On Wed, Oct 07, 2015 at 03:29:55PM +0200, Jan Kara wrote:
> On Wed 30-09-15 09:36:35, Darrick J. Wong wrote:
> > On Wed, Sep 30, 2015 at 10:41:26AM +0200, Jan Kara wrote:
> > > On Mon 28-09-15 15:36:26, Darrick J. Wong wrote:
> > > > The ext2 mount code never checks the compat features against the ones
> > > > it knows about. This is correct behavior since compat features are
> > > > supposed to be rw-compatible with old drivers; however, for certain
> > > > configurations (journalled rootfs) we probably want the ext4 driver
> > > > to load, not ext2.
> > > >
> > > > Reported-by: Dave Chinner <david@xxxxxxxxxxxxx>
> > > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > >
> > > Isn't this a bit too harsh? I agree we should at least warn (and that's
> > > probably regardless of EXT4 config option) but just refusing mount looks
> > > too much to me...
> >
> > I admit that refusing the mount might be a bit much; the goal here was
> > merely to make it so that if the FS has a journal and ext4 was turned on,
> > hopefully ext2 rejects the mount and ext4 will probe it next.
> >
> > <shrug>
>
> OK, after some more thought about this I agree that your solution is
> probably the best. I'd say it's exceedingly rare that someone would like to
> mount ext3 filesystem using ext2 driver when he has ext4 available.
> Definitely more rare than someone wanting to mount clean ext3 filesystem
> and unexpectedly using ext2 driver for that. So my:
Now that I've thought about it more, I don't think that it's a good idea to
forever forbid mounting ext3 on ext2.ko. I'll send a patch to change the
default probing order along with an advisory to specify rootfstype= if you
compile both ext4 and ext2 and want specifically ext2 to drive.
That said, I still think that it's rare that anyone would really want to mount
ext3 with ext2.ko other than perhaps as a desperate last resort to get data off
the filesystem. Perhaps this patch will turn into something requiring readonly
mounting if ext4 was built and has_journal is on... after changing the default
probe order.
--D
>
> Acked-by: Jan Kara <jack@xxxxxxxx>
>
> Ted, can you please pick up the patch? Thanks!
>
> Honza
> > > > ---
> > > > fs/ext2/ext2.h | 6 +++++-
> > > > fs/ext2/super.c | 13 ++++++++++---
> > > > 2 files changed, 15 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/fs/ext2/ext2.h b/fs/ext2/ext2.h
> > > > index 8d15feb..ce508b1 100644
> > > > --- a/fs/ext2/ext2.h
> > > > +++ b/fs/ext2/ext2.h
> > > > @@ -547,7 +547,11 @@ struct ext2_super_block {
> > > > #define EXT2_FEATURE_INCOMPAT_META_BG 0x0010
> > > > #define EXT2_FEATURE_INCOMPAT_ANY 0xffffffff
> > > >
> > > > -#define EXT2_FEATURE_COMPAT_SUPP EXT2_FEATURE_COMPAT_EXT_ATTR
> > > > +#define EXT2_FEATURE_COMPAT_SUPP (EXT2_FEATURE_COMPAT_DIR_PREALLOC| \
> > > > + EXT2_FEATURE_COMPAT_IMAGIC_INODES| \
> > > > + EXT2_FEATURE_COMPAT_EXT_ATTR| \
> > > > + EXT2_FEATURE_COMPAT_RESIZE_INO| \
> > > > + EXT2_FEATURE_COMPAT_DIR_INDEX)
> > > > #define EXT2_FEATURE_INCOMPAT_SUPP (EXT2_FEATURE_INCOMPAT_FILETYPE| \
> > > > EXT2_FEATURE_INCOMPAT_META_BG)
> > > > #define EXT2_FEATURE_RO_COMPAT_SUPP (EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER| \
> > > > diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> > > > index 900e19c..4efb018 100644
> > > > --- a/fs/ext2/super.c
> > > > +++ b/fs/ext2/super.c
> > > > @@ -896,6 +896,16 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> > > > * previously didn't change the revision level when setting the flags,
> > > > * so there is a chance incompat flags are set on a rev 0 filesystem.
> > > > */
> > > > +#ifdef CONFIG_EXT4_FS
> > > > + /* Journalled FS should mount with ext4 if it's available */
> > > > + features = EXT2_HAS_COMPAT_FEATURE(sb, ~EXT2_FEATURE_COMPAT_SUPP);
> > > > + if (features) {
> > > > + ext2_msg(sb, KERN_ERR, "error: won't mount because of "
> > > > + "unsupported optional features (%x); try ext4",
> > > > + le32_to_cpu(features));
> > > > + goto failed_mount;
> > > > + }
> > > > +#endif
> > > > features = EXT2_HAS_INCOMPAT_FEATURE(sb, ~EXT2_FEATURE_INCOMPAT_SUPP);
> > > > if (features) {
> > > > ext2_msg(sb, KERN_ERR, "error: couldn't mount because of "
> > > >
> > > --
> > > Jan Kara <jack@xxxxxxxx>
> > > SUSE Labs, CR
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> > > the body of a message to majordomo@xxxxxxxxxxxxxxx
> > > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> > the body of a message to majordomo@xxxxxxxxxxxxxxx
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> --
> Jan Kara <jack@xxxxxxxx>
> SUSE Labs, CR
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
