md: simplify md_seq_ops

Before this patch, the implementation is hacky and hard to understand:

1) md_seq_start set pos to 1;
2) md_seq_show found pos is 1, then print Personalities;
3) md_seq_next found pos is 1, then it update pos to the first mddev;
4) md_seq_show found pos is not 1 or 2, show mddev;
5) md_seq_next found pos is not 1 or 2, update pos to next mddev;
6) loop 4-5 until the last mddev, then md_seq_next update pos to 2;
7) md_seq_show found pos is 2, then print unused devices;
8) md_seq_next found pos is 2, stop;

This patch remove the magic value and use seq_list_start/next/stop()
directly, and move printing "Personalities" to md_seq_start(),
"unsed devices" to md_seq_stop():

1) md_seq_start print Personalities, and then set pos to first mddev;
2) md_seq_show show mddev;
3) md_seq_next update pos to next mddev;
4) loop 2-3 until the last mddev;
5) md_seq_stop print unsed devices;

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230927061241.1552837-3-yukuai1@huaweicloud.com

diff --git a/drivers/md/md.c b/drivers/md/md.c
index aad91cd72a0600572338ad32e42013974f1abca4..38a6767c65b17fe201b49afcd0ce68f61dc73ba9 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8213,105 +8213,46 @@ static int status_resync(struct seq_file *seq, struct mddev *mddev)
 }
 
 static void *md_seq_start(struct seq_file *seq, loff_t *pos)
+       __acquires(&all_mddevs_lock)
 {
-       struct list_head *tmp;
-       loff_t l = *pos;
-       struct mddev *mddev;
+       struct md_personality *pers;
 
-       if (l == 0x10000) {
-               ++*pos;
-               return (void *)2;
-       }
-       if (l > 0x10000)
-               return NULL;
-       if (!l--)
-               /* header */
-               return (void*)1;
+       seq_puts(seq, "Personalities : ");
+       spin_lock(&pers_lock);
+       list_for_each_entry(pers, &pers_list, list)
+               seq_printf(seq, "[%s] ", pers->name);
+
+       spin_unlock(&pers_lock);
+       seq_puts(seq, "\n");
+       seq->poll_event = atomic_read(&md_event_count);
 
        spin_lock(&all_mddevs_lock);
-       list_for_each(tmp,&all_mddevs)
-               if (!l--) {
-                       mddev = list_entry(tmp, struct mddev, all_mddevs);
-                       if (!mddev_get(mddev))
-                               continue;
-                       spin_unlock(&all_mddevs_lock);
-                       return mddev;
-               }
-       spin_unlock(&all_mddevs_lock);
-       if (!l--)
-               return (void*)2;/* tail */
-       return NULL;
+
+       return seq_list_start(&all_mddevs, *pos);
 }
 
 static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-       struct list_head *tmp;
-       struct mddev *next_mddev, *mddev = v;
-       struct mddev *to_put = NULL;
-
-       ++*pos;
-       if (v == (void*)2)
-               return NULL;
-
-       spin_lock(&all_mddevs_lock);
-       if (v == (void*)1) {
-               tmp = all_mddevs.next;
-       } else {
-               to_put = mddev;
-               tmp = mddev->all_mddevs.next;
-       }
-
-       for (;;) {
-               if (tmp == &all_mddevs) {
-                       next_mddev = (void*)2;
-                       *pos = 0x10000;
-                       break;
-               }
-               next_mddev = list_entry(tmp, struct mddev, all_mddevs);
-               if (mddev_get(next_mddev))
-                       break;
-               mddev = next_mddev;
-               tmp = mddev->all_mddevs.next;
-       }
-       spin_unlock(&all_mddevs_lock);
-
-       if (to_put)
-               mddev_put(to_put);
-       return next_mddev;
-
+       return seq_list_next(v, &all_mddevs, pos);
 }
 
 static void md_seq_stop(struct seq_file *seq, void *v)
+       __releases(&all_mddevs_lock)
 {
-       struct mddev *mddev = v;
-
-       if (mddev && v != (void*)1 && v != (void*)2)
-               mddev_put(mddev);
+       status_unused(seq);
+       spin_unlock(&all_mddevs_lock);
 }
 
 static int md_seq_show(struct seq_file *seq, void *v)
 {
-       struct mddev *mddev = v;
+       struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
        sector_t sectors;
        struct md_rdev *rdev;
 
-       if (v == (void*)1) {
-               struct md_personality *pers;
-               seq_printf(seq, "Personalities : ");
-               spin_lock(&pers_lock);
-               list_for_each_entry(pers, &pers_list, list)
-                       seq_printf(seq, "[%s] ", pers->name);
-
-               spin_unlock(&pers_lock);
-               seq_printf(seq, "\n");
-               seq->poll_event = atomic_read(&md_event_count);
+       if (!mddev_get(mddev))
                return 0;
-       }
-       if (v == (void*)2) {
-               status_unused(seq);
-               return 0;
-       }
 
+       spin_unlock(&all_mddevs_lock);
        spin_lock(&mddev->lock);
        if (mddev->pers || mddev->raid_disks || !list_empty(&mddev->disks)) {
                seq_printf(seq, "%s : %sactive", mdname(mddev),
@@ -8382,6 +8323,9 @@ static int md_seq_show(struct seq_file *seq, void *v)
                seq_printf(seq, "\n");
        }
        spin_unlock(&mddev->lock);
+       spin_lock(&all_mddevs_lock);
+       if (atomic_dec_and_test(&mddev->active))
+               __mddev_put(mddev);
 
        return 0;
 }