bcachefs: improve error message on too few devices for ec

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/ec.c b/fs/bcachefs/ec.c
index 46667fce6b699ed4679fd348a6c25251b8909912..cc76ae3d207384ca03eb97c54e3ebde2f2356e18 100644 (file)
--- a/fs/bcachefs/ec.c
+++ b/fs/bcachefs/ec.c
@@ -1728,10 +1728,12 @@ ec_new_stripe_head_alloc(struct bch_fs *c, unsigned disk_label,
 
        rcu_read_lock();
        h->devs = target_rw_devs(c, BCH_DATA_user, disk_label ? group_to_target(disk_label - 1) : 0);
+       unsigned nr_devs = dev_mask_nr(&h->devs);
 
        for_each_member_device_rcu(c, ca, &h->devs)
                if (!ca->mi.durability)
                        __clear_bit(ca->dev_idx, h->devs.d);
+       unsigned nr_devs_with_durability = dev_mask_nr(&h->devs);
 
        h->blocksize = pick_blocksize(c, &h->devs);
 
@@ -1745,9 +1747,20 @@ ec_new_stripe_head_alloc(struct bch_fs *c, unsigned disk_label,
         * If we only have redundancy + 1 devices, we're better off with just
         * replication:
         */
-       if (h->nr_active_devs < h->redundancy + 2)
-               bch_err(c, "insufficient devices available to create stripe (have %u, need %u) - mismatched bucket sizes?",
-                       h->nr_active_devs, h->redundancy + 2);
+       if (h->nr_active_devs < h->redundancy + 2) {
+               const char *err;
+
+               if (nr_devs < h->redundancy + 2)
+                       err = NULL;
+               else if (nr_devs_with_durability < h->redundancy + 2)
+                       err = "cannot use durability=0 devices";
+               else
+                       err = "mismatched bucket sizes";
+
+               if (err)
+                       bch_err(c, "insufficient devices available to create stripe (have %u, need %u): %s",
+                               h->nr_active_devs, h->redundancy + 2, err);
+       }
 
        list_add(&h->list, &c->ec_stripe_head_list);
        return h;