On Thu, Feb 24, 2011 at 12:37:53PM -0500, Chris Mason wrote: > Excerpts from Jan Kara's message of 2011-02-24 11:47:58 -0500: > > On Wed 23-02-11 15:35:11, Chris Mason wrote: > > > Excerpts from Joel Becker's message of 2011-02-23 15:24:47 -0500: > > > > On Tue, Feb 22, 2011 at 11:45:44AM -0500, Martin K. Petersen wrote: > > > > > Also, DIX is only the tip of the iceberg. Many other impending > > > > > technologies feature checksums and require pages to be stable during I/O > > > > > due to checksumming, encryption and so on. > > > > > > > > > > The VM is already trying to do the right thing. We just need the > > > > > relevant filesystems to catch up. > > > > > > > > ocfs2 handles stable metadata for its checksums when feeding > > > > things to the journal. If we're doing pagecache-based I/O, is the > > > > pagecache going to help here for data? > > > > > > Data is much easier than metadata. All you really need is to wait on > > > writeback in file_write, wait on writeback in page_mkwrite, and make > > > sure you don't free blocks back to the allocator that are actively under > > > IO. > > > > > > I expect the hard part to be jbd and metadata in ext34. > > But JBD already has to do data copy if a buffer is going to be modified > > before/while it is written to the journal. So we should alredy do all that > > is needed for metadata. I don't say there aren't any bugs as they could be > > triggered only by crashing at the wrong moment and observing fs corruption. > > But most of the work should be there... > > Most of it is there, but there are always little bits and pieces. The > ext4 journal csumming code was one semi-recent example where we found > metadata changing in flight. > > A big part of testing this is getting some way to detect the bugs > without dif/dix. With btrfs I have patches to do set_memory_ro on > pages once I've don the crc, hopefully we can generalize that idea or > some up with something smarter. Right now I'm faking it with modprobe scsi_debug ato=1 guard=1 dif=3 dix=199. Hm, would you mind sharing those patches? I've been working on a second patch to do the wait-on-writeback per everyone's suggestions, but I still see the occasional corruption error as soon as I enable the mmap write case and covet some more debugging tools. It does seem to be working for the pure pwrite() case. :) --D -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
