[Devel] [PATCH 1/3] blkcg: implement bio_associate_blkcg()

[Andrei Vagin]

From: Tejun Heo <tj at kernel.org>

ML: 1d933cf096e3aea15f1aec8297657b7a846fab63

Currently, a bio can only be associated with the io_context and
g
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 at kernel.org>
Cc: Jens Axboe <axboe at kernel.dk>
Cc: Vivek Goyal <vgoyal at redhat.com>
Signed-off-by: Jens Axboe <axboe at fb.com>
Signed-off-by: Andrei Vagin <avagin at openvz.org>
---
 fs/bio.c            | 25 ++++++++++++++++++++++++-
 include/linux/bio.h |  3 +++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/fs/bio.c b/fs/bio.c
index bfa6cdc..b9b6a2c 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -2126,6 +2126,29 @@ bad:
 EXPORT_SYMBOL(bioset_create);
 
 #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;
+}
+EXPORT_SYMBOL(bio_associate_blkcg);
+
 /**
  * bio_associate_current - associate a bio with %current
  * @bio: target bio
@@ -2144,7 +2167,7 @@ int bio_associate_current(struct bio *bio)
 	struct io_context *ioc;
 	struct cgroup_subsys_state *css;
 
-	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 34be583..877f8de 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -319,9 +319,12 @@ 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 */
-- 
1.8.3.1