|
|
what?
=====
The following is an attempt to generate the paths of a file when
only its gfid is known.
To find the path of a directory, the symlink handle to the
directory maintained in the ".glusterfs" backend directory is
read. The symlink handle is generated using the gfid of the
directory. It (handle) contains the directory's name and parent
gfid, which are used to recursively construct the absolute path as
seen by the user from the mount point.
A similar approach cannot be used for a regular file or a symbolic
link since its hardlink handle, generated using its gfid, doesn't
contain its parent gfid and basename. So xattrs are set to store
the parent gfids and the number of hardlinks to a file or a
symlink having the same parent gfid. When an user/application
requests for the paths of a regular file or a symlink with
multiple hardlinks, using the parent gfids stored in the xattrs,
the paths of the parent directories are generated as mentioned
earlier. The base names of the hardlinks (with the same parent
gfid) are determined by matching the actual backend inode numbers
of each entry in the parent directory with that of the hardlink
handle.
Xattr is set on a regular file, link, and symbolic link as
follows, Xattr name : trusted.pgfid.<pargfidstr> Xattr value :
<number of hardlinks to a regular file/symlink with the same
parentgfid>
If a regular file, hard link, symbolic link is created then an
xattr in the above format is set in the backend.
how to use?
===========
This functionality can be used through getxattr interface. Two
keys - glusterfs.ancestry.dentry and glusterfs.ancestry.path - enable
usage of this functionality. A successful getxattr will have the
result stored under same keys. Values will be,
glusterfs.ancestry.dentry:
--------------------------
A linked list of gf-dirent structures for all possible paths from
root to this gfid. If there are multiple paths, the linked-list
will be a series of paths one after another. Each path will be a
series of dentries representing all components of the path. This
key is primarily for internal usage within glusterfs.
glusterfs.ancestry.path:
------------------------
A string containing all possible paths from root to this gfid.
Multiple hardlinks of a file or a symlink are displayed as a colon
seperated list (this could interfere with path components
containing ':').
e.g. If there is a file "file1" in root directory with two hardlinks,
"/dir2/link2tofile1" and "/dir1/link1tofile1", then
[root@alpha gfsmntpt]# getfattr -n glusterfs.ancestry.path -e text
file1
glusterfs.ancestry.path="/file1:/dir2/link2tofile1:/dir1/link1tofile1"
Thanks Amar, Avati and Venky for the inputs.
Original Author: Ramana Raja <rraja@redhat.com>
BUG: 990028
Signed-off-by: Raghavendra G <rgowdapp@redhat.com>
Change-Id: I0eaa9101e333e0c1f66ccefd9e95944dd4a27497
Reviewed-on: http://review.gluster.org/5951
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>
|
