[PATCH 09/49] blkcg: implement bio_associate_blkcg()

Tejun Heo
2015-04-06T19:59:51Z

Currently, a bio can only be associated with the io_context and blkcg
of %current using bio_associate_current(). This is too restrictive
for cgroup writeback support. Implement bio_associate_blkcg() which
associates a bio with the specified blkcg.

bio_associate_blkcg() leaves the io_context unassociated.
bio_associate_current() is updated so that it considers a bio as
already associated if it has a blkcg_css, instead of an io_context,
associated with it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Vivek Goyal <vgoyal@redhat.com>
---
block/bio.c | 24 +++++++++++++++++++++++-
include/linux/bio.h | 3 +++
2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 968683e..ab7517d 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1971,6 +1971,28 @@ struct bio_set *bioset_create_nobvec(unsigned int pool_size, unsigned int front_
EXPORT_SYMBOL(bioset_create_nobvec);

#ifdef CONFIG_BLK_CGROUP
+
+/**
+ * bio_associate_blkcg - associate a bio with the specified blkcg
+ * @bio: target bio
+ * @blkcg_css: css of the blkcg to associate
+ *
+ * Associate @bio with the blkcg specified by @blkcg_css. Block layer will
+ * treat @bio as if it were issued by a task which belongs to the blkcg.
+ *
+ * This function takes an extra reference of @blkcg_css which will be put
+ * when @bio is released. The caller must own @bio and is responsible for
+ * synchronizing calls to this function.
+ */
+int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css)
+{
+ if (unlikely(bio->bi_css))
+ return -EBUSY;
+ css_get(blkcg_css);
+ bio->bi_css = blkcg_css;
+ return 0;
+}
+
/**
* bio_associate_current - associate a bio with %current
* @bio: target bio
@@ -1988,7 +2010,7 @@ int bio_associate_current(struct bio *bio)
{
struct io_context *ioc;

- if (bio->bi_ioc)
+ if (bio->bi_css)
return -EBUSY;

ioc = current->io_context;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index da3a127..cbc5d1d 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -469,9 +469,12 @@ extern void bvec_free(mempool_t *, struct bio_vec *, unsigned int);
extern unsigned int bvec_nr_vecs(unsigned short idx);

#ifdef CONFIG_BLK_CGROUP
+int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css);
int bio_associate_current(struct bio *bio);
void bio_disassociate_task(struct bio *bio);
#else /* CONFIG_BLK_CGROUP */
+static inline int bio_associate_blkcg(struct bio *bio,
+ struct cgroup_subsys_state *blkcg_css) { return 0; }
static inline int bio_associate_current(struct bio *bio) { return -ENOENT; }
static inline void bio_disassociate_task(struct bio *bio) { }
#endif /* CONFIG_BLK_CGROUP */
--
2.1.0