On Tue 24-01-12 19:21:19, Dave Chinner wrote:

On Fri, Jan 20, 2012 at 09:34:40PM +0100, Jan Kara wrote:

quoted

There are three entry points which dirty pages in a filesystem.  mmap (handled
by block_page_mkwrite()), buffered write (handled by
__generic_file_aio_write()), and truncate (it can dirty last partial page -
handled inside each filesystem separately). Protect these places with
sb_start_write() and sb_end_write().

fallocate can also dirty pages, either during preallocation or hole
punching.  Hence if you are going to promote truncate to
SB_FREEZE_WRITE protection then you need to promote everything else
that can zero partial blocks as well.

That also means that anything the has implemented XFS_IOC_ ioctl
interfaces for prellocation and hole punching (xfs, ocfs2 and gfs2
IIRC) also needs to be protected in the same way.

  Yeah, you are right. As I wrote in the introductory mail, there's problem
with metadata operations (e.g. directory modifications) anyway so we'll
have to audit all places where transactions are started. First I'll do this
for ext4 as a POC and then I'll try to do that for XFS if Eric doesn't beat
me to it (he promised to have a look at XFS part ;).

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR

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