md/raid5: finish support for DDF/raid6

DDF requires RAID6 calculations over different devices in a different
order.
For md/raid6, we calculate over just the data devices, starting
immediately after the 'Q' block.
For ddf/raid6 we calculate over all devices, using zeros in place of
the P and Q blocks.

This requires unfortunately complex loops...

Signed-off-by: NeilBrown <neilb@suse.de>

2 files changed, 41 insertions, 18 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c1d94ed9718b..edbc80c4d346 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -136,6 +136,10 @@ static inline void raid5_set_bi_hw_segments(struct bio *bio, unsigned int cnt)
 /* Find first data disk in a raid6 stripe */
 static inline int raid6_d0(struct stripe_head *sh)
 {
+        if (sh->ddf_layout)
+                /* ddf always start from first device */
+                return 0;
+        /* md starts just after Q block */
         if (sh->qd_idx == sh->disks - 1)
                 return 0;
         else
@@ -152,13 +156,15 @@ static inline int raid6_next_disk(int disk, int raid_disks)
  * 0 .. raid_disks-3, the parity disk is raid_disks-2 and the Q disk
  * is raid_disks-1.  This help does that mapping.
  */
-static int raid6_idx_to_slot(int idx, struct stripe_head *sh, int *count)
+static int raid6_idx_to_slot(int idx, struct stripe_head *sh,
+                             int *count, int syndrome_disks)
 {
         int slot;
+
         if (idx == sh->pd_idx)
-                return sh->disks - 2;
+                return syndrome_disks;
         if (idx == sh->qd_idx)
-                return sh->disks - 1;
+                return syndrome_disks + 1;
         slot = (*count)++;
         return slot;
 }
@@ -1267,6 +1273,7 @@ static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
         unsigned long chunk_number;
         unsigned int chunk_offset;
         int pd_idx, qd_idx;
+        int ddf_layout = 0;
         sector_t new_sector;
         int sectors_per_chunk = conf->chunk_size >> 9;
         int raid_disks = previous ? conf->previous_raid_disks
@@ -1386,6 +1393,7 @@ static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
                                 qd_idx = 0;
                         } else if (*dd_idx >= pd_idx)
                                 (*dd_idx) += 2; /* D D P Q D */
+                        ddf_layout = 1;
                         break;
 
                 case ALGORITHM_ROTATING_N_RESTART:
@@ -1400,6 +1408,7 @@ static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
                                 qd_idx = 0;
                         } else if (*dd_idx >= pd_idx)
                                 (*dd_idx) += 2; /* D D P Q D */
+                        ddf_layout = 1;
                         break;
 
                 case ALGORITHM_ROTATING_N_CONTINUE:
@@ -1407,6 +1416,7 @@ static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
                         pd_idx = raid_disks - 1 - (stripe % raid_disks);
                         qd_idx = (pd_idx + raid_disks - 1) % raid_disks;
                         *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
+                        ddf_layout = 1;
                         break;
 
                 case ALGORITHM_LEFT_ASYMMETRIC_6:
@@ -1454,6 +1464,7 @@ static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
         if (sh) {
                 sh->pd_idx = pd_idx;
                 sh->qd_idx = qd_idx;
+                sh->ddf_layout = ddf_layout;
         }
         /*
          * Finally, compute the new sector number
@@ -1642,9 +1653,10 @@ static void compute_parity6(struct stripe_head *sh, int method)
 {
         raid5_conf_t *conf = sh->raid_conf;
         int i, pd_idx, qd_idx, d0_idx, disks = sh->disks, count;
+        int syndrome_disks = sh->ddf_layout ? disks : (disks - 2);
         struct bio *chosen;
         /**** FIX THIS: This could be very bad if disks is close to 256 ****/
-        void *ptrs[disks];
+        void *ptrs[syndrome_disks+2];
 
         pd_idx = sh->pd_idx;
         qd_idx = sh->qd_idx;
@@ -1687,23 +1699,28 @@ static void compute_parity6(struct stripe_head *sh, int method)
                 }
 
         /* Note that unlike RAID-5, the ordering of the disks matters greatly.*/
-        /* FIX: Is this ordering of drives even remotely optimal? */
+
+        for (i = 0; i < disks; i++)
+                ptrs[i] = (void *)raid6_empty_zero_page;
+
         count = 0;
         i = d0_idx;
         do {
-                int slot = raid6_idx_to_slot(i, sh, &count);
+                int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);
+
                 ptrs[slot] = page_address(sh->dev[i].page);
-                if (slot < sh->disks - 2 &&
+                if (slot < syndrome_disks &&
                     !test_bit(R5_UPTODATE, &sh->dev[i].flags)) {
                         printk(KERN_ERR "block %d/%d not uptodate "
                                "on parity calc\n", i, count);
                         BUG();
                 }
+
                 i = raid6_next_disk(i, disks);
         } while (i != d0_idx);
-        BUG_ON(count+2 != disks);
+        BUG_ON(count != syndrome_disks);
 
-        raid6_call.gen_syndrome(disks, STRIPE_SIZE, ptrs);
+        raid6_call.gen_syndrome(syndrome_disks+2, STRIPE_SIZE, ptrs);
 
         switch(method) {
         case RECONSTRUCT_WRITE:
@@ -1761,24 +1778,28 @@ static void compute_block_1(struct stripe_head *sh, int dd_idx, int nozero)
 static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
 {
         int i, count, disks = sh->disks;
+        int syndrome_disks = sh->ddf_layout ? disks : disks-2;
         int d0_idx = raid6_d0(sh);
         int faila = -1, failb = -1;
         /**** FIX THIS: This could be very bad if disks is close to 256 ****/
-        void *ptrs[disks];
+        void *ptrs[syndrome_disks+2];
 
+        for (i = 0; i < disks ; i++)
+                ptrs[i] = (void *)raid6_empty_zero_page;
         count = 0;
         i = d0_idx;
         do {
-                int slot;
-                slot = raid6_idx_to_slot(i, sh, &count);
+                int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);
+
                 ptrs[slot] = page_address(sh->dev[i].page);
+
                 if (i == dd_idx1)
                         faila = slot;
                 if (i == dd_idx2)
                         failb = slot;
                 i = raid6_next_disk(i, disks);
         } while (i != d0_idx);
-        BUG_ON(count+2 != disks);
+        BUG_ON(count != syndrome_disks);
 
         BUG_ON(faila == failb);
         if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }
@@ -1787,9 +1808,9 @@ static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
                  (unsigned long long)sh->sector, dd_idx1, dd_idx2,
                  faila, failb);
 
-        if ( failb == disks-1 ) {
+        if (failb == syndrome_disks+1) {
                 /* Q disk is one of the missing disks */
-                if ( faila == disks-2 ) {
+                if (faila == syndrome_disks) {
                         /* Missing P+Q, just recompute */
                         compute_parity6(sh, UPDATE_PARITY);
                         return;
@@ -1804,12 +1825,13 @@ static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
         }
 
         /* We're missing D+P or D+D; */
-        if (failb == disks-2) {
+        if (failb == syndrome_disks) {
                 /* We're missing D+P. */
-                raid6_datap_recov(disks, STRIPE_SIZE, faila, ptrs);
+                raid6_datap_recov(syndrome_disks+2, STRIPE_SIZE, faila, ptrs);
         } else {
                 /* We're missing D+D. */
-                raid6_2data_recov(disks, STRIPE_SIZE, faila, failb, ptrs);
+                raid6_2data_recov(syndrome_disks+2, STRIPE_SIZE, faila, failb,
+                                  ptrs);
         }
 
         /* Both the above update both missing blocks */
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 633d79289616..84456b1af204 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -201,6 +201,7 @@ struct stripe_head {
         sector_t                sector;         /* sector of this row */
         short                   pd_idx;         /* parity disk index */
         short                   qd_idx;         /* 'Q' disk index for raid6 */
+        short                   ddf_layout;/* use DDF ordering to calculate Q */
         unsigned long           state;          /* state flags */
         atomic_t                count;        /* nr of active thread/requests */
         spinlock_t              lock;