On Thu, Oct 19, 2017 at 07:11:50AM +0300, Amir Goldstein wrote:
> On Thu, Oct 19, 2017 at 1:55 AM, Allison Henderson
> <allison.henderson@xxxxxxxxxx> wrote:
> > Hi all,
> >
> > This is the third version of parent pointer attributes for xfs.
> > I've integrated the suggestions made since v2, mostly moving the
> > attr buffers in the xfs_attr_log_item to pointers that point to
> > xfs_attr_item. I've also implementing the recovery routines for
> > the xfs_attr_log_format. If I missed anything please point it
> > out. As always, comments and feedback are appreciated. Thank
> > you!
> >
>
> A minor comment about the cover letter.
> All designated reviewers must know exactly what "parent pointers" are for,
> but it could be useful to add some context in the cover letter about the purpose
> of this work for the sake of other readers on the list. Useful to refer to the
> upcoming scrub support patches.
>
> BTW, not sure if this was mentioned in the previous lifetime of those
> patches, but parent pointers can be used to implement exportfs operation
> xfs_fs_fh_to_parent() for "non-connectable" file handles (FILEID_INO32_GEN)
> and to implement xfs_fs_get_name(), which would make reconnect_path()
> *much* more efficient.
However, XFS only uses FILEID_INO32_GEN for directories
because they have known parents. For them, we implement ->get_parent()
and that means reconnect_path just does ->lookup("..") to find the
parents and doesn't need anything special.
We use FILEID_INO32_GEN_PARENT for all other types of files to
encode the ino # + generation of the parent inode into the handle.
That means for any non-dir file handle, our implemention of
->fh_to_parent will get us the parent info as efficiently as
possible.
IOWs, parent pointers won't actually speed up filehandle ->
dentry reconnection on XFS at all because we already encode parent
pointers into the filehandles that need them....
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
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