[patch] nmount ro, rw and negated option handling
Aurelien Jarno
aurelien at aurel32.net
Sun Jan 23 10:16:33 UTC 2011
On Fri, Jan 14, 2011 at 02:24:54PM +0200, Jaakko Heinonen wrote:
>
> Hi,
Hi,
> Currently nmount(2) allows a mount point to have "ro", "rw", and "noro"
> string options concurrently active. This can cause erratic behavior
> demonstrated by this example:
>
> 1. Have mountd(8) running.
> 2. # mdconfig -a -t vnode -f ufsimg
> 3. # mount -o ro,rw /dev/md0 /mnt
>
> After these steps the mount point has string options "ro", "rw" and
> "noro" active but the MNT_RDONLY flag is not set. Eventually this will
> lead to "ffs_sync: rofs mod" (or similar) panic because the ffs code
> marks the file system read-only due to the "ro" string option.
> (MNT_RDONLY flag is used in most places for read-only check.)
>
> I wrote a patch to do following changes:
>
> - vfs_equalopts() now recognizes "ro" and "rw" as equal options
> - vfs_mergeopts() uses vfs_sanitizeopts() to merge options. This ensures
> that if the same option shows up several times (negated or not), only
> the last one is taken in account. There is still a problem when for
> example option "foo" and "nofoo" are merged: the "nofoo" option will
> become an active option. This is not a regression however and
> currently I don't know an easy way to solve this because the list of
> valid options is not available in vfs_mergeopts().
> - vfs_donmount() always converts "norw"/"rdonly" to "ro" and "noro" to
> "rw". Thus the mount point will always have either "rw" or "ro"
> option. I haven't seen any in-tree file system to test for "noro" but
> at least ZFS tests for "rw". That's why I chose "rw" instead or
> "noro".
>
> The patch is available here:
>
> http://people.freebsd.org/~jh/patches/nmount-ro-rw.diff
>
> Reviews and testing would be appreciated.
>
Thanks for the patch, I confirm it fixes the issue I reported in
kern/150206.
Aurelien
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurelien at aurel32.net http://www.aurel32.net
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