ocfs2: add errors=continue

OCFS2 is often used in high-availaibility systems.  However, ocfs2
converts the filesystem to read-only at the drop of the hat.  This may
not be necessary, since turning the filesystem read-only would affect
other running processes as well, decreasing availability.

This attempt is to add errors=continue, which would return the EIO to
the calling process and terminate furhter processing so that the
filesystem is not corrupted further.  However, the filesystem is not
converted to read-only.

As a future plan, I intend to create a small utility or extend
fsck.ocfs2 to fix small errors such as in the inode.  The input to the
utility such as the inode can come from the kernel logs so we don't have
to schedule a downtime for fixing small-enough errors.

The patch changes the ocfs2_error to return an error.  The error
returned depends on the mount option set.  If none is set, the default
is to turn the filesystem read-only.

Perhaps errors=continue is not the best option name.  Historically it is
used for making an attempt to progress in the current process itself.
Should we call it errors=eio? or errors=killproc? Suggestions/Comments
welcome.

Sources are available at:
  https://github.com/goldwynr/linux/tree/error-cont



Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>