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From: Joel Becker on 6 Jul 2010 16:10
[Added jbd2 Ccs. Sorry about the whole-patch-quote, but I want jbd2
folks to see what we're doing.]

On Tue, Jun 29, 2010 at 05:16:11PM -0700, Patrick J. LoPresti wrote:
> The OCFS2 developers have already done all of the hard work to allow
> volumes larger than 16 TiB. But there is still a "sanity check" in
> fs/ocfs2/super.c that prevents the mounting of such volumes, even when
> the cluster size and journal options would allow it.
>
> This patch replaces that sanity check with a more sophisticated one to
> mount a huge volume provided that (a) it is addressable by the raw
> word/address size of the system (borrowing a test from ext4); (b) the
> volume is using JBD2; and (c) the JBD2_FEATURE_INCOMPAT_64BIT flag is
> set on the journal.
>
> I factored out the sanity check into its own function. I also moved it
> from ocfs2_initialize_super() down to ocfs2_check_volume(); any earlier,
> and the journal's flags have not been read from disk yet.
>
> I have tested this patch on small volumes, huge volumes, and huge
> volumes without 64-bit block support in the journal. All of them appear
> to work or to fail gracefully, as appropriate.
>
> Signed-off-by: Patrick LoPresti <lopresti(a)gmail.com>
>
>
> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> index 0eaa929..3db233d 100644
> --- a/fs/ocfs2/super.c
> +++ b/fs/ocfs2/super.c
> @@ -1991,6 +1991,47 @@ static int ocfs2_setup_osb_uuid(struct ocfs2_super *osb, const unsigned char *uu
> return 0;
> }
>
> +/* Check to make sure entire volume is addressable on this system.
> + Requires osb_clusters_at_boot to be valid and for the journal to
> + have been read by jbd2_journal_load(). */
> +static int ocfs2_check_addressable(struct ocfs2_super *osb)
> +{
> + int status = 0;
> + u64 max_block =
> + ocfs2_clusters_to_blocks(osb->sb,
> + osb->osb_clusters_at_boot) - 1;
> +
> + /* Absolute addressability check (borrowed from ext4/super.c) */
> + if ((max_block >
> + (sector_t)(~0LL) >> (osb->sb->s_blocksize_bits - 9)) ||
> + (max_block > (pgoff_t)(~0LL) >> (PAGE_CACHE_SHIFT -
> + osb->sb->s_blocksize_bits))) {
> + mlog(ML_ERROR, "Volume too large "
> + "to mount safely on this system");
> + status = -EFBIG;
> + goto out;
> + }
> +
> + /* 32-bit block number is always OK. */
> + if (max_block <= (u32)~0UL)
> + goto out;
> +
> + /* Volume is "huge", so see if our journal is new enough to
> + support it. */
> + if (!(OCFS2_HAS_COMPAT_FEATURE(osb->sb,
> + OCFS2_FEATURE_COMPAT_JBD2_SB) &&
> + jbd2_journal_check_used_features(osb->journal->j_journal, 0, 0,
> + JBD2_FEATURE_INCOMPAT_64BIT))) {
> + mlog(ML_ERROR, "The journal cannot address the entire volume. "
> + "Enable the 'block64' journal option with tunefs.ocfs2");
> + status = -EFBIG;
> + goto out;
> + }
> +
> + out:
> + return status;
> +}
> +
> static int ocfs2_initialize_super(struct super_block *sb,
> struct buffer_head *bh,
> int sector_size,
> @@ -2215,14 +2256,6 @@ static int ocfs2_initialize_super(struct super_block *sb,
> goto bail;
> }
>
> - if (ocfs2_clusters_to_blocks(osb->sb, le32_to_cpu(di->i_clusters) - 1)
> - > (u32)~0UL) {
> - mlog(ML_ERROR, "Volume might try to write to blocks beyond "
> - "what jbd can address in 32 bits.\n");
> - status = -EINVAL;
> - goto bail;
> - }
> -
> if (ocfs2_setup_osb_uuid(osb, di->id2.i_super.s_uuid,
> sizeof(di->id2.i_super.s_uuid))) {
> mlog(ML_ERROR, "Out of memory trying to setup our uuid.\n");
> @@ -2404,6 +2437,12 @@ static int ocfs2_check_volume(struct ocfs2_super *osb)
> goto finally;
> }
>
> + /* Now that journal has been loaded, check to make sure entire
> + volume is addressable. */
> + status = ocfs2_check_addressable(osb);
> + if (status)
> + goto finally;
> +
> if (dirty) {
> /* recover my local alloc if we didn't unmount cleanly. */
> status = ocfs2_begin_local_alloc_recovery(osb,

This is completely unsafe. Two reasons. First, you're checking
the journal features after ocfs2_journal_load() has done recovery. This
may or may not be safe; recovering a 32bit journal probably works even
on a 64bit filesystem, and we shouldn't see that combination in the
wild anyway. That's not so bad.
Far worse is that you might recover a 64bit journal before
you've checked the sector_t or pagecache limits. That's not acceptable.
I think the best solution is to check all the limits before you
load the journal. However, jbd2 doesn't quite let you do that yet.
Thus, I propose the following jbd2 patch. jbd2 people, what do you
think:

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index bc2ff59..7922d87 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1365,6 +1365,8 @@ int jbd2_journal_check_used_features (journal_t
*journal,

if (!compat && !ro && !incompat)
return 1;
+ if (journal_get_superblock(journal))
+ return 0
if (journal->j_format_version == 1)
return 0;

If the jbd2 maintainers will allow this patch, you can put
together a two-change series that first modifies jbd2 and then adds
ocfs2_check_addressable() *before* ocfs2_journal_load().

Joel

--

Life's Little Instruction Book #314

"Never underestimate the power of forgiveness."

Joel Becker
Consulting Software Developer
Oracle
E-mail: joel.becker(a)oracle.com
Phone: (650) 506-8127
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