr,
                      Tcl_Obj **errorPtr);

       The  return  value  is  a  standard Tcl result indicating whether an error occurred in the
       copying process.  If an error does occur, the name of the file or directory  which  caused
       the  error  should  be  placed  in  errorPtr.  Note  that,  destPathPtr is the name of the
       directory-name which should become the mirror-image of srcPathPtr. It is not the name of a
       directory  into  which srcPathPtr should be copied (i.e. the function is much simpler than
       the Tcl level file copy subcommand).  Finally, if  the  filesystem  determines  it  cannot
       support  the directory copy action, calling Tcl_SetErrno(EXDEV) and returning a non-TCL_OK
       result will tell Tcl to use its standard fallback mechanisms.

   LOADFILEPROC
       Function to process a Tcl_FSLoadFile call.  If not implemented, Tcl will fall  back  on  a
       copy  to  native-temp  followed  by a Tcl_FSLoadFile on that temporary copy.  Therefore it
       need only be implemented  if  the  filesystem  can  load  code  directly,  or  it  can  be
       implemented  simply  to  return TCL_ERROR to disable load functionality in this filesystem
       entirely.

              typedef int Tcl_FSLoadFileProc(
                      Tcl_Interp *interp,
                      Tcl_Obj *pathPtr,
                      Tcl_LoadHandle *handlePtr,
                      Tcl_FSUnloadFileProc *unloadProcPtr);

       Returns a standard Tcl completion code.  If an error occurs, an error message is  left  in
       the interp's result.  The function dynamically loads a binary code file into memory.  On a
       successful load, the handlePtr should be filled with a token for  the  dynamically  loaded
       file,  and  the  unloadProcPtr  should  be filled in with the address of a procedure.  The
       unload procedure will be called with the given Tcl_LoadHandle as its only  parameter  when
       Tcl  needs to unload the file.  For example, for the native filesystem, the Tcl_LoadHandle
       returned is currently a token which can be used in the private  TclpFindSymbol  to  access
       functions  in  the  new  code.  Each filesystem is free to define the Tcl_LoadHandle as it
       requires.  Finally, if the filesystem determines it cannot support the file  load  action,
       calling  Tcl_SetErrno(EXDEV)  and  returning  a non-TCL_OK result will tell Tcl to use its
       standard fallback mechanisms.

   UNLOADFILEPROC
       Function to unload a previously successfully loaded file.  If load was  implemented,  then
       this should also be implemented, if there is any cleanup action required.

              typedef void Tcl_FSUnloadFileProc(
                      Tcl_LoadHandle loadHandle);

   GETCWDPROC
       Function  to  process  a Tcl_FSGetCwd call.  Most filesystems need not implement this.  It
       will usually only be called once, if getcwd is called before chdir.  May be NULL.

              typedef Tcl_Obj* Tcl_FSGetCwdProc(
                      Tcl_Interp *interp);

       If the filesystem supports a native notion of a current  working  directory  (which  might
       perhaps change independent of Tcl), this function should return that cwd as the result, or
       NULL if the current directory could not  be  determined  (e.g.  the  user  does  not  have
       appropriate  permissions  on the cwd directory).  If NULL is returned, an error message is
       left in the interp's result.

   CHDIRPROC
       Function to process a Tcl_FSChdir call.  If filesystems do not implement this, it will  be
       emulated  by a series of directory access checks.  Otherwise, virtual filesystems which do
       implement it need only respond with a positive return result if the pathPtr  is  a  valid,
       accessible  directory  in their filesystem.  They need not remember the result, since that
       will be automatically remembered for use by Tcl_FSGetCwd.  Real filesystems  should  carry
       out the correct action (i.e. call the correct system chdir API).

              typedef int Tcl_FSChdirProc(
                      Tcl_Obj *pathPtr);

       The  Tcl_FSChdirProc  changes  the  applications  current  working  directory to the value
       specified in pathPtr. The function returns -1 on error or 0 on success.

SEE ALSO

       cd(3tcl), file(3tcl), load(3tcl), open(3tcl), pwd(3tcl), unload(3tcl)

KEYWORDS

       stat, access, filesystem, vfs, virtual