Commit 9b2e0016 authored by Pavel Begunkov's avatar Pavel Begunkov Committed by Jens Axboe
Browse files

bvec/iter: disallow zero-length segment bvecs 



zero-length bvec segments are allowed in general, but not handled by bio
and down the block layer so filtered out. This inconsistency may be
confusing and prevent from optimisations. As zero-length segments are
useless and places that were generating them are patched, declare them
not allowed.

Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarPavel Begunkov <asml.silence@gmail.com>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 0f1d344f

Documentation/block/biovecs.rst

+2 −0
Original line number Diff line number Diff line
@@ -40,6 +40,8 @@ normal code doesn't have to deal with bi_bvec_done. 
   There is a lower level advance function - bvec_iter_advance() - which takes

   a pointer to a biovec, not a bio; this is used by the bio integrity code.



As of 5.12 bvec segments with zero bv_len are not supported.



What's all this get us?

=======================

Documentation/filesystems/porting.rst

+7 −0
Original line number Diff line number Diff line
@@ -865,3 +865,10 @@ no matter what. Everything is handled by the caller. 


clone_private_mount() returns a longterm mount now, so the proper destructor of

its result is kern_unmount() or kern_unmount_array().



---



**mandatory**



zero-length bvec segments are disallowed, they must be filtered out before

passed on to an iterator.

lib/iov_iter.c

+0 −2
Original line number Diff line number Diff line
@@ -72,8 +72,6 @@ 
	__start.bi_bvec_done = skip;			\

	__start.bi_idx = 0;				\

	for_each_bvec(__v, i->bvec, __bi, __start) {	\

		if (!__v.bv_len)			\

			continue;			\

		(void)(STEP);				\

	}						\

}