block: include empty disks in /proc/diskstats

/proc/diskstats used to show stats for all disks whether they're
zero-sized or not and their non-zero partitions.  Commit
074a7aca7afa6f230104e8e65eba3420263714a5 accidentally changed the
behavior such that it doesn't print out zero sized disks.  This patch
implements DISK_PITER_INCL_EMPTY_PART0 flag to partition iterator and
uses it in diskstats_show() such that empty part0 is shown in
/proc/diskstats.

Reported and bisectd by Dianel Collins.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Daniel Collins <solemnwarning@solemnwarning.no-ip.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

2 files changed, 9 insertions, 4 deletions

diff --git a/block/genhd.c b/block/genhd.c
index a9ec910974c1..1a4916e01732 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -98,7 +98,7 @@ void disk_part_iter_init(struct disk_part_iter *piter, struct gendisk *disk,
 
         if (flags & DISK_PITER_REVERSE)
                 piter->idx = ptbl->len - 1;
-        else if (flags & DISK_PITER_INCL_PART0)
+        else if (flags & (DISK_PITER_INCL_PART0 | DISK_PITER_INCL_EMPTY_PART0))
                 piter->idx = 0;
         else
                 piter->idx = 1;
@@ -134,7 +134,8 @@ struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter)
         /* determine iteration parameters */
         if (piter->flags & DISK_PITER_REVERSE) {
                 inc = -1;
-                if (piter->flags & DISK_PITER_INCL_PART0)
+                if (piter->flags & (DISK_PITER_INCL_PART0 |
+                                    DISK_PITER_INCL_EMPTY_PART0))
                         end = -1;
                 else
                         end = 0;
@@ -150,7 +151,10 @@ struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter)
                 part = rcu_dereference(ptbl->part[piter->idx]);
                 if (!part)
                         continue;
-                if (!(piter->flags & DISK_PITER_INCL_EMPTY) && !part->nr_sects)
+                if (!part->nr_sects &&
+                    !(piter->flags & DISK_PITER_INCL_EMPTY) &&
+                    !(piter->flags & DISK_PITER_INCL_EMPTY_PART0 &&
+                      piter->idx == 0))
                         continue;
 
                 get_device(part_to_dev(part));
@@ -1011,7 +1015,7 @@ static int diskstats_show(struct seq_file *seqf, void *v)
                                 "\n\n");
         */
  
-        disk_part_iter_init(&piter, gp, DISK_PITER_INCL_PART0);
+        disk_part_iter_init(&piter, gp, DISK_PITER_INCL_EMPTY_PART0);
         while ((hd = disk_part_iter_next(&piter))) {
                 cpu = part_stat_lock();
                 part_round_stats(cpu, hd);
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 634c53028fb8..a1a28caed23d 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -214,6 +214,7 @@ static inline void disk_put_part(struct hd_struct *part)
 #define DISK_PITER_REVERSE      (1 << 0) /* iterate in the reverse direction */
 #define DISK_PITER_INCL_EMPTY   (1 << 1) /* include 0-sized parts */
 #define DISK_PITER_INCL_PART0   (1 << 2) /* include partition 0 */
+#define DISK_PITER_INCL_EMPTY_PART0 (1 << 3) /* include empty partition 0 */
 
 struct disk_part_iter {
         struct gendisk          *disk;