Date: Tue, 12 Nov 1996 17:19:41 -0800 (PST) From: Archie Cobbs <archie@whistle.com> To: freebsd-hackers@freebsd.org Subject: kernel and/or fsck(8) bug Message-ID: <199611130119.RAA08629@bubba.whistle.com>
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Hello
We encountered an interesting situation where the superblock for
a file system got written to disk with the "fs_fmod" flag set to
one. It appears that this flag is normally supposed to be cleared
during ffs_sync(), but we experienced a crash, or some other weird
occurrence that left it on the disk set to 1.
Later this partition was mounted read-only... and the fs_fmod
field was never cleared, causing ffs_sync() to panic "rofs mod"
when trying to unmount that filesystem (ffs_vfsops.c: line 790).
Observation #1:
As far as I can tell, the meaning of this field is ``this copy of
the superblock has been modified from the real one on the disk.''
Therefore, the value of this field **in the actual superblock on
the disk** should either:
(a) ALWAYS be zero, in which case fsck(8) should be responsible
for checking/fixing it; or
(b) ALWAYS be ignored, in which case every time the superblock
is read from disk this field should be set to zero.
Observation #2:
Currently, the only place this field is actually *used* for anything
is to detect this panic condition. Presumably there is some intended
future use for it; if not, it should just be taken out!
Below are patches for both (a) and (b), either of which should
(hopefully) address the problem.
Thanks,
-Archie
___________________________________________________________________________
Archie Cobbs * Whistle Communications, Inc. * http://www.whistle.com
FSCK PATCH:
Index: pass5.c
===================================================================
RCS file: /cvs/freebsd/src/sbin/fsck/pass5.c,v
retrieving revision 1.5
diff -c -r1.5 pass5.c
*** 1.5 1995/05/30 06:09:06
--- pass5.c 1996/11/13 01:05:39
***************
*** 318,323 ****
--- 318,332 ----
fs->fs_fmod = 0;
sbdirty();
}
+ if (fs->fs_fmod != 0) {
+ pwarn("MODIFIED FLAG SET IN SUPERBLOCK");
+ if (preen)
+ printf(" (FIXED)\n");
+ if (preen || reply("FIX") == 1) {
+ fs->fs_fmod = 0;
+ sbdirty();
+ }
+ }
if (fs->fs_clean == 0) {
pwarn("CLEAN FLAG NOT SET IN SUPERBLOCK");
if (preen)
KERNEL PATCH:
Index: ffs_vfsops.c
===================================================================
RCS file: /cvs/freebsd/src/sys/ufs/ffs/ffs_vfsops.c,v
retrieving revision 1.41
diff -c -r1.41 ffs_vfsops.c
*** 1.41 1996/09/07 17:34:57
--- ffs_vfsops.c 1996/11/13 01:06:25
***************
*** 383,388 ****
--- 383,389 ----
if (error)
return (error);
fs = (struct fs *)bp->b_data;
+ fs->fs_fmod = 0;
if (fs->fs_magic != FS_MAGIC || fs->fs_bsize > MAXBSIZE ||
fs->fs_bsize < sizeof(struct fs)) {
brelse(bp);
***************
*** 506,511 ****
--- 507,513 ----
if (error)
goto out;
fs = (struct fs *)bp->b_data;
+ fs->fs_fmod = 0;
if (fs->fs_magic != FS_MAGIC || fs->fs_bsize > MAXBSIZE ||
fs->fs_bsize < sizeof(struct fs)) {
error = EINVAL; /* XXX needs translation */
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