[PATCH v2 6/7] bio: add a helper calculating nr segments to alloc

Pavel Begunkov
2021-01-02T15:23:42Z

Add a helper function calculating the number of bvec segments we need to
allocate to construct a bio. It doesn't change anything functionally,
but will be used to not duplicate special cases in the future.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
fs/block_dev.c | 7 ++++---
fs/iomap/direct-io.c | 9 ++++-----
include/linux/bio.h | 10 ++++++++++
3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 3e5b02f6606c..034e6c8cfcab 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -416,7 +416,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
dio->size += bio->bi_iter.bi_size;
pos += bio->bi_iter.bi_size;

- nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
+ nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_PAGES);
if (!nr_pages) {
bool polled = false;

@@ -481,9 +481,10 @@ blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
{
int nr_pages;

- nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES + 1);
- if (!nr_pages)
+ if (!iov_iter_count(iter))
return 0;
+
+ nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_PAGES + 1);
if (is_sync_kiocb(iocb) && nr_pages <= BIO_MAX_PAGES)
return __blkdev_direct_IO_simple(iocb, iter, nr_pages);

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 933f234d5bec..ea1e8f696076 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -250,11 +250,8 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
orig_count = iov_iter_count(dio->submit.iter);
iov_iter_truncate(dio->submit.iter, length);

- nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
- if (nr_pages <= 0) {
- ret = nr_pages;
+ if (!iov_iter_count(dio->submit.iter))
goto out;
- }

if (need_zeroout) {
/* zero out from the start of the block to the write offset */
@@ -263,6 +260,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
iomap_dio_zero(dio, iomap, pos - pad, pad);
}

+ nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_PAGES);
do {
size_t n;
if (dio->error) {
@@ -308,7 +306,8 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
dio->size += n;
copied += n;

- nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
+ nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
+ BIO_MAX_PAGES);
iomap_dio_submit_bio(dio, iomap, bio, pos);
pos += n;
} while (nr_pages);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 1edda614f7ce..d8f9077c43ef 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -10,6 +10,7 @@
#include <linux/ioprio.h>
/* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
#include <linux/blk_types.h>
+#include <linux/uio.h>

#define BIO_DEBUG

@@ -441,6 +442,15 @@ static inline void bio_wouldblock_error(struct bio *bio)
bio_endio(bio);
}

+/*
+ * Calculate number of bvec segments that should be allocated to fit data
+ * pointed by @iter.
+ */
+static inline int bio_iov_vecs_to_alloc(struct iov_iter *iter, int max_segs)
+{
+ return iov_iter_npages(iter, max_segs);
+}
+
struct request_queue;

extern int submit_bio_wait(struct bio *bio);
--
2.24.0