www.LinuxHowtos.org

HANDLE

Section: C Library Functions (3)
Index Return to Main Contents

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_handle, 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 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);
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 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 fd_to_handle() function returns the handle for the object referenced 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_fshandle(), fd_to_handle(), and handle_to_fshandle().

The getparents_by_handle() function returns an array of parent_t structures 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 getparents_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 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.

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.