ocfs2: Add metadata ECC - almost there.

These patches add the metadata ECC code to ocfs2. They have one limitation - they do not ECC directory blocks yet. However, that will only take a simple insertion of the dirblock trailer. With xattr ECC completed, the patches are approaching a final form and are ready for initial review. They are atop my xattr-buckets-2 branch.

The first patch adds buffer triggers to JDB2. This allows us to only calculate the ECC code when JBD2 is about to write a block to disk.

Next, we add the actual blockcheck functions. These are the functions that compute the checksum (using the kernel's crc32_le()) and the ECC bits (this is hamming code, implemented in blockcheck.c).

Then we create metadata-type specific ocfs2_journal_access_*() functions to make sure each metadata type uses its own checksum field. These are hooked up to the regular metadata types.

We add ecc calculation to xattr buckets. Because buckets can be multiple blocks, they cannot use journal triggers. However, they are rarely updated, so the loss of efficiency isn't very important.

Last, we refactor the xattr value setting code to make sure we know which metadata type an xattr value belongs to. That way we can call the appropriate ocfs2_journal_access_*() function.

The code is also available in my repository.

[View]
http://oss.oracle.com/git/?p=jlbec/linux-2.6.git;a=shortlog;h=metaecc
[Pull]
git://oss.oracle.com/git/jlbec/linux-2.6.git metaecc

Joel Becker (18):
jbd2: Add buffer triggers
ocfs2: Add the on-disk structures for metadata checksums.
ocfs2: Add the underlying blockcheck code.
ocfs2: Add a validation hook for quota block reads.
ocfs2: block read meta ecc.
ocfs2: Add journal_access functions with jbd2 triggers.
ocfs2: Wrap up the common use cases of ocfs2_new_path().
ocfs2: Use metadata-specific ocfs2_journal_access_*() functions.
ocfs2: Add ecc and checksums to ocfs2 xattr buckets.
ocfs2: Create ocfs2_xattr_value_buf.

ocfs2: Pull ocfs2_xattr_value_buf up from __ocfs2_remove_xattr_range().
ocfs2: Pull ocfs2_xattr_value_buf up into ocfs2_xattr_value_truncate().
ocfs2: Pass ocfs2_xattr_value_buf into ocfs2_xattr_value_truncate().
ocfs2: Pass value buf to ocfs2_xattr_update_entry().
ocfs2: Use ocfs2_xattr_value_buf in ocfs2_xattr_set_entry().
ocfs2: Pass value buf to ocfs2_remove_value_outside().
ocfs2: Use proper journal_access function in xattr.c
ocfs2: Enable metadata checksums.