free_handle man page on aLinux

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HANDLE(3)							     HANDLE(3)

NAME
       path_to_handle,	 path_to_fshandle,  fd_to_handle,  handle_to_fshandle,
       open_by_handle,	      readlink_by_handle,	 attr_multi_by_handle,
       attr_list_by_handle, fssetdm_by_handle, free_handle, getparents_by_han‐
       dle, getparentpaths_by_handle - file handle operations

C SYNOPSIS
       #include <sys/types.h>
       #include <xfs/handle.h>

       int path_to_handle(char *path, void **hanp, size_t *hlen);

       int path_to_fshandle(char *path, void **hanp, size_t *hlen);

       int fd_to_handle(int fd, void **hanp, size_t *hlen);

       int handle_to_fshandle(void *hanp, size_t hlen, void  **fshanp,	size_t
	      *fshlen);

       int open_by_handle(void *hanp, size_t hlen, int oflag);

       int readlink_by_handle(void *hanp, size_t hlen, void *buf, size_t bs);

       int attr_multi_by_handle(void   *hanp,  size_t  hlen,  void  *buf,  int
	      rtrvcnt, int flags);

       int attr_list_by_handle(void *hanp, size_t hlen, char *buf, size_t buf‐
	      siz, int flags, struct attrlist_cursor *cursor);

       int fssetdm_by_handle(void   *hanp,   size_t   hlen,  struct  fsdmidata
	      *fssetdm);

       void free_handle(void *hanp, size_t hlen);

       int getparents_by_handle(void *hanp, size_t hlen, parent_t *buf, size_t
	      bufsiz,  parent_cursor_t	*cursor, unsigned int *count, unsigned
	      int *more);

       int getparentpaths_by_handle(void *hanp, size_t	hlen,  parent_t	 *buf,
	      size_t  bufsiz,  parent_cursor_t	*cursor,  unsigned int *count,
	      unsigned int *more);

DESCRIPTION
       These functions provide a way to perform certain filesystem  operations
       without	using a file descriptor to access filesystem objects. They are
       intended for use by a limited set of system utilities  such  as	backup
       programs. They are supported only by the XFS filesystem.	 Link with the
       libhandle library to access these functions.

       A handle, hanp, uniquely identifies a filesystem object	or  an	entire
       filesystem.   There  is	one  and  only	one  handle  per filesystem or
       filesystem object.  Handles consist of some number of bytes.  The  size
       of a handle (i.e. the number of bytes comprising it) varies by the type
       of handle and may vary for different objects of	the  same  type.   The
       content of a handle is opaque to applications.  Since handle sizes vary
       and their contents are opaque, handles are described by two quantities,
       a pointer (hanp) and a size (hlen).  The size, hlen, indicates the num‐
       ber of bytes in the handle which are pointed to by the pointer.

       The path_to_handle() function returns the handle for the	 object	 given
       by the path argument. If the final component of the path name is a sym‐
       bolic link, the handle returned is that of the link itself.

       The path_to_fshandle() function returns the handle for  the  filesystem
       in which the object given by the path argument resides.

       The  fd_to_handle()  function  returns the handle for the object refer‐
       enced by the fd argument, which must be a valid file descriptor.

       The handle_to_fshandle() function returns the handle for the filesystem
       in which the object referenced by the handle given by the hanp and hlen
       arguments resides.

       The open_by_handle() function opens a file descriptor  for  the	object
       referenced  by a handle.	 It is analogous and identical to open(2) with
       the exception of accepting handles instead of path names.

       The readlink_by_handle() function returns the contents  of  a  symbolic
       link referenced by a handle.

       The   attr_multi_by_handle()   function	 manipulates   multiple	  user
       attributes on a filesystem object.  It is analogous  and	 identical  to
       attr_multif(3)  except  that  a	handle	is specified instead of a file
       descriptor.

       The attr_list_by_handle()  function  returns  the  names	 of  the  user
       attributes  of  a  filesystem object.  It is analogous and identical to
       attr_listf(3) except that a handle  is  specified  instead  of  a  file
       descriptor.

       The  fssetdm_by_handle()	 function  sets the di_dmevmask and di_dmstate
       fields in an XFS on-disk inode. It is analogous to the  XFS_IOC_FSSETDM
       xfsctl(3) command, except that a handle is specified instead of a file.

       The  free_handle()  function  frees  the	 storage allocated for handles
       returned by the following functions:  path_to_handle(),	path_to_fshan‐
       dle(), fd_to_handle(), and handle_to_fshandle().

       The getparents_by_handle() function returns an array of parent_t struc‐
       tures for each hardlink to the inode represented by the	given  handle.
       The parent structure encodes the parent inode number, generation number
       and the basename of the link.  This  function  is  not  operational  on
       Linux.

       The  getparentpaths_by_handle()	function  is  identical to the getpar‐
       ents_by_handle() function except that instead of returning the basename
       it  returns  the path of the link up to the mount point.	 This function
       is also not operational on Linux.

RETURN VALUE
       The function free_handle() has no failure indication. The  other	 func‐
       tions return the value 0 to the calling process if they succeed; other‐
       wise, they return the value -1 and set errno to indicate the error.

ERRORS
       EACCES Search permission was denied for a component of path.

       EBADF  fd is not a valid and open file descriptor.

       EFAULT An argument pointed to an invalid address.

       EINVAL path is in a filesystem that does not support these functions.

       ELOOP  Too many symbolic links were encountered in translating the path
	      name.

       ENAMETOOLONG
	      A	 component  of	path  or  the  entire  length  of path exceeds
	      filesystem limits.

       ENOENT A component of path does not exist.

       EPERM  The caller does not have sufficient privileges.

SEE ALSO
       open(2), readlink(2), attr_multi(3), attr_list(3), xfsctl(3), xfs(5).

								     HANDLE(3)
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