[RFC 01/16] blkcg:Introduce blkio.app_identifier knob to blkio controller

[Muneendra <muneendra.kumar@broadcom.com>]

This Patch added a unique application identifier i.e
blkio.app_identifier knob to  blkio controller which
allows identification of traffic sources at an
individual cgroup based Applications
(ex:virtual machine (VM))level in both host and
fabric infrastructure.

Also provided an interface blkcg_get_app_identifier to
grab the app identifier associated with a bio.

Added a sysfs interface blkio.app_identifier to get/set the appid.

This capability can be utilized by multiple block transport infrastructure
like fc,iscsi,roce ..

Signed-off-by: Muneendra <muneendra.kumar@broadcom.com>
---
 block/blk-cgroup.c         | 32 ++++++++++++++++++++++++++++++++
 include/linux/blk-cgroup.h | 19 +++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 0ecc897b225c..697eccb3ba7a 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -492,6 +492,33 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css,
 	return 0;
 }
 
+static int blkcg_read_appid(struct seq_file *sf, void *v)
+{
+	struct blkcg *blkcg = css_to_blkcg(seq_css(sf));
+
+	seq_printf(sf, "%s\n", blkcg->app_identifier);
+	return 0;
+}
+
+static ssize_t blkcg_write_appid(struct kernfs_open_file *of,
+					 char *buf, size_t nbytes, loff_t off)
+{
+	struct cgroup_subsys_state *css = of_css(of);
+	struct blkcg *blkcg = css_to_blkcg(css);
+	struct blkcg_gq *blkg;
+	int i;
+
+	buf = strstrip(buf);
+	if (blkcg) {
+		if (nbytes < APPID_LEN)
+			strlcpy(blkcg->app_identifier, buf, nbytes);
+		else
+			return -EINVAL;
+	}
+	return nbytes;
+}
+
+
 const char *blkg_dev_name(struct blkcg_gq *blkg)
 {
 	/* some drivers (floppy) instantiate a queue w/o disk registered */
@@ -844,6 +871,11 @@ static struct cftype blkcg_legacy_files[] = {
 		.name = "reset_stats",
 		.write_u64 = blkcg_reset_stats,
 	},
+	{
+		.name = "app_identifier",
+		.write = blkcg_write_appid,
+		.seq_show = blkcg_read_appid,
+	},
 	{ }	/* terminate */
 };
 
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index a57ebe2f00ab..3676d7ebb19f 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -30,6 +30,7 @@
 
 /* Max limits for throttle policy */
 #define THROTL_IOPS_MAX		UINT_MAX
+#define APPID_LEN		128
 
 #ifdef CONFIG_BLK_CGROUP
 
@@ -55,6 +56,7 @@ struct blkcg {
 	struct blkcg_policy_data	*cpd[BLKCG_MAX_POLS];
 
 	struct list_head		all_blkcgs_node;
+	char				app_identifier[APPID_LEN];
 #ifdef CONFIG_CGROUP_WRITEBACK
 	struct list_head		cgwb_list;
 #endif
@@ -239,6 +241,23 @@ static inline struct blkcg *css_to_blkcg(struct cgroup_subsys_state *css)
 	return css ? container_of(css, struct blkcg, css) : NULL;
 }
 
+/**
+ * blkcg_get_app_identifier - grab the app identifier associated with a bio
+ * @bio: target bio
+ *
+ * This returns the app identifier associated with a bio,
+ * %NULL if not associated.
+ * Callers are expected to either handle %NULL or know association has been
+ * done prior to calling this.
+ */
+static inline char *blkcg_get_app_identifier(struct bio *bio)
+{
+	if (bio && (bio->bi_blkg) &&
+			(strlen(bio->bi_blkg->blkcg->app_identifier)))
+		return bio->bi_blkg->blkcg->app_identifier;
+	return NULL;
+}
+
 /**
  * __bio_blkcg - internal, inconsistent version to get blkcg
  *
-- 
2.18.2