diff options
author | Jens Axboe <axboe@kernel.dk> | 2019-02-27 23:05:25 +0300 |
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committer | Jens Axboe <axboe@kernel.dk> | 2019-03-18 19:44:48 +0300 |
commit | 875f1d0769cdcfe1596ff0ca609b453359e42ec9 (patch) | |
tree | 7a62a8236e2412bc136376e0c22114b5e631f98a /include/linux/uio.h | |
parent | bf33a7699e992b12d4c7d39dc3f0b61f6b26c5c2 (diff) | |
download | linux-875f1d0769cdcfe1596ff0ca609b453359e42ec9.tar.xz |
iov_iter: add ITER_BVEC_FLAG_NO_REF flag
For ITER_BVEC, if we're holding on to kernel pages, the caller
doesn't need to grab a reference to the bvec pages, and drop that
same reference on IO completion. This is essentially safe for any
ITER_BVEC, but some use cases end up reusing pages and uncondtionally
dropping a page reference on completion. And example of that is
sendfile(2), that ends up being a splice_in + splice_out on the
pipe pages.
Add a flag that tells us it's fine to not grab a page reference
to the bvec pages, since that caller knows not to drop a reference
when it's done with the pages.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/linux/uio.h')
-rw-r--r-- | include/linux/uio.h | 24 |
1 files changed, 19 insertions, 5 deletions
diff --git a/include/linux/uio.h b/include/linux/uio.h index ecf584f6b82d..4e926641fa80 100644 --- a/include/linux/uio.h +++ b/include/linux/uio.h @@ -23,14 +23,23 @@ struct kvec { }; enum iter_type { - ITER_IOVEC = 0, - ITER_KVEC = 2, - ITER_BVEC = 4, - ITER_PIPE = 8, - ITER_DISCARD = 16, + /* set if ITER_BVEC doesn't hold a bv_page ref */ + ITER_BVEC_FLAG_NO_REF = 2, + + /* iter types */ + ITER_IOVEC = 4, + ITER_KVEC = 8, + ITER_BVEC = 16, + ITER_PIPE = 32, + ITER_DISCARD = 64, }; struct iov_iter { + /* + * Bit 0 is the read/write bit, set if we're writing. + * Bit 1 is the BVEC_FLAG_NO_REF bit, set if type is a bvec and + * the caller isn't expecting to drop a page reference when done. + */ unsigned int type; size_t iov_offset; size_t count; @@ -84,6 +93,11 @@ static inline unsigned char iov_iter_rw(const struct iov_iter *i) return i->type & (READ | WRITE); } +static inline bool iov_iter_bvec_no_ref(const struct iov_iter *i) +{ + return (i->type & ITER_BVEC_FLAG_NO_REF) != 0; +} + /* * Total number of bytes covered by an iovec. * |