[PATCH v2] blk-cgroup: always terminate io.stat lines

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

With the removal of seq_get_buf in blkcg_print_one_stat, we
cannot make adding the newline conditional on there being
relevant stats because the name was already written out
unconditionally.
Otherwise we may end up with multiple device names in one
line which is confusing and doesn't follow the nested-keyed
file format.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Fixes: 252c651a4c85 ("blk-cgroup: stop using seq_get_buf")
---
Changes to v2:
* Address the warning about `has_stats` being unused now (sorry about
  that, built it as part of a package and missed that looked too trivial...)
* `pd_stat_fn` now returns `void`

Original v1 note:

I also switched to `seq_puts` as suggested by `checkpatch.pl`

This seemed like the simplest approach, so I thought I'd
send a patch.

On my physical machine, creating a new thin lv and starting
a container on it created lines such as

    253:10 253:5 rbytes=0 wbytes=0 rios=0 wios=1 dbytes=0 dios=0
    ^~~~~~ ^~~~~

This *looks* like the devices might just happen to have the
same stats, but that's not the case (and doesn't follow the
documented format).

With this patch this becomes:

    253:10
    253:5 rbytes=0 wbytes=0 rios=0 wios=1 dbytes=0 dios=0

Let me know if you prefer a different solution. I'm not sure
a temporary buffer that can be discarded would be much
better than the previous seq_get_buf() version. Otherwise
we'd need to change the `pd_stat_fn` interface to collect
the data separately and do the formatting afterwards I
suppose?

 block/blk-cgroup.c         | 9 ++-------
 block/blk-iocost.c         | 5 ++---
 block/blk-iolatency.c      | 6 ++----
 include/linux/blk-cgroup.h | 2 +-
 4 files changed, 7 insertions(+), 15 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 663aabfeba18..48e98c31a3d6 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -888,7 +888,6 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
 {
 	struct blkg_iostat_set *bis = &blkg->iostat;
 	u64 rbytes, wbytes, rios, wios, dbytes, dios;
-	bool has_stats = false;
 	const char *dname;
 	unsigned seq;
 	int i;
@@ -914,14 +913,12 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
 	} while (u64_stats_fetch_retry(&bis->sync, seq));
 
 	if (rbytes || wbytes || rios || wios) {
-		has_stats = true;
 		seq_printf(s, "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu",
 			rbytes, wbytes, rios, wios,
 			dbytes, dios);
 	}
 
 	if (blkcg_debug_stats && atomic_read(&blkg->use_delay)) {
-		has_stats = true;
 		seq_printf(s, " use_delay=%d delay_nsec=%llu",
 			atomic_read(&blkg->use_delay),
 			atomic64_read(&blkg->delay_nsec));
@@ -933,12 +930,10 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s)
 		if (!blkg->pd[i] || !pol->pd_stat_fn)
 			continue;
 
-		if (pol->pd_stat_fn(blkg->pd[i], s))
-			has_stats = true;
+		pol->pd_stat_fn(blkg->pd[i], s);
 	}
 
-	if (has_stats)
-		seq_printf(s, "\n");
+	seq_puts(s, "\n");
 }
 
 static int blkcg_print_stat(struct seq_file *sf, void *v)
diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 769b64394298..b4f1b7c1a965 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2995,13 +2995,13 @@ static void ioc_pd_free(struct blkg_policy_data *pd)
 	kfree(iocg);
 }
 
-static bool ioc_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
+static void ioc_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 {
 	struct ioc_gq *iocg = pd_to_iocg(pd);
 	struct ioc *ioc = iocg->ioc;
 
 	if (!ioc->enabled)
-		return false;
+		return;
 
 	if (iocg->level == 0) {
 		unsigned vp10k = DIV64_U64_ROUND_CLOSEST(
@@ -3017,7 +3017,6 @@ static bool ioc_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 			iocg->last_stat.wait_us,
 			iocg->last_stat.indebt_us,
 			iocg->last_stat.indelay_us);
-	return true;
 }
 
 static u64 ioc_weight_prfill(struct seq_file *sf, struct blkg_policy_data *pd,
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index 6593c7123b97..831e37b851c8 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -914,17 +914,16 @@ static bool iolatency_ssd_stat(struct iolatency_grp *iolat, struct seq_file *s)
 			(unsigned long long)stat.ps.missed,
 			(unsigned long long)stat.ps.total,
 			iolat->rq_depth.max_depth);
-	return true;
 }
 
-static bool iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
+static void iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 {
 	struct iolatency_grp *iolat = pd_to_lat(pd);
 	unsigned long long avg_lat;
 	unsigned long long cur_win;
 
 	if (!blkcg_debug_stats)
-		return false;
+		return;
 
 	if (iolat->ssd)
 		return iolatency_ssd_stat(iolat, s);
@@ -937,7 +936,6 @@ static bool iolatency_pd_stat(struct blkg_policy_data *pd, struct seq_file *s)
 	else
 		seq_printf(s, " depth=%u avg_lat=%llu win=%llu",
 			iolat->rq_depth.max_depth, avg_lat, cur_win);
-	return true;
 }
 
 static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp,
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index b4de2010fba5..132e05ed6935 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -152,7 +152,7 @@ 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 bool (blkcg_pol_stat_pd_fn)(struct blkg_policy_data *pd,
+typedef void (blkcg_pol_stat_pd_fn)(struct blkg_policy_data *pd,
 				struct seq_file *s);
 
 struct blkcg_policy {
-- 
2.30.2