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Commit a79cfe12 authored by NeilBrown's avatar NeilBrown
Browse files

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: default avatarNeilBrown <neilb@suse.de>
parent 2c58f06e

drivers/md/raid5.c

+29 −9
Original line number Diff line number Diff line
@@ -2903,14 +2903,34 @@ static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s, 
	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 @@ static int need_this_block(struct stripe_head *sh, struct stripe_head_state *s, 
	      && 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;

}