Hello, Kent. On Fri, Aug 24, 2012 at 12:05:08AM -0700, Kent Overstreet wrote: > > I'm pretty sure I sound like a broken record by now, but > > > > * How was this tested? > > > > * What are the implications and possible dangers? > > I've said all that on list, but I gather what you really wanted was to > have it all in the patch description. Will do. Yeap. > > > @@ -463,10 +468,10 @@ void __bio_clone(struct bio *bio, struct bio *bio_src) > > > bio->bi_sector = bio_src->bi_sector; > > > bio->bi_bdev = bio_src->bi_bdev; > > > bio->bi_flags |= 1 << BIO_CLONED; > > > + bio->bi_flags &= ~(1 << BIO_SEG_VALID); > > > > For the n'th time, explain please. > > Argh, I could've sworn I dropped that part. Can we drop it tho? If we're changing bvecs, we probably should be clearing SEG_VALID on both bios. > commit 0edda563aef9432b45f0c6a50f52590b92594560 > Author: Kent Overstreet <koverstreet@xxxxxxxxxx> > Date: Thu Aug 23 23:26:38 2012 -0700 > > block: Only clone bio vecs that are in use > > bcache creates large bios internally, and then splits them according to > the device requirements before it sends them down. If a lower level > device tries to clone the bio, and the original bio had more than > BIO_MAX_PAGES, the clone will fail unecessarily. > > We can fix this by only cloning the bio vecs that are actually in use - > as for as the block layer is concerned the new bio is still equivalent > to the old bio. > > This code should in general be safe as long as all the block layer code > uses bi_idx, bi_vcnt consistently; since bios are cloned by code that > doesn't own the original bio there's little room for issues caused by > code playing games with the original bio's bi_io_vec. One perhaps > imagine code depending the clone and original bio's io vecs lining up a > certain way, but auditing and testing haven't turned up anything. > > Testing: This code has been in the bcache tree for quite awhile, and has > been tested with various md layers and dm targets (including strange > things like multipath). Yeap, looks much better to me. Thanks. -- tejun -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
