md/raid5: separate out the easy conditions in need_this_block.
Some of the conditions in need_this_block have very straight
forward motivation. Separate those out and document them.
Signed-off-by: NeilBrown <neilb@suse.de>
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 5a980fe..21c1e79 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2903,14 +2903,34 @@
struct r5dev *fdev[2] = { &sh->dev[s->failed_num[0]],
&sh->dev[s->failed_num[1]] };
- if (!test_bit(R5_LOCKED, &dev->flags) &&
- !test_bit(R5_UPTODATE, &dev->flags) &&
- (dev->toread ||
- (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
- s->syncing || s->expanding ||
- (s->replacing && want_replace(sh, disk_idx)) ||
- (s->failed >= 1 && fdev[0]->toread) ||
- (s->failed >= 2 && fdev[1]->toread) ||
+
+ if (test_bit(R5_LOCKED, &dev->flags) ||
+ test_bit(R5_UPTODATE, &dev->flags))
+ /* No point reading this as we already have it or have
+ * decided to get it.
+ */
+ return 0;
+
+ if (dev->toread ||
+ (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)))
+ /* We need this block to directly satisfy a request */
+ return 1;
+
+ if (s->syncing || s->expanding ||
+ (s->replacing && want_replace(sh, disk_idx)))
+ /* When syncing, or expanding we read everything.
+ * When replacing, we need the replaced block.
+ */
+ return 1;
+
+ if ((s->failed >= 1 && fdev[0]->toread) ||
+ (s->failed >= 2 && fdev[1]->toread))
+ /* If we want to read from a failed device, then
+ * we need to actually read every other device.
+ */
+ return 1;
+
+ if (
(sh->raid_conf->level <= 5 && s->failed && fdev[0]->towrite &&
(!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) &&
!test_bit(R5_OVERWRITE, &fdev[0]->flags)) ||
@@ -2919,7 +2939,7 @@
&& s->failed && s->to_write &&
(s->to_write - s->non_overwrite <
sh->raid_conf->raid_disks - sh->raid_conf->max_degraded) &&
- (!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)))))
+ (!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))))
return 1;
return 0;
}