[RFC v2 02/18] blkcg: Added a app identifier support for blkcg

[Muneendra <muneendra.kumar@xxxxxxxxxxxx>]

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

Provided the interface blkcg_get_app_identifier to
grab the app identifier associated with a bio.

Provided the interface blkcg_set_app_identifier to
set the app identifier in a blkcgrp associated with cgroup id

Signed-off-by: Muneendra <muneendra.kumar@xxxxxxxxxxxx>

---
v2:
renamed app_identifier to app_id
removed the  sysfs interface blkio.app_identifie under
/sys/fs/cgroup/blkio
Added a new interface blkcg_set_app_identifier
---
 block/blk-cgroup.c         | 31 +++++++++++++++++++++++++++++++
 include/linux/blk-cgroup.h | 22 ++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 619a79b51068..672971521010 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -546,6 +546,37 @@ static struct blkcg_gq *blkg_lookup_check(struct blkcg *blkcg,
 	return __blkg_lookup(blkcg, q, true /* update_hint */);
 }
 
+/*
+ * Sets the app_identifier field associted to blkcg
+ * @buf: application identifier
+ * @id: cgrp id
+ * @len: size of appid
+ */
+int blkcg_set_app_identifier(char *buf, u64 id, size_t len)
+{
+	struct cgroup *cgrp = NULL;
+	struct cgroup_subsys_state *css = NULL;
+	struct blkcg *blkcg = NULL;
+
+	cgrp = cgroup_get_from_kernfs_id(id);
+	if (!cgrp)
+		return -ENOENT;
+
+	css = cgroup_get_e_css(cgrp, &io_cgrp_subsys);
+	if (!css)
+		return -ENOENT;
+
+	blkcg = css_to_blkcg(css);
+	if (!blkcg)
+		return -ENOENT;
+
+	if (len > APPID_LEN)
+		return -EINVAL;
+	strlcpy(blkcg->app_id, buf, len);
+	return 0;
+}
+EXPORT_SYMBOL(blkcg_set_app_identifier);
+
 /**
  * blkg_conf_prep - parse and prepare for per-blkg config update
  * @inputp: input string pointer
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index c8fc9792ac77..5bd3f9f397ac 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -30,6 +30,8 @@
 
 /* Max limits for throttle policy */
 #define THROTL_IOPS_MAX		UINT_MAX
+#define APPID_LEN              128
+
 
 #ifdef CONFIG_BLK_CGROUP
 
@@ -55,6 +57,8 @@ struct blkcg {
 	struct blkcg_policy_data	*cpd[BLKCG_MAX_POLS];
 
 	struct list_head		all_blkcgs_node;
+	char                            app_id[APPID_LEN];
+
 #ifdef CONFIG_CGROUP_WRITEBACK
 	struct list_head		cgwb_list;
 #endif
@@ -206,6 +210,24 @@ struct gendisk *blkcg_conf_get_disk(char **inputp);
 int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 		   char *input, struct blkg_conf_ctx *ctx);
 void blkg_conf_finish(struct blkg_conf_ctx *ctx);
+int blkcg_set_app_identifier(char *buf, u64 id, size_t len);
+
+/**
+ * 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_id))
+		return bio->bi_blkg->blkcg->app_id;
+	return NULL;
+}
 
 /**
  * blkcg_css - find the current css
-- 
2.26.2

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