On Tue, Feb 24, 2009 at 6:33 PM, John Robinson
<john.robinson@xxxxxxxxxxxxxxxx> wrote:
> On 23/02/2009 20:16, NeilBrown wrote:
>>
>> On Tue, February 24, 2009 6:53 am, Doug Ledford wrote:
>>>
>>> Is XFS the only one that does the journal recovery on initial mount
>>> read-only during the initfs step, or do other journaled fses do the same
>>> thing? I didn't think ext3 recovered the journal until you switch to a
>>> read-write mount, but I guess I could be wrong.
>>
>> This from fs/ext3/super.c
>>
>> if (EXT3_HAS_INCOMPAT_FEATURE(sb, EXT3_FEATURE_INCOMPAT_RECOVER)) {
>> if (sb->s_flags & MS_RDONLY) {
>> printk(KERN_INFO "EXT3-fs: INFO: recovery "
>> "required on readonly
>> filesystem.\n");
>> if (really_read_only) {
>> printk(KERN_ERR "EXT3-fs: write access "
>> "unavailable, cannot proceed.\n");
>> return -EROFS;
>> }
>> printk (KERN_INFO "EXT3-fs: write access will "
>> "be enabled during recovery.\n");
>> }
>> }
>>
>> suggests that, unfortunately, you are.
>
> Presumably it's not only me that thinks this is insane? If I want to mount a
> filesystem read-only, I expect it to be mounted read-only; perhaps I already
> know it's damaged, or know the journal's damaged...
>
> I guess I can see the journal recovery normally being the right thing, and
> it is the filesystem we asked to have read-only not the disc, but still
> there surely has to be a way of saying mount without journal recovery, or
> mount without writing to disc, or both, and if there isn't who do I ask to
> implement it? (I'm way too rusty as a coder to trust myself to get it even
> half right.)
>
> I wonder: in the case of ext3 can I mount it as ext2 and thereby have the
> journal ignored rather than recovered? And would this be sufficient for the
> initrd context?
>
> Cheers,
I'm most familiar with xfs. It has a norecovery flag you can use with mount.
I believe it was introduced many years ago because LVM snapshots at
the time were truly read-only and it was not possible to replay
portions of the journal in order to mount a filesystem.
I would assume all filesystems received similar enhancements? Less
critical today because device mapper supports read/write snapshots.
Unfortunately, per the mount man page I only see that xfs has the
specific flag I'm talking about.
Greg
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