NAME

     extattr_get_fd, extattr_set_fd, extattr_delete_fd, extattr_list_fd, extattr_get_file,
     extattr_set_file, extattr_delete_file, extattr_list_file, extattr_get_link,
     extattr_set_link, extattr_delete_link, extattr_list_link — system calls to manipulate VFS
     extended attributes

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/types.h>
     #include <sys/extattr.h>

     ssize_t
     extattr_get_fd(int fd, int attrnamespace, const char *attrname, void *data, size_t nbytes);

     ssize_t
     extattr_set_fd(int fd, int attrnamespace, const char *attrname, const void *data,
         size_t nbytes);

     int
     extattr_delete_fd(int fd, int attrnamespace, const char *attrname);

     ssize_t
     extattr_list_fd(int fd, int attrnamespace, void *data, size_t nbytes);

     ssize_t
     extattr_get_file(const char *path, int attrnamespace, const char *attrname, void *data,
         size_t nbytes);

     ssize_t
     extattr_set_file(const char *path, int attrnamespace, const char *attrname,
         const void *data, size_t nbytes);

     int
     extattr_delete_file(const char *path, int attrnamespace, const char *attrname);

     ssize_t
     extattr_list_file(const char *path, int attrnamespace, void *data, size_t nbytes);

     ssize_t
     extattr_get_link(const char *path, int attrnamespace, const char *attrname, void *data,
         size_t nbytes);

     ssize_t
     extattr_set_link(const char *path, int attrnamespace, const char *attrname,
         const void *data, size_t nbytes);

     int
     extattr_delete_link(const char *path, int attrnamespace, const char *attrname);

     ssize_t
     extattr_list_link(const char *path, int attrnamespace, void *data, size_t nbytes);

DESCRIPTION

     Named extended attributes are meta-data associated with vnodes representing files and
     directories.  They exist as "name=value" pairs within a set of namespaces.

     The extattr_get_file() system call retrieves the value of the specified extended attribute
     into a buffer pointed to by data of size nbytes.  The extattr_set_file() system call sets
     the value of the specified extended attribute to the data described by data.  The
     extattr_delete_file() system call deletes the extended attribute specified.  The
     extattr_list_file() returns a list of attributes present in the requested namespace.  Each
     list entry consists of a single byte containing the length of the attribute name, followed
     by the attribute name.  The attribute name is not terminated by ASCII 0 (nul).  The
     extattr_get_file(), and extattr_list_file() calls consume the data and nbytes arguments in
     the style of read(2); extattr_set_file() consumes these arguments in the style of write(2).

     If data is NULL in a call to extattr_get_file() and extattr_list_file() then the size of
     defined extended attribute data will be returned, rather than the quantity read, permitting
     applications to test the size of the data without performing a read.  The
     extattr_delete_link(), extattr_get_link(), and extattr_set_link() system calls behave in the
     same way as their _file counterparts, except that they do not follow symlinks.

     The extattr_get_fd(), extattr_set_fd(), extattr_delete_fd(), and extattr_list_fd(), calls
     are identical to their "_file" counterparts except for the first argument.  The "_fd"
     functions take a file descriptor, while the "_file" functions take a path.  Both arguments
     describe a file associated with the extended attribute that should be manipulated.

     The following arguments are common to all the system calls described here:

     attrnamespace  the namespace in which the extended attribute resides; see extattr(9)

     attrname       the name of the extended attribute

     Named extended attribute semantics vary by file system implementing the call.  Not all
     operations may be supported for a particular attribute.  Additionally, the format of the
     data in data is attribute-specific.

     For more information on named extended attributes, please see extattr(9).

CAVEAT

     This interface is under active development, and as such is subject to change as applications
     are adapted to use it.  Developers are discouraged from relying on its stability.

RETURN VALUES

     If successful, the extattr_get_file(), extattr_set_file(), and extattr_list_file() calls
     return the number of bytes that were read or written from the data, respectively, or if data
     was NULL, then extattr_get_file() and extattr_list_file() return the number of bytes
     available to read.  If any of the calls are unsuccessful, the value -1 is returned and the
     global variable errno is set to indicate the error.

     The extattr_delete_file() function returns the value 0 if successful; otherwise the value -1
     is returned and the global variable errno is set to indicate the error.

ERRORS

     The following errors may be returned by the system calls themselves.  Additionally, the file
     system implementing the call may return any other errors it desires.

     [EFAULT]           The attrnamespace and attrname arguments, or the memory range defined by
                        data and nbytes point outside the process's allocated address space.

     [ENAMETOOLONG]     The attribute name was longer than EXTATTR_MAXNAMELEN.

     The extattr_get_fd(), extattr_set_fd(), extattr_delete_fd(), and extattr_list_fd() system
     calls may also fail if:

     [EBADF]            The file descriptor referenced by fd was invalid.

     Additionally, the extattr_get_file(), extattr_set_file(), and extattr_delete_file() calls
     may also fail due to the following errors:

     [ENOATTR]          The requested attribute was not defined for this file.

     [ENOTDIR]          A component of the path prefix is not a directory.

     [ENAMETOOLONG]     A component of a pathname exceeded 255 characters, or an entire path name
                        exceeded 1023 characters.

     [ENOENT]           A component of the path name that must exist does not exist.

     [EACCES]           Search permission is denied for a component of the path prefix.

SEE ALSO

     extattr(3), getextattr(8), setextattr(8), extattr(9), VOP_GETEXTATTR(9), VOP_SETEXTATTR(9)

HISTORY

     Extended attribute support was developed as part of the TrustedBSD Project, and introduced
     in FreeBSD 5.0.  It was developed to support security extensions requiring additional labels
     to be associated with each file or directory.

BUGS

     In earlier versions of this API, passing an empty string for the attribute name to
     extattr_get_fd(), extattr_get_file(), or extattr_get_link() would return the list of
     attributes defined for the target object.  This interface has been deprecated in preference
     to using the explicit list API, and should not be used.