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Re: [PATCH] xfsrestore: fix multi stream support

To: Eric Sandeen <sandeen@xxxxxxxxxxx>
Subject: Re: [PATCH] xfsrestore: fix multi stream support
From: Rich Johnston <rjohnston@xxxxxxx>
Date: Wed, 2 Oct 2013 15:03:02 -0500
Cc: xfs-oss <xfs@xxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <524C68C5.2030202@xxxxxxxxxxx>
References: <524AF8AE.5030300@xxxxxxx> <524C68C5.2030202@xxxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0


On 10/02/2013 01:41 PM, Eric Sandeen wrote:
Ok me again.  ;)  Here's a testcase:

#!/bin/bash

# paths to binaries under test
DUMP=/mnt/test2/git/xfsdump/dump/xfsdump
RESTORE=/mnt/test2/git/xfsdump/restore/xfsrestore

# dir we'll create files in & dump
DUMPDIR=/mnt/test
# dir where we'll restore
RESTOREDIR=/mnt/test2/restore

mkdir -p $DUMPDIR/dir
mkdir -p $RESTOREDIR
rm -rf $DUMPDIR/dir/*
rm -rf $RESTOREDIR/*

truncate --size=1t $DUMPDIR/dir/sparsefile1
truncate --size=1t $DUMPDIR/dir/sparsefile2
truncate --size=1t $DUMPDIR/dir/sparsefile3
truncate --size=1t $DUMPDIR/dir/sparsefile4

rm -f stream1 stream2
$DUMP -L session -M label1 -M label2 -f stream1 -f stream2 $DUMPDIR
$RESTORE -F -f stream1 -f stream2 $RESTOREDIR

---

so we go down this path:

restore_extent_group
        <loop over extent headers adding up restoredsz>
         if (bstatp->bs_size > restoredsz) {
                 partial_reg()

In that loop, if we find DATA or HOLE, it advances "restoredsz" so it
generally does handle sparse files properly.

But a wholly sparse file has only the LAST header type, and resetoredsz
never moves.  This is important.  ;)  That's why the condition necessary
to go to partial_reg() is true.

in partial_reg(), with multiple streams, we check persp->a.parrest[i].is_ino
for each stream ("i") to see if the inode we're restoring i in any is_ino:

         /* Search for a matching inode.  Gaps can exist so we must search
          * all entries.
          */
         for (i=0; i < partialmax; i++ ) {
                 if (persp->a.parrest[i].is_ino == ino) {
                         isptr = &persp->a.parrest[i];
                         break;
                 }
         }

If this is the first time we've hit this inode we won't find it, and so we fill
it in on one slot:

         /* If not found, find a free one, fill it in and return */
         if ( ! isptr ) {
                 /* find a free one */
                 for (i=0; i < partialmax; i++ ) {
                         if (persp->a.parrest[i].is_ino == 0) {
                                 isptr->is_ino = ino;
                                <snip>
                                 goto found;
                         }
                 }
                 /* Should never get here. */
                 pi_unlock();
                 mlog( MLOG_NORMAL | MLOG_WARNING, _(
                   "partial_reg: Out of records. Extend attrs applied 
early.\n"));
#ifdef DEBUGPARTIALS
        }

Otherwise, we go to found:  which calls partial_check2().

So the only way we can not "find a free one" is if every a.parrest[i].is_ino
is set to something.  Well, we only have a few of them based on the number of
streams; what clears it?  partial_check2(), which is looking to see if the file
is wholly restored:

         /* Check if all bytes are accounted for.  */
         if (curoffset >= fsize) {
                 isptr->is_ino = 0;  /* clear the entry */

But since the wholly-sparse file had only a LAST record, and no HOLE, nothing
advanced, and it doesn't look "done" - so partial_check2() fails, we fill all
the slots, and we hit the dreaded "partial_reg: Out of records."

Bleah.

So I agree, this does seem to only happen with wholly-sparse files.

Adding a HOLE record for them would fix it, but that doesn't fix old dumps.

So I thought about doing something like this:


[PATCH] xfsdump: handle large, wholly-sparse files

In restore_extent_group(), we loop over all extent headers for an inode
in the stream, and add up the cumulatively restored size, accounting
for both HOLE and DATA records and advancing restoredsz as we go.

But for a wholly-sparse file, we have no HOLE header, only
a LAST header, and restoredsz remains at 0.

This makes it look like it's a partially-restored file, split
across streams because the final restoredsz for this stream is
less than the file size, and we go to partial_reg(), which
allocates one slot in persp->a.parrest[] for this inode.  But
we've also called partial_reg() with offset/sz of 0/0, which is
less than the file size so this inode never looks "done."

Normally partial_check2() would clear the persp->a.parrest[]
slot in the array when the file is fully restored, but in
this case, that is never satisfied.  So all stream slots
get filled as we encounter more inodes like this, and we
eventually get:

"partial_reg: Out of records. Extend attrs applied early."

Fix this by recognizing that if we hit a LAST header with
no restoredsz set (i.e. the LAST header is the only header),
set restoredsz to EOF (bstatp->bs_size) to indicate that
restoration of this file is complete, skip the call to
partial_reg(), and all is well.

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---

diff --git a/restore/content.c b/restore/content.c
index 54d933c..8949a7e 100644
--- a/restore/content.c
+++ b/restore/content.c
@@ -7516,6 +7516,11 @@ restore_extent_group( drive_t *drivep,
                 * we are done.
                 */
                if ( ehdr.eh_type == EXTENTHDR_TYPE_LAST ) {
+                       /* For a wholly sparse file, there is no HOLE
+                        * record; advance restoredsz to EOF.
+                        */
+                       if (!restoredsz)
+                               restoredsz = bstatp->bs_size;
                        break;
                }


So, ok, fine - that's essentially what your patch did.  ;)  But
now I understand it, and the above to me seems to keep more in  line
with the original logic, for better or worse.

What ,do you think?

Sure go for it. That was one of my test programs but obviously I choose the wrong one. ;) Its really sixes to me.

I still think the the check in partial_reg is not needed. I never saw a case where single stream restore hits that check except when there are no extents. Do you have an case/example?

We saw this issue with DMF offline files because DMF removes the extents and the file has an attribute which is not restored with the current code using multistream.

So I thinks a simple test case is:

Create a file with no extents.
Give that file an attribute
dump and restore it (both single and multistream)
verify the file still has the attribute.

Your thoughts?
--Rich


-Eric


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