man/man3/handle.3

.TH HANDLE 3
.SH 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
.SH C SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <xfs/handle.h>
.HP
.BI "int\ path_to_handle(char *" path ", void **" hanp ", size_t *" hlen );
.HP
.BI "int\ path_to_fshandle(char *" path ", void **" hanp ", size_t *" hlen );
.HP
.BI "int\ fd_to_handle(int " fd ", void **" hanp ", size_t *" hlen );
.HP
.BI "int\ handle_to_fshandle(void *" hanp ", size_t " hlen ", void **" fshanp ,
.BI "size_t *" fshlen );
.HP
.BI "int\ open_by_handle(void *" hanp ", size_t " hlen ", int " oflag );
.HP
.BI "int\ readlink_by_handle(void *" hanp ", size_t " hlen ", void *" buf ,
.BI "size_t " bs );
.HP
.BI "int\ attr_multi_by_handle(void *" hanp ", size_t " hlen ", void *" buf ,
.BI "int " rtrvcnt ", int " flags );
.HP
.BI "int\ attr_list_by_handle(void *" hanp ", size_t " hlen ", char *" buf ,
.BI "size_t " bufsiz ", int " flags ", struct attrlist_cursor *" cursor );
.HP
.BI "int\ fssetdm_by_handle(void *" hanp ", size_t " hlen ", struct fsdmidata"
.BI * fssetdm );
.HP
.BI "void\ free_handle(void *" hanp ", size_t " hlen );
.HP
.BI "int\ getparents_by_handle(void *" hanp ", size_t " hlen ", parent_t *" buf ,
.BI "size_t " bufsiz ", parent_cursor_t *" cursor ", unsigned int *" count ,
.BI "unsigned int *" more );
.HP
.BI "int\ getparentpaths_by_handle(void *" hanp ", size_t " hlen ", parent_t"
.BI * buf ", size_t " bufsiz ", parent_cursor_t *" cursor ", unsigned int "
.BI * count ", unsigned int *" more );
.SH 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
.B libhandle
library to access these functions.
.PP
A handle,
.IR 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
.RI ( hanp ") and a size (" hlen ).
The size,
.IR hlen ,
indicates the number of bytes in the handle which are pointed to by the pointer.
.PP
The
.BR path_to_handle ()
function returns the handle for the object given by the
.I path
argument. If the final component of the path name is a symbolic link,
the handle returned is that of the link itself.
.PP
The
.BR path_to_fshandle ()
function returns the handle for the filesystem in which the object given by the
.I path
argument resides.
.PP
The
.BR fd_to_handle ()
function returns the handle for the object referenced by the
.I fd
argument, which must be a valid file descriptor.
.PP
The
.BR handle_to_fshandle ()
function returns the handle for the filesystem in which the object
referenced by the handle given by the
.I hanp
and
.I hlen
arguments resides.
.PP
The
.BR open_by_handle ()
function opens a file descriptor for the object referenced by a handle.
It is analogous and identical to
.BR open (2)
with the exception of accepting handles instead of path names.
.PP
The
.BR readlink_by_handle ()
function returns the contents of a symbolic link referenced by a handle.
.PP
The
.BR attr_multi_by_handle ()
function manipulates multiple user attributes on a filesystem object.
It is analogous and identical to
.BR attr_multif (3)
except that a handle is specified instead of a file descriptor.
.PP
The
.BR attr_list_by_handle ()
function returns the names of the user attributes of a filesystem object.
It is analogous and identical to
.BR attr_listf (3)
except that a handle is specified instead of a file descriptor.
.PP
The
.BR fssetdm_by_handle ()
function sets the
.B di_dmevmask
and
.B di_dmstate
fields in an XFS on-disk inode. It is analogous to the
.BR "XFS_IOC_FSSETDM xfsctl" (3)
command, except that a handle is specified instead of a file.
This function is not supported on Linux.
.PP
The
.BR free_handle ()
function frees the storage allocated for handles returned by the following
functions:
.BR path_to_handle (),
.BR path_to_fshandle (),
.BR fd_to_handle (),
and
.BR handle_to_fshandle ().
.PP
The
.BR getparents_by_handle ()
function returns an array of
.B 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.
.B This function is not operational on Linux.
.PP
The
.BR getparentpaths_by_handle ()
function is identical to the
.BR getparents_by_handle ()
function except that instead of returning the basename it returns the path
of the link up to the mount point.
.B This function is also not operational on Linux.
.SH RETURN VALUE
The function
.BR 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
.I errno
to indicate the error.
.SH ERRORS
.TP
.B EACCES
Search permission was denied for a component of
.IR path .
.TP
.B EBADF
.I fd
is not a valid and open file descriptor.
.TP
.B EFAULT
An argument pointed to an invalid address.
.TP
.B EINVAL
.I path
is in a filesystem that does not support these functions.
.TP
.B ELOOP
Too many symbolic links were encountered in translating the path name.
.TP
.B ENAMETOOLONG
A component of
.I path
or the entire length of
.I path
exceeds filesystem limits.
.TP
.B ENOENT
A component of
.I path
does not exist.
.TP
.B EPERM
The caller does not have sufficient privileges.
.SH SEE ALSO
.BR open (2),
.BR readlink (2),
.BR attr_multi (3),
.BR attr_list (3),
.BR xfsctl (3),
.BR xfs (5).