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SubjectRe: [PATCH v3 07/49] bcache: comment on direct access to bvec table
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On 2017/8/8 下午4:45, Ming Lei wrote:
> Looks all are safe after multipage bvec is supported.
>
> Cc: linux-bcache@vger.kernel.org
> Signed-off-by: Ming Lei <ming.lei@redhat.com>

Acked-by: Coly Li <colyli@suse.de>

Coly Li


> ---
> drivers/md/bcache/btree.c | 1 +
> drivers/md/bcache/super.c | 6 ++++++
> drivers/md/bcache/util.c | 7 +++++++
> 3 files changed, 14 insertions(+)
>
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index 866dcf78ff8e..3da595ae565b 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -431,6 +431,7 @@ static void do_btree_node_write(struct btree *b)
>
> continue_at(cl, btree_node_write_done, NULL);
> } else {
> + /* No harm for multipage bvec since the new is just allocated */
> b->bio->bi_vcnt = 0;
> bch_bio_map(b->bio, i);
>
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 8352fad765f6..6808f548cd13 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -208,6 +208,7 @@ static void write_bdev_super_endio(struct bio *bio)
>
> static void __write_super(struct cache_sb *sb, struct bio *bio)
> {
> + /* single page bio, safe for multipage bvec */
> struct cache_sb *out = page_address(bio->bi_io_vec[0].bv_page);
> unsigned i;
>
> @@ -1154,6 +1155,8 @@ static void register_bdev(struct cache_sb *sb, struct page *sb_page,
> dc->bdev->bd_holder = dc;
>
> bio_init(&dc->sb_bio, dc->sb_bio.bi_inline_vecs, 1);
> +
> + /* single page bio, safe for multipage bvec */
> dc->sb_bio.bi_io_vec[0].bv_page = sb_page;
> get_page(sb_page);
>
> @@ -1799,6 +1802,7 @@ void bch_cache_release(struct kobject *kobj)
> for (i = 0; i < RESERVE_NR; i++)
> free_fifo(&ca->free[i]);
>
> + /* single page bio, safe for multipage bvec */
> if (ca->sb_bio.bi_inline_vecs[0].bv_page)
> put_page(ca->sb_bio.bi_io_vec[0].bv_page);
>
> @@ -1854,6 +1858,8 @@ static int register_cache(struct cache_sb *sb, struct page *sb_page,
> ca->bdev->bd_holder = ca;
>
> bio_init(&ca->sb_bio, ca->sb_bio.bi_inline_vecs, 1);
> +
> + /* single page bio, safe for multipage bvec */
> ca->sb_bio.bi_io_vec[0].bv_page = sb_page;
> get_page(sb_page);
>
> diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c
> index 8c3a938f4bf0..11b4230ea6ad 100644
> --- a/drivers/md/bcache/util.c
> +++ b/drivers/md/bcache/util.c
> @@ -223,6 +223,13 @@ uint64_t bch_next_delay(struct bch_ratelimit *d, uint64_t done)
> : 0;
> }
>
> +/*
> + * Generally it isn't good to access .bi_io_vec and .bi_vcnt
> + * directly, the preferred way is bio_add_page, but in
> + * this case, bch_bio_map() supposes that the bvec table
> + * is empty, so it is safe to access .bi_vcnt & .bi_io_vec
> + * in this way even after multipage bvec is supported.
> + */
> void bch_bio_map(struct bio *bio, void *base)
> {
> size_t size = bio->bi_iter.bi_size;
>

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