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authorJens Axboe <axboe@kernel.dk>2019-02-27 13:05:25 -0700
committerJens Axboe <axboe@kernel.dk>2019-03-18 10:44:48 -0600
commit875f1d0769cdcfe1596ff0ca609b453359e42ec9 (patch)
tree7a62a8236e2412bc136376e0c22114b5e631f98a /include/linux/uio.h
parentbf33a7699e992b12d4c7d39dc3f0b61f6b26c5c2 (diff)
downloadlinux-875f1d0769cdcfe1596ff0ca609b453359e42ec9.tar.gz
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.h24
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.
*