[PATCH] xfs_metadump: Make -F (force) optional

[Eric Sandeen <sandeen@xxxxxxxxxx>]

If we do something crazy like:

# xfs_metadump /root/anaconda.cfg outfile

xfs_metadump will pass "-F" to xfs_db to carry on even in the face
of bad superblock magic. [1]  Depending on what we gave as an input
file, we may very well fail quite badly:

> xfs_metadump: /root/anaconda.cfg is not a valid XFS filesystem (unexpected SB 
> magic number 0x230a2320)
> Floating point exception

I don't think it's possible to harden every path through libxfs for
non-xfs filesystems as input.  (Even if it's possible, I don't think it's
worth the effort).

So I propose making the "-F" optional; by default, xfs_metadump will
say no, this has bad magic, I'm stopping.  If the admin really wants to
try to proceed, suggest that they can use "-F" and they can keep all the
broken pieces.

[1] behavior added in 7f98455 xfs_db: exit on invalid magic number

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


diff --git a/db/init.c b/db/init.c
index 8f86f45..e7f536a 100644
--- a/db/init.c
+++ b/db/init.c
@@ -140,8 +140,10 @@ init(
        if (sbp->sb_magicnum != XFS_SB_MAGIC) {
                fprintf(stderr, _("%s: %s is not a valid XFS filesystem 
(unexpected SB magic number 0x%08x)\n"),
                        progname, fsdevice, sbp->sb_magicnum);
-               if (!force)
+               if (!force) {
+                       fprintf(stderr, _("Use -F to force a read attempt.\n"));
                        exit(EXIT_FAILURE);
+               }
        }
 
        mp = libxfs_mount(&xmount, sbp, x.ddev, x.logdev, x.rtdev,
diff --git a/db/xfs_metadump.sh b/db/xfs_metadump.sh
index 28b04b8..7ce7a6d 100755
--- a/db/xfs_metadump.sh
+++ b/db/xfs_metadump.sh
@@ -5,7 +5,7 @@
 
 OPTS=" "
 DBOPTS=" "
-USAGE="Usage: xfs_metadump [-efogwV] [-m max_extents] [-l logdev] source 
target"
+USAGE="Usage: xfs_metadump [-efFogwV] [-m max_extents] [-l logdev] source 
target"
 
 while getopts "efgl:m:owV" c
 do
@@ -17,6 +17,7 @@ do
        w)      OPTS=$OPTS"-w ";;
        f)      DBOPTS=$DBOPTS" -f";;
        l)      DBOPTS=$DBOPTS" -l "$OPTARG" ";;
+       F)      DBOPTS=$DBOPTS" -F";;
        V)      xfs_db -p xfs_metadump -V
                status=$?
                exit $status
@@ -29,7 +30,7 @@ done
 set -- extra $@
 shift $OPTIND
 case $# in
-       2)      xfs_db$DBOPTS -F -i -p xfs_metadump -c "metadump$OPTS $2" $1
+       2)      xfs_db$DBOPTS -i -p xfs_metadump -c "metadump$OPTS $2" $1
                status=$?
                ;;
        *)      echo $USAGE 1>&2
diff --git a/man/man8/xfs_metadump.8 b/man/man8/xfs_metadump.8
index 4fa1b1c..077fff5 100644
--- a/man/man8/xfs_metadump.8
+++ b/man/man8/xfs_metadump.8
@@ -4,7 +4,7 @@ xfs_metadump \- copy XFS filesystem metadata to a file
 .SH SYNOPSIS
 .B xfs_metadump
 [
-.B \-efgow
+.B \-efFgow
 ] [
 .B \-m
 .I max_extents
@@ -86,6 +86,11 @@ file option). This can also happen if an image copy of a 
filesystem has
 been made into an ordinary file with
 .BR xfs_copy (8).
 .TP
+.B \-F
+Specifies that we want to continue even if the superblock magic is not correct.
+If the source is truly not an XFS filesystem, the resulting image will be 
useless,
+and xfs_metadump may crash.
+.TP
 .B \-g
 Shows dump progress. This is sent to stdout if the
 .I target