Re: [PATCH 1/2] xfs_db: support the needsrepair feature flag in the version command

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Feb 03, 2021 at 08:07:21AM -0500, Brian Foster wrote:
> On Tue, Feb 02, 2021 at 01:09:15PM -0800, Darrick J. Wong wrote:
> > On Tue, Jan 19, 2021 at 09:37:14AM -0500, Brian Foster wrote:
> > > On Fri, Jan 15, 2021 at 05:24:47PM -0800, Darrick J. Wong wrote:
> > > > From: Darrick J. Wong <djwong@kernel.org>
> > > > 
> > > > Teach the xfs_db version command about the 'needsrepair' flag, which can
> > > > be used to force the system administrator to repair the filesystem with
> > > > xfs_repair.
> > > > 
> > > > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > > > ---
> > > >  db/check.c           |    5 ++
> > > >  db/sb.c              |  153 ++++++++++++++++++++++++++++++++++++++++++++++++--
> > > >  db/xfs_admin.sh      |   10 ++-
> > > >  man/man8/xfs_admin.8 |   15 +++++
> > > >  man/man8/xfs_db.8    |    5 ++
> > > >  5 files changed, 178 insertions(+), 10 deletions(-)
> > > > 
> > > > 
> ...
> > > > diff --git a/db/sb.c b/db/sb.c
> > > > index d09f653d..fcc2a0ed 100644
> > > > --- a/db/sb.c
> > > > +++ b/db/sb.c
> ...
> > > > @@ -717,8 +836,23 @@ version_f(
> > > >  			return 0;
> > > >  		}
> > > >  
> > > > +		if (xfs_sb_version_needsrepair(&mp->m_sb)) {
> > > > +			dbprintf(_("%s: filesystem needs xfs_repair\n"),
> > > > +				progname);
> > > > +			return 0;
> > > > +		}
> > > > +
> > > >  		/* Logic here derived from the IRIX xfs_chver(1M) script. */
> > > > -		if (!strcasecmp(argv[1], "extflg")) {
> > > > +		if (!strcasecmp(argv[1], "needsrepair")) {
> > > > +			if (!xfs_sb_version_hascrc(&mp->m_sb)) {
> > > > +				dbprintf(
> > > > +		_("needsrepair flag cannot be enabled on pre-V5 filesystems\n"));
> > > > +				exitcode = 2;
> > > > +				return 1;
> > > 
> > > Hmm.. I see that exitcode 1 means error && xfs_repair while exitcode 2
> > > means error && !xfs_repair, but I'm still not sure I follow the high
> > > level error semantics, particularly if we happen to fail updating
> > > secondary supers. I wonder if it would be more straightforward to have
> > > xfs_db only return an error when an update attempt occurs and fails and
> > > then let xfs_admin run xfs_repair if status == 0 && NEEDSREPAIR is set.
> > 
> > Hm.  I'd be even more tempted to make it run if xfs_db just failed.
> > 
> > > I suppose the various other ".. bit already set" or "v5 super required"
> > > conditions don't really need to be errors and thus repair would only run
> > > in those cases if NEEDSREPAIR was still set on the fs. Otherwise if
> > > xfs_db fails we dump an error message and encourage the user to run
> > > xfs_repair themselves.
> > 
> > Yeah, that does seem more reasonable.  I'll change xfs_admin to force a
> > run through repair if the NEEDSREPAIR feature is set or if the xfs_db
> > command failed, since that probably means something's wrong with the fs.
> > 
> 
> Perhaps, or the storage if an I/O happens to fail or something. I'm not
> sure we should go that route where if the version upgrade happens to
> fail we do a "well this operation failed, but something is probably
> wrong so let me try and repair that for you." I'd personally be kind of
> annoyed by that if I didn't have an opportunity to analyze the problem
> before making the decision to run a (potentially destructive) repair
> operation. I agree it's an unlikely situation, but IMO the automatically
> invoked repair should be isolated to the specific case that warrants it
> and everything else should probably just bail out.

Hm, good point, considering how long it can take to run repair.  I'm
sure there's some sysadmin out there who would actually prefer to nuke
the whole fs/node if the upgrade fails.

> The user really doesn't need to know or care that a repair is involved
> in the first place, so ISTM that either "upgrade operation succeeded" or
> "upgrade operation failed, fs has problems" is fairly expected failure
> handling behavior (as opposed to allowing things like "upgrade operation
> failed, we ran repair anyways and fixed some other stuff, maybe try that
> upgrade again since the last one basically just invoked xfs_repair?").
> If we really wanted to be careful, we could even run a repair -n first
> and require it succeed before attempting to touch the superblock. That
> might be annoying in cases where repair takes forever, but at least if
> the user bails on it it would likely be before we've modified anything.

...or make it more likely that the user ^Cs and never uses our
scurrilous upgrader tool. :)

I dunno, I've a slight preference for /knowing/ that the fs isn't a
crazy tangle of crap before we try to upgrade it.  Though as I've
mentioned before, resize2fs has weird heuristics to guesstimate if a
filesystem is clean "enough", and ext4 even tracks the last fsck and
mount times.  I don't really want to go down that path.

Perhaps we should simply document xfs_repair -n as a preparation step?

--D

> 
> Brian
> 
> > > There are still corner cases I guess, but that does _seem_ a bit more
> > > elegant to me. Otherwise I suppose a comment somewhere that explains
> > > when/why to use which error code would be helpful.
> > 
> > <nod> I'll put them in.
> > 
> > --D
> > 
> > > Brian
> > > 
> > > > +			}
> > > > +
> > > > +			v5features.incompat |= XFS_SB_FEAT_INCOMPAT_NEEDSREPAIR;
> > > > +		} else if (!strcasecmp(argv[1], "extflg")) {
> > > >  			switch (XFS_SB_VERSION_NUM(&mp->m_sb)) {
> > > >  			case XFS_SB_VERSION_1:
> > > >  				version = 0x0004 | XFS_SB_VERSION_EXTFLGBIT;
> > > > @@ -809,6 +943,11 @@ version_f(
> > > >  			mp->m_sb.sb_versionnum = version;
> > > >  			mp->m_sb.sb_features2 = features;
> > > >  		}
> > > > +
> > > > +		if (!upgrade_v5_features(mp, &v5features)) {
> > > > +			exitcode = 1;
> > > > +			return 1;
> > > > +		}
> > > >  	}
> > > >  
> > > >  	if (argc == 3) {	/* VERSIONNUM + FEATURES2 */
> > > > diff --git a/db/xfs_admin.sh b/db/xfs_admin.sh
> > > > index bd325da2..0e79bbf9 100755
> > > > --- a/db/xfs_admin.sh
> > > > +++ b/db/xfs_admin.sh
> > > > @@ -7,9 +7,9 @@
> > > >  status=0
> > > >  DB_OPTS=""
> > > >  REPAIR_OPTS=""
> > > > -USAGE="Usage: xfs_admin [-efjlpuV] [-c 0|1] [-L label] [-U uuid] device [logdev]"
> > > > +USAGE="Usage: xfs_admin [-efjlpuV] [-c 0|1] [-L label] [-U uuid] [-O v5_feature] device [logdev]"
> > > >  
> > > > -while getopts "efjlpuc:L:U:V" c
> > > > +while getopts "efjlpuc:L:O:U:V" c
> > > >  do
> > > >  	case $c in
> > > >  	c)	REPAIR_OPTS=$REPAIR_OPTS" -c lazycount="$OPTARG;;
> > > > @@ -19,6 +19,9 @@ do
> > > >  	l)	DB_OPTS=$DB_OPTS" -r -c label";;
> > > >  	L)	DB_OPTS=$DB_OPTS" -c 'label "$OPTARG"'";;
> > > >  	p)	DB_OPTS=$DB_OPTS" -c 'version projid32bit'";;
> > > > +	O)	DB_OPTS=$DB_OPTS" -c 'version "$OPTARG"'";
> > > > +		# Force repair to run by adding a single space to REPAIR_OPTS
> > > > +		REPAIR_OPTS="$REPAIR_OPTS ";;
> > > >  	u)	DB_OPTS=$DB_OPTS" -r -c uuid";;
> > > >  	U)	DB_OPTS=$DB_OPTS" -c 'uuid "$OPTARG"'";;
> > > >  	V)	xfs_db -p xfs_admin -V
> > > > @@ -34,6 +37,7 @@ set -- extra $@
> > > >  shift $OPTIND
> > > >  case $# in
> > > >  	1|2)
> > > > +		status=0
> > > >  		# Pick up the log device, if present
> > > >  		if [ -n "$2" ]; then
> > > >  			DB_OPTS=$DB_OPTS" -l '$2'"
> > > > @@ -46,7 +50,7 @@ case $# in
> > > >  			eval xfs_db -x -p xfs_admin $DB_OPTS $1
> > > >  			status=$?
> > > >  		fi
> > > > -		if [ -n "$REPAIR_OPTS" ]
> > > > +		if [ -n "$REPAIR_OPTS" ] && [ $status -ne 2 ]
> > > >  		then
> > > >  			# Hide normal repair output which is sent to stderr
> > > >  			# assuming the filesystem is fine when a user is
> > > > diff --git a/man/man8/xfs_admin.8 b/man/man8/xfs_admin.8
> > > > index 8afc873f..b423981d 100644
> > > > --- a/man/man8/xfs_admin.8
> > > > +++ b/man/man8/xfs_admin.8
> > > > @@ -6,6 +6,8 @@ xfs_admin \- change parameters of an XFS filesystem
> > > >  [
> > > >  .B \-eflpu
> > > >  ] [
> > > > +.BI \-O " feature"
> > > > +] [
> > > >  .BR "\-c 0" | 1
> > > >  ] [
> > > >  .B \-L
> > > > @@ -103,6 +105,19 @@ The filesystem label can be cleared using the special "\c
> > > >  " value for
> > > >  .IR label .
> > > >  .TP
> > > > +.BI \-O " feature"
> > > > +Add a new feature to the filesystem.
> > > > +Only one feature can be specified at a time.
> > > > +Features are as follows:
> > > > +.RS 0.7i
> > > > +.TP
> > > > +.B needsrepair
> > > > +If this is a V5 filesystem, flag the filesystem as needing repairs.
> > > > +Until
> > > > +.BR xfs_repair (8)
> > > > +is run, the filesystem will not be mountable.
> > > > +.RE
> > > > +.TP
> > > >  .BI \-U " uuid"
> > > >  Set the UUID of the filesystem to
> > > >  .IR uuid .
> > > > diff --git a/man/man8/xfs_db.8 b/man/man8/xfs_db.8
> > > > index 58727495..7331cf19 100644
> > > > --- a/man/man8/xfs_db.8
> > > > +++ b/man/man8/xfs_db.8
> > > > @@ -971,6 +971,11 @@ may toggle between
> > > >  and
> > > >  .B attr2
> > > >  at will (older kernels may not support the newer version).
> > > > +The filesystem can be flagged as requiring a run through
> > > > +.BR xfs_repair (8)
> > > > +if the
> > > > +.B needsrepair
> > > > +option is specified and the filesystem is formatted with the V5 format.
> > > >  .IP
> > > >  If no argument is given, the current version and feature bits are printed.
> > > >  With one argument, this command will write the updated version number
> > > > 
> > > 
> > 
>