Subject: Re: kern/30525: remounting ffs read-only (mount -ur) does not sync metadata
To: None <,,>
From: Darrin B.Jewell <>
List: netbsd-bugs
Date: 06/28/2005 19:23:01
The following reply was made to PR kern/30525; it has been noted by GNATS.

From: "Darrin B.Jewell" <>
Subject: Re: kern/30525: remounting ffs read-only (mount -ur) does not sync metadata
Date: 28 Jun 2005 15:22:07 -0400

 The following three recipies will reproduce this bug:
 Recipe 1, layer mount, courtesy dyoung@
   newfs /dev/rwd1a
   mount_ffs /dev/wd1a /mnt
   mkdir /mnt/foo
   mkdir /mnt/bar
   mount_null /mnt/foo /mnt/bar
   echo test > /mnt/bar/test1
   echo test > /mnt/bar/test2
   mount_ffs -o update,ro /dev/wd1a /mnt
 Recipe 2: reference to unlinked file, courtesy atatat@
   newfs /dev/rwd1a
   mount_ffs /dev/wd1a /mnt
   touch /mnt/file
   tail -f /mnt/file &
   rm /mnt/file
   mount_ffs -o update,ro /dev/wd1a /mnt
 Recipe 3: async mount, as per this pr.
   newfs /dev/rwd1a
   mount_ffs -o async /dev/wd1a /mnt
   echo test > /mnt/test
   mount_ffs -o update,ro /dev/wd1a /mnt
 At the time of remount, only files open for writing are synced.
 Unfortunately, each of the above cases have different reasons why
 there may be unflushed outstanding changes on files which are no
 longer open for writing.
 In case 1, layer mounts delay vnode inactivation until the vnode is
 reclaimed, allowing flushes to remain unsynced.
 In case 2, the unreferenced file needs to be handled similarly
 to a file open for writing.
 In case 3, async mounts delay inode updates indefinitely.
 Putting a simple ffs_sync call in the remount has a couple
 of minor problems, which need to be handled:
   - the readonly flag is already set on the mount point by
     that time, so the update call will be ignored.
   - referenced but unlinked files need to be inactivated
     rather than simply flushed.
   - ffs_sync skips over vnodes if it cannot get the vnode lock
     on first try, it probably shouldn't when MNT_WAIT
 These issues should be managable, I'll work on a fix.