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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>
     #include <sys/uio.h>

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

     int
     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);

     int
     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);

     int
     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() 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(), and extattr_delete_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() and extattr_set_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() returns 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(), and extattr_delete_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.