Re: [PATCH] xfsdump: zero bs_forkoff, don't fill in the value

Ben Myers
2013-01-31T20:34:39Z

Hi Eric,

On Tue, Jan 08, 2013 at 11:31:41AM -0600, Eric Sandeen wrote:
> In xfsdump 3.1.2 I explicitly added the bs_forkoff member
> to this structure; I tried to be good and explicitly fill
> in a value. However, previously it was initialized to
> zero, (by virtue of being missing) and now we're giving it
> a value (which is ignored by restore, other than to checksum
> it).
>
> By putting in a non-zero value, I broke checksumming
> when an xfsdump with a non-zero forkoff was restored
> by an older xfsrestore that doesn't know about the field.
> Fill in 0 to fix backwards compatibility.
>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> Reported-by: Fugazzi99 <fugazzi99@gmail.com>
> ---
>
> diff --git a/dump/content.c b/dump/content.c
> index 9a36fe1..ac19021 100644
> --- a/dump/content.c
> +++ b/dump/content.c
> @@ -4928,7 +4928,7 @@ copy_xfs_bstat(bstat_t *dst, xfs_bstat_t *src)
> dst->bs_extents = src->bs_extents;
> dst->bs_gen = src->bs_gen;
> dst->bs_projid_lo = src->bs_projid_lo;
> - dst->bs_forkoff = src->bs_forkoff;
> + dst->bs_forkoff = 0;

I think I understand this now.

A legacy xfs_repair would not have bs_forkoff in

read_filehdr
xlate_filehdr
xlate_bstat
IXLATE(bs1, bs2, bs_forkoff);

And bs_pad is copied without any translation. This works fine as long as
bs_forkoff and bs_projid_hi are 0. In the failure case bs_forkoff was nonzero
and changed the checksum because it was not translated. I could not reproduce
the checksum failure on a filesystem without xattrs because bs_forkoff was
always 0.

*** Get set up with an xattr:

# touch /mnt/scratch/file
# setfattr -h -n user.testattr -v testvalue /mnt/scratch/file

*** Dump the filesystem with 3.1.2:

# xfsdump - /mnt/scratch > dump-with-attribute-and-3.1.2.out
xfsdump: using file dump (drive_simple) strategy
xfsdump: version 3.1.2 (dump format 3.0)
...
xfsdump: Dump Status: SUCCESS

*** Restore with 3.1.0, and print out bs_pad:

# xfsrestore -f dump-with-attribute-and-3.1.2.out /mnt/test
xfsrestore: using file dump (drive_simple) strategy
xfsrestore: version 3.1.0 (dump format 3.0) - type ^C for status and control
...
xfsrestore: reading directories
read_filehdr pad is 0 0 0 0 0 0 0 0 0 0 0 0 0 0
read_filehdr pad is 0 78 0 0 0 0 0 0 0 0 0 0 0 0
xfsrestore: WARNING: bad file header checksum
...
xfsrestore: Restore Status: INCOMPLETE

*** Restore with 3.1.0, translating bs_pad where bs_forkoff lives:

# xfsrestore -f dump-with-attribute-and-3.1.2.out /mnt/test
xfsrestore: using file dump (drive_simple) strategy
xfsrestore: version 3.1.0 (dump format 3.0) - type ^C for status and control
...
xfsrestore: reading directories
read_filehdr pad is 0 0 0 0 0 0 0 0 0 0 0 0 0 0
read_filehdr pad is 78 0 0 0 0 0 0 0 0 0 0 0 0 0
xfsrestore: 1 directories and 1 entries processed
xfsrestore: directory post-processing
xfsrestore: restoring non-directory files
read_filehdr pad is 78 0 0 0 0 0 0 0 0 0 0 0 0 0
read_filehdr pad is 0 0 0 0 0 0 0 0 0 0 0 0 0 0
xfsrestore: restore complete: 0 seconds elapsed
xfsrestore: Restore Summary:
xfsrestore: stream 0 /root/xfsdump/dump-with-attribute-and-3.1.2.out OK (success)
xfsrestore: Restore Status: SUCCESS

:!quilt di
Index: xfsdump/restore/content.c
===================================================================
--- xfsdump.orig/restore/content.c
+++ xfsdump/restore/content.c
@@ -8038,6 +8038,7 @@ read_filehdr( drive_t *drivep, filehdr_t
intgen_t nread;
intgen_t rval;
filehdr_t tmpfh;
+ int i;

nread = read_buf( ( char * )&tmpfh,
sizeof( *fhdrp ),
@@ -8078,6 +8079,16 @@ read_filehdr( drive_t *drivep, filehdr_t
"corrupt file header\n") );
return RV_CORRUPT;
}
+ i = bstatp->bs_pad[0];
+ bstatp->bs_pad[0] = bstatp->bs_pad[1];
+ bstatp->bs_pad[1] = i;
+
+ printf("%s pad is ", __func__);
+ for (i = 0; i < 14; i++) {
+ printf("%x ", bstatp->bs_pad[i]);
+ }
+ printf("\n");
+
if ( !is_checksum_valid( fhdrp, FILEHDR_SZ )) {
mlog( MLOG_NORMAL | MLOG_WARNING, _(
"bad file header checksum\n") );

Now all new dumps will have zeroed bs_pad[0,1] so it doesn't matter that they
aren't xlated. Your fix looks good.

Reviewed-by: Ben Myers <bpm@sgi.com>

I'll pull this in immediately.

Thanks,
Ben

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