On Mon, Mar 01, 2010 at 03:21:49PM -0800, Andrew Morton wrote: > On Thu, 25 Feb 2010 15:45:58 +0300 > Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote: > > > Can someone please describe me why directio deny partial writes. > > For example if someone try to write 100Mb but file system has less > > data it return ENOSPC in the middle of block allocation. > > All allocated blocks will be truncated (it may be 100Mb -4k) end > > ENOSPC will be returned. As far as i remember direct_io always act > > like this, but i never asked why? > > Why do we have to give up all the progress we made? > > In fact partial writes are possible in case of holes, when we > > fall back to buffered write. XFS implemented partial writes. > > The problem with direct-io writes is that the writes don't necessarily > complete in file-offset-ascending order. So if we've issued 50 write > BIOs and then hit an EIO on a BIO then we could have a hunk of > unwritten data with newly-writted data either side of it. If we get a > bunch of discontiguous EIO BIOs coming in then the problem gets even > messier - we have a span of disk which has a random mix of > correctly-written and not-correctly-written runs of sectors. What do > we do with that? Hmm, what if we're filling in a hole with direct IO? I don't see where blocks allocated in DIO code will be trimmed on a failed write (because it's within isize). This could cause uninitalized data of the block to leak couldn't it? -- 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
