btrfs: reada: ignore creating reada_extent for a non-existent device

For a non-existent device, old code bypasses adding it in dev's reada
queue.

And to solve problem of unfinished waitting in raid5/6,
commit 5fbc7c59fd22 ("Btrfs: fix unfinished readahead thread for
raid5/6 degraded mounting")
adding an exception for the first stripe, in short, the first
stripe will always be processed whether the device exists or not.

Actually we have a better way for the above request: just bypass
creation of the reada_extent for non-existent device, it will make
code simple and effective.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/reada.c b/fs/btrfs/reada.c
index 5bcd567..dd5f361 100644 (file)
--- a/fs/btrfs/reada.c
+++ b/fs/btrfs/reada.c
@@ -371,6 +371,11 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root,
                struct reada_zone *zone;
 
                dev = bbio->stripes[nzones].dev;
+
+               /* cannot read ahead on missing device. */
+                if (!dev->bdev)
+                       continue;
+
                zone = reada_find_zone(fs_info, dev, logical, bbio);
                if (!zone)
                        continue;
@@ -423,15 +428,9 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root,
                         */
                        continue;
                }
-               if (!dev->bdev) {
-                       /*
-                        * cannot read ahead on missing device, but for RAID5/6,
-                        * REQ_GET_READ_MIRRORS return 1. So don't skip missing
-                        * device for such case.
-                        */
-                       if (nzones > 1)
-                               continue;
-               }
+               if (!dev->bdev)
+                       continue;
+
                if (dev_replace_is_ongoing &&
                    dev == fs_info->dev_replace.tgtdev) {
                        /*