HANDLE(3)

NAME
path_to_handle, path_to_fshandle, handle_to_fshandle, open_by_handle, readlink_by_handle, attr_multi_by_handle, attr_list_by_handle, fssetdm_by_handle, free_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 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 bufsiz,
                         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);

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 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 and a size. The size indicates the number 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 symbolic 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 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_fshandle(), and handle_to_fshandle().

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

DIAGNOSTICS

The function free_handle() has no failure indication. The other functions return the value 0 to the calling process if they succeed; otherwise, they return the value -1 and set errno to indicate the error:

[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.