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Subject[PATCH 03/13] blk-cgroup: allow controllers to output their own stats
Date
From: Josef Bacik <jbacik@fb.com>

blk-iolatency has a few stats that it would like to print out, and
instead of adding a bunch of crap to the generic code just provide a
helper so that controllers can add stuff to the stat line if they want
to.

Hide it behind a boot option since it changes the output of io.stat from
normal, and these stats are only interesting to developers.

Signed-off-by: Josef Bacik <jbacik@fb.com>
---
block/blk-cgroup.c | 61 +++++++++++++++++++++++++++++++++++++++++++---
include/linux/blk-cgroup.h | 3 +++
2 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index eb85cb87c40f..b2ac6a7f851f 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -50,6 +50,8 @@ static struct blkcg_policy *blkcg_policy[BLKCG_MAX_POLS];

static LIST_HEAD(all_blkcgs); /* protected by blkcg_pol_mutex */

+static bool blkcg_debug_stats = false;
+
static bool blkcg_policy_enabled(struct request_queue *q,
const struct blkcg_policy *pol)
{
@@ -954,13 +956,28 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)

hlist_for_each_entry_rcu(blkg, &blkcg->blkg_list, blkcg_node) {
const char *dname;
+ char *buf;
struct blkg_rwstat rwstat;
u64 rbytes, wbytes, rios, wios;
+ size_t size = seq_get_buf(sf, &buf), count = 0, total = 0;
+ int i;

dname = blkg_dev_name(blkg);
if (!dname)
continue;

+ /*
+ * Hooray string manipulation, count is the size written NOT
+ * INCLUDING THE \0, so size is now count+1 less than what we
+ * had before, but we want to start writing the next bit from
+ * the \0 so we only add count to buf.
+ */
+ count = snprintf(buf, size, "%s ", dname);
+ if (count >= size)
+ continue;
+ buf += count;
+ size -= count + 1;
+
spin_lock_irq(blkg->q->queue_lock);

rwstat = blkg_rwstat_recursive_sum(blkg, NULL,
@@ -975,9 +992,44 @@ static int blkcg_print_stat(struct seq_file *sf, void *v)

spin_unlock_irq(blkg->q->queue_lock);

- if (rbytes || wbytes || rios || wios)
- seq_printf(sf, "%s rbytes=%llu wbytes=%llu rios=%llu wios=%llu\n",
- dname, rbytes, wbytes, rios, wios);
+ if (rbytes || wbytes || rios || wios) {
+ total += count;
+ count = snprintf(buf, size,
+ "rbytes=%llu wbytes=%llu rios=%llu wios=%llu",
+ rbytes, wbytes, rios, wios);
+ if (count >= size)
+ continue;
+ buf += count;
+ total += count;
+ size -= count + 1;
+ }
+
+ if (!blkcg_debug_stats)
+ goto next;
+
+ mutex_lock(&blkcg_pol_mutex);
+ for (i = 0; i < BLKCG_MAX_POLS; i++) {
+ struct blkcg_policy *pol = blkcg_policy[i];
+
+ if (!blkg->pd[i] || !pol->pd_stat_fn)
+ continue;
+
+ count = pol->pd_stat_fn(blkg->pd[i], buf, size);
+ if (count >= size)
+ continue;
+ buf += count;
+ total += count;
+ size -= count + 1;
+ }
+ mutex_unlock(&blkcg_pol_mutex);
+next:
+ if (total) {
+ count = snprintf(buf, size, "\n");
+ if (count >= size)
+ continue;
+ total += count;
+ seq_commit(sf, total);
+ }
}

rcu_read_unlock();
@@ -1547,3 +1599,6 @@ void blkcg_policy_unregister(struct blkcg_policy *pol)
mutex_unlock(&blkcg_pol_register_mutex);
}
EXPORT_SYMBOL_GPL(blkcg_policy_unregister);
+
+module_param(blkcg_debug_stats, bool, 0444);
+MODULE_PARM_DESC(blkcg_debug_stats, "True if you want debug stats, false if not");
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 69aa71dc0c04..b41292726c0f 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -148,6 +148,8 @@ typedef void (blkcg_pol_online_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_offline_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_free_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkg_policy_data *pd);
+typedef size_t (blkcg_pol_stat_pd_fn)(struct blkg_policy_data *pd, char *buf,
+ size_t size);

struct blkcg_policy {
int plid;
@@ -167,6 +169,7 @@ struct blkcg_policy {
blkcg_pol_offline_pd_fn *pd_offline_fn;
blkcg_pol_free_pd_fn *pd_free_fn;
blkcg_pol_reset_pd_stats_fn *pd_reset_stats_fn;
+ blkcg_pol_stat_pd_fn *pd_stat_fn;
};

extern struct blkcg blkcg_root;
--
2.14.3
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