[PATCH v2 2/7] bvec/iter: disallow zero-length segment bvecs

Pavel Begunkov
2021-01-02T15:22:41Z

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.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
Documentation/filesystems/porting.rst | 7 +++++++
lib/iov_iter.c | 2 --
2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index 867036aa90b8..c722d94f29ea 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -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.
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 1635111c5bd2..7de304269641 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -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); \
} \
}
--
2.24.0