md/raid6: remove expectation that Q device is immediately after P device.

Code currently assumes that the devices in a raid6 stripe are
  0 1 ... N-1 P Q
in some rotated order.  We will shortly add new layouts in which
this strict pattern is broken.
So remove this expectation.  We still assume that the data disks
are roughly in-order.  However P and Q can be inserted anywhere within
that order.

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

1 files changed, 124 insertions, 87 deletions

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c33073fe7426..cb3e157b52d3 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -133,12 +133,36 @@ static inline void raid5_set_bi_hw_segments(struct bio *bio, unsigned int cnt)
         bio->bi_phys_segments = raid5_bi_phys_segments(bio) || (cnt << 16);
 }
 
+/* Find first data disk in a raid6 stripe */
+static inline int raid6_d0(struct stripe_head *sh)
+{
+        if (sh->qd_idx == sh->disks - 1)
+                return 0;
+        else
+                return sh->qd_idx + 1;
+}
 static inline int raid6_next_disk(int disk, int raid_disks)
 {
         disk++;
         return (disk < raid_disks) ? disk : 0;
 }
 
+/* When walking through the disks in a raid5, starting at raid6_d0,
+ * We need to map each disk to a 'slot', where the data disks are slot
+ * 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)
+{
+        int slot;
+        if (idx == sh->pd_idx)
+                return sh->disks - 2;
+        if (idx == sh->qd_idx)
+                return sh->disks - 1;
+        slot = (*count)++;
+        return slot;
+}
+
 static void return_io(struct bio *return_bi)
 {
         struct bio *bi = return_bi;
@@ -196,6 +220,7 @@ static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
                 }
         }
 }
+
 static void release_stripe(struct stripe_head *sh)
 {
         raid5_conf_t *conf = sh->raid_conf;
@@ -274,12 +299,14 @@ static int grow_buffers(struct stripe_head *sh, int num)
 }
 
 static void raid5_build_block(struct stripe_head *sh, int i);
-static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int previous);
+static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int previous,
+                           int *qd_idx);
 
 static void init_stripe(struct stripe_head *sh, sector_t sector, int previous)
 {
         raid5_conf_t *conf = sh->raid_conf;
         int i;
+        int qd_idx;
 
         BUG_ON(atomic_read(&sh->count) != 0);
         BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
@@ -293,7 +320,8 @@ static void init_stripe(struct stripe_head *sh, sector_t sector, int previous)
 
         sh->disks = previous ? conf->previous_raid_disks : conf->raid_disks;
         sh->sector = sector;
-        sh->pd_idx = stripe_to_pdidx(sector, conf, previous);
+        sh->pd_idx = stripe_to_pdidx(sector, conf, previous, &qd_idx);
+        sh->qd_idx = qd_idx;
         sh->state = 0;
 
 
@@ -1235,7 +1263,7 @@ static void error(mddev_t *mddev, mdk_rdev_t *rdev)
  */
 static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
                                      int previous,
-                                     int *dd_idx, int *pd_idx)
+                                     int *dd_idx, int *pd_idx, int *qd_idx)
 {
         long stripe;
         unsigned long chunk_number;
@@ -1268,6 +1296,7 @@ static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
         /*
          * Select the parity disk based on the user selected algorithm.
          */
+        *qd_idx = ~0;
         switch(conf->level) {
         case 4:
                 *pd_idx = data_disks;
@@ -1303,24 +1332,30 @@ static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
                 switch (conf->algorithm) {
                 case ALGORITHM_LEFT_ASYMMETRIC:
                         *pd_idx = raid_disks - 1 - (stripe % raid_disks);
-                        if (*pd_idx == raid_disks-1)
+                        *qd_idx = *pd_idx + 1;
+                        if (*pd_idx == raid_disks-1) {
                                 (*dd_idx)++;    /* Q D D D P */
-                        else if (*dd_idx >= *pd_idx)
+                                *qd_idx = 0;
+                        } else if (*dd_idx >= *pd_idx)
                                 (*dd_idx) += 2; /* D D P Q D */
                         break;
                 case ALGORITHM_RIGHT_ASYMMETRIC:
                         *pd_idx = stripe % raid_disks;
-                        if (*pd_idx == raid_disks-1)
+                        *qd_idx = *pd_idx + 1;
+                        if (*pd_idx == raid_disks-1) {
                                 (*dd_idx)++;    /* Q D D D P */
-                        else if (*dd_idx >= *pd_idx)
+                                *qd_idx = 0;
+                        } else if (*dd_idx >= *pd_idx)
                                 (*dd_idx) += 2; /* D D P Q D */
                         break;
                 case ALGORITHM_LEFT_SYMMETRIC:
                         *pd_idx = raid_disks - 1 - (stripe % raid_disks);
+                        *qd_idx = (*pd_idx + 1) % raid_disks;
                         *dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
                         break;
                 case ALGORITHM_RIGHT_SYMMETRIC:
                         *pd_idx = stripe % raid_disks;
+                        *qd_idx = (*pd_idx + 1) % raid_disks;
                         *dd_idx = (*pd_idx + 2 + *dd_idx) % raid_disks;
                         break;
                 default:
@@ -1347,7 +1382,7 @@ static sector_t compute_blocknr(struct stripe_head *sh, int i)
         int sectors_per_chunk = conf->chunk_size >> 9;
         sector_t stripe;
         int chunk_offset;
-        int chunk_number, dummy1, dummy2, dd_idx = i;
+        int chunk_number, dummy1, dummy2, dummy3, dd_idx = i;
         sector_t r_sector;
 
 
@@ -1378,7 +1413,7 @@ static sector_t compute_blocknr(struct stripe_head *sh, int i)
                 }
                 break;
         case 6:
-                if (i == raid6_next_disk(sh->pd_idx, raid_disks))
+                if (i == sh->qd_idx)
                         return 0; /* It is the Q disk */
                 switch (conf->algorithm) {
                 case ALGORITHM_LEFT_ASYMMETRIC:
@@ -1411,7 +1446,7 @@ static sector_t compute_blocknr(struct stripe_head *sh, int i)
 
         check = raid5_compute_sector(conf, r_sector,
                                      (raid_disks != conf->raid_disks),
-                                     &dummy1, &dummy2);
+                                     &dummy1, &dummy2, &dummy3);
         if (check != sh->sector || dummy1 != dd_idx || dummy2 != sh->pd_idx) {
                 printk(KERN_ERR "compute_blocknr: map not correct\n");
                 return 0;
@@ -1480,13 +1515,14 @@ static void copy_data(int frombio, struct bio *bio,
 static void compute_parity6(struct stripe_head *sh, int method)
 {
         raid5_conf_t *conf = sh->raid_conf;
-        int i, pd_idx = sh->pd_idx, qd_idx, d0_idx, disks = sh->disks, count;
+        int i, pd_idx, qd_idx, d0_idx, disks = sh->disks, count;
         struct bio *chosen;
         /**** FIX THIS: This could be very bad if disks is close to 256 ****/
         void *ptrs[disks];
 
-        qd_idx = raid6_next_disk(pd_idx, disks);
-        d0_idx = raid6_next_disk(qd_idx, disks);
+        pd_idx = sh->pd_idx;
+        qd_idx = sh->qd_idx;
+        d0_idx = raid6_d0(sh);
 
         pr_debug("compute_parity, stripe %llu, method %d\n",
                 (unsigned long long)sh->sector, method);
@@ -1524,22 +1560,22 @@ static void compute_parity6(struct stripe_head *sh, int method)
                         set_bit(R5_UPTODATE, &sh->dev[i].flags);
                 }
 
-//      switch(method) {
-//      case RECONSTRUCT_WRITE:
-//      case CHECK_PARITY:
-//      case UPDATE_PARITY:
-                /* Note that unlike RAID-5, the ordering of the disks matters greatly. */
-                /* FIX: Is this ordering of drives even remotely optimal? */
-                count = 0;
-                i = d0_idx;
-                do {
-                        ptrs[count++] = page_address(sh->dev[i].page);
-                        if (count <= disks-2 && !test_bit(R5_UPTODATE, &sh->dev[i].flags))
-                                printk("block %d/%d not uptodate on parity calc\n", i,count);
-                        i = raid6_next_disk(i, disks);
-                } while ( i != d0_idx );
-//              break;
-//      }
+        /* Note that unlike RAID-5, the ordering of the disks matters greatly.*/
+        /* FIX: Is this ordering of drives even remotely optimal? */
+        count = 0;
+        i = d0_idx;
+        do {
+                int slot = raid6_idx_to_slot(i, sh, &count);
+                ptrs[slot] = page_address(sh->dev[i].page);
+                if (slot < sh->disks - 2 &&
+                    !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);
 
         raid6_call.gen_syndrome(disks, STRIPE_SIZE, ptrs);
 
@@ -1563,8 +1599,7 @@ static void compute_block_1(struct stripe_head *sh, int dd_idx, int nozero)
 {
         int i, count, disks = sh->disks;
         void *ptr[MAX_XOR_BLOCKS], *dest, *p;
-        int pd_idx = sh->pd_idx;
-        int qd_idx = raid6_next_disk(pd_idx, disks);
+        int qd_idx = sh->qd_idx;
 
         pr_debug("compute_block_1, stripe %llu, idx %d\n",
                 (unsigned long long)sh->sector, dd_idx);
@@ -1600,21 +1635,31 @@ 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 pd_idx = sh->pd_idx;
-        int qd_idx = raid6_next_disk(pd_idx, disks);
-        int d0_idx = raid6_next_disk(qd_idx, disks);
-        int faila, failb;
+        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];
 
-        /* faila and failb are disk numbers relative to d0_idx */
-        /* pd_idx become disks-2 and qd_idx become disks-1 */
-        faila = (dd_idx1 < d0_idx) ? dd_idx1+(disks-d0_idx) : dd_idx1-d0_idx;
-        failb = (dd_idx2 < d0_idx) ? dd_idx2+(disks-d0_idx) : dd_idx2-d0_idx;
+        count = 0;
+        i = d0_idx;
+        do {
+                int slot;
+                slot = raid6_idx_to_slot(i, sh, &count);
+                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(faila == failb);
         if ( failb < faila ) { int tmp = faila; faila = failb; failb = tmp; }
 
         pr_debug("compute_block_2, stripe %llu, idx %d,%d (%d,%d)\n",
-               (unsigned long long)sh->sector, dd_idx1, dd_idx2, faila, failb);
+                 (unsigned long long)sh->sector, dd_idx1, dd_idx2,
+                 faila, failb);
 
         if ( failb == disks-1 ) {
                 /* Q disk is one of the missing disks */
@@ -1624,39 +1669,26 @@ static void compute_block_2(struct stripe_head *sh, int dd_idx1, int dd_idx2)
                         return;
                 } else {
                         /* We're missing D+Q; recompute D from P */
-                        compute_block_1(sh, (dd_idx1 == qd_idx) ? dd_idx2 : dd_idx1, 0);
+                        compute_block_1(sh, ((dd_idx1 == sh->qd_idx) ?
+                                             dd_idx2 : dd_idx1),
+                                        0);
                         compute_parity6(sh, UPDATE_PARITY); /* Is this necessary? */
                         return;
                 }
         }
 
-        /* We're missing D+P or D+D; build pointer table */
-        {
-                /**** FIX THIS: This could be very bad if disks is close to 256 ****/
-                void *ptrs[disks];
-
-                count = 0;
-                i = d0_idx;
-                do {
-                        ptrs[count++] = page_address(sh->dev[i].page);
-                        i = raid6_next_disk(i, disks);
-                        if (i != dd_idx1 && i != dd_idx2 &&
-                            !test_bit(R5_UPTODATE, &sh->dev[i].flags))
-                                printk("compute_2 with missing block %d/%d\n", count, i);
-                } while ( i != d0_idx );
-
-                if ( failb == disks-2 ) {
-                        /* We're missing D+P. */
-                        raid6_datap_recov(disks, STRIPE_SIZE, faila, ptrs);
-                } else {
-                        /* We're missing D+D. */
-                        raid6_2data_recov(disks, STRIPE_SIZE, faila, failb, ptrs);
-                }
-
-                /* Both the above update both missing blocks */
-                set_bit(R5_UPTODATE, &sh->dev[dd_idx1].flags);
-                set_bit(R5_UPTODATE, &sh->dev[dd_idx2].flags);
+        /* We're missing D+P or D+D; */
+        if (failb == disks-2) {
+                /* We're missing D+P. */
+                raid6_datap_recov(disks, STRIPE_SIZE, faila, ptrs);
+        } else {
+                /* We're missing D+D. */
+                raid6_2data_recov(disks, STRIPE_SIZE, faila, failb, ptrs);
         }
+
+        /* Both the above update both missing blocks */
+        set_bit(R5_UPTODATE, &sh->dev[dd_idx1].flags);
+        set_bit(R5_UPTODATE, &sh->dev[dd_idx2].flags);
 }
 
 static void
@@ -1811,7 +1843,8 @@ static int page_is_zero(struct page *p)
                 memcmp(a, a+4, STRIPE_SIZE-4)==0);
 }
 
-static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int previous)
+static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int previous,
+                           int *qd_idxp)
 {
         int sectors_per_chunk = conf->chunk_size >> 9;
         int pd_idx, dd_idx;
@@ -1822,7 +1855,7 @@ static int stripe_to_pdidx(sector_t stripe, raid5_conf_t *conf, int previous)
                              stripe * (disks - conf->max_degraded)
                              *sectors_per_chunk + chunk_offset,
                              previous,
-                             &dd_idx, &pd_idx);
+                             &dd_idx, &pd_idx, qd_idxp);
         return pd_idx;
 }
 
@@ -2481,12 +2514,13 @@ static void handle_stripe_expansion(raid5_conf_t *conf, struct stripe_head *sh,
         clear_bit(STRIPE_EXPAND_SOURCE, &sh->state);
         for (i = 0; i < sh->disks; i++)
                 if (i != sh->pd_idx && (!r6s || i != r6s->qd_idx)) {
-                        int dd_idx, pd_idx, j;
+                        int dd_idx, pd_idx, qd_idx, j;
                         struct stripe_head *sh2;
 
                         sector_t bn = compute_blocknr(sh, i);
-                        sector_t s = raid5_compute_sector(conf, bn, 0,
-                                                          &dd_idx, &pd_idx);
+                        sector_t s =
+                                raid5_compute_sector(conf, bn, 0,
+                                                     &dd_idx, &pd_idx, &qd_idx);
                         sh2 = get_active_stripe(conf, s, 0, 1);
                         if (sh2 == NULL)
                                 /* so far only the early blocks of this stripe
@@ -2510,8 +2544,7 @@ static void handle_stripe_expansion(raid5_conf_t *conf, struct stripe_head *sh,
                         set_bit(R5_UPTODATE, &sh2->dev[dd_idx].flags);
                         for (j = 0; j < conf->raid_disks; j++)
                                 if (j != sh2->pd_idx &&
-                                    (!r6s || j != raid6_next_disk(sh2->pd_idx,
-                                                                 sh2->disks)) &&
+                                    (!r6s || j != sh2->qd_idx) &&
                                     !test_bit(R5_Expanded, &sh2->dev[j].flags))
                                         break;
                         if (j == conf->raid_disks) {
@@ -2771,9 +2804,11 @@ static bool handle_stripe5(struct stripe_head *sh)
 
         if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state) &&
             !sh->reconstruct_state) {
+                int qd_idx;
                 /* Need to write out all blocks after computing parity */
                 sh->disks = conf->raid_disks;
-                sh->pd_idx = stripe_to_pdidx(sh->sector, conf, 0);
+                sh->pd_idx = stripe_to_pdidx(sh->sector, conf, 0, &qd_idx);
+                sh->qd_idx = qd_idx;
                 schedule_reconstruction5(sh, &s, 1, 1);
         } else if (s.expanded && !sh->reconstruct_state && s.locked == 0) {
                 clear_bit(STRIPE_EXPAND_READY, &sh->state);
@@ -2814,7 +2849,7 @@ static bool handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
         struct r5dev *dev, *pdev, *qdev;
         mdk_rdev_t *blocked_rdev = NULL;
 
-        r6s.qd_idx = raid6_next_disk(pd_idx, disks);
+        r6s.qd_idx = sh->qd_idx;
         pr_debug("handling stripe %llu, state=%#lx cnt=%d, "
                 "pd_idx=%d, qd_idx=%d\n",
                (unsigned long long)sh->sector, sh->state,
@@ -2990,8 +3025,10 @@ static bool handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
 
         if (s.expanded && test_bit(STRIPE_EXPANDING, &sh->state)) {
                 /* Need to write out all blocks after computing P&Q */
+                int qd_idx;
                 sh->disks = conf->raid_disks;
-                sh->pd_idx = stripe_to_pdidx(sh->sector, conf, 0);
+                sh->pd_idx = stripe_to_pdidx(sh->sector, conf, 0, &qd_idx);
+                sh->qd_idx = qd_idx;
                 compute_parity6(sh, RECONSTRUCT_WRITE);
                 for (i = conf->raid_disks ; i-- ;  ) {
                         set_bit(R5_LOCKED, &sh->dev[i].flags);
@@ -3263,7 +3300,7 @@ static int chunk_aligned_read(struct request_queue *q, struct bio * raid_bio)
 {
         mddev_t *mddev = q->queuedata;
         raid5_conf_t *conf = mddev_to_conf(mddev);
-        unsigned int dd_idx, pd_idx;
+        unsigned int dd_idx, pd_idx, qd_idx;
         struct bio* align_bi;
         mdk_rdev_t *rdev;
 
@@ -3288,7 +3325,7 @@ static int chunk_aligned_read(struct request_queue *q, struct bio * raid_bio)
          */
         align_bi->bi_sector =  raid5_compute_sector(conf, raid_bio->bi_sector,
                                                     0,
-                                                    &dd_idx, &pd_idx);
+                                                    &dd_idx, &pd_idx, &qd_idx);
 
         rcu_read_lock();
         rdev = rcu_dereference(conf->disks[dd_idx].rdev);
@@ -3380,7 +3417,7 @@ static int make_request(struct request_queue *q, struct bio * bi)
 {
         mddev_t *mddev = q->queuedata;
         raid5_conf_t *conf = mddev_to_conf(mddev);
-        unsigned int dd_idx, pd_idx;
+        int dd_idx, pd_idx, qd_idx;
         sector_t new_sector;
         sector_t logical_sector, last_sector;
         struct stripe_head *sh;
@@ -3447,7 +3484,7 @@ static int make_request(struct request_queue *q, struct bio * bi)
 
                 new_sector = raid5_compute_sector(conf, logical_sector,
                                                   previous,
-                                                  &dd_idx, &pd_idx);
+                                                  &dd_idx, &pd_idx, &qd_idx);
                 pr_debug("raid5: make_request, sector %llu logical %llu\n",
                         (unsigned long long)new_sector, 
                         (unsigned long long)logical_sector);
@@ -3535,7 +3572,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
          */
         raid5_conf_t *conf = (raid5_conf_t *) mddev->private;
         struct stripe_head *sh;
-        int pd_idx;
+        int pd_idx, qd_idx;
         sector_t first_sector, last_sector;
         int raid_disks = conf->previous_raid_disks;
         int data_disks = raid_disks - conf->max_degraded;
@@ -3598,7 +3635,7 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
                         if (j == sh->pd_idx)
                                 continue;
                         if (conf->level == 6 &&
-                            j == raid6_next_disk(sh->pd_idx, sh->disks))
+                            j == sh->qd_idx)
                                 continue;
                         s = compute_blocknr(sh, j);
                         if (s < mddev->array_sectors) {
@@ -3625,11 +3662,11 @@ static sector_t reshape_request(mddev_t *mddev, sector_t sector_nr, int *skipped
          */
         first_sector =
                 raid5_compute_sector(conf, sector_nr*(new_data_disks),
-                                     1, &dd_idx, &pd_idx);
+                                     1, &dd_idx, &pd_idx, &qd_idx);
         last_sector =
                 raid5_compute_sector(conf, ((sector_nr+conf->chunk_size/512)
                                             *(new_data_disks) - 1),
-                                     1, &dd_idx, &pd_idx);
+                                     1, &dd_idx, &pd_idx, &qd_idx);
         if (last_sector >= mddev->dev_sectors)
                 last_sector = mddev->dev_sectors - 1;
         while (first_sector <= last_sector) {
@@ -3764,7 +3801,7 @@ static int  retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
          * it will be only one 'dd_idx' and only need one call to raid5_compute_sector.
          */
         struct stripe_head *sh;
-        int dd_idx, pd_idx;
+        int dd_idx, pd_idx, qd_idx;
         sector_t sector, logical_sector, last_sector;
         int scnt = 0;
         int remaining;
@@ -3772,7 +3809,7 @@ static int  retry_aligned_read(raid5_conf_t *conf, struct bio *raid_bio)
 
         logical_sector = raid_bio->bi_sector & ~((sector_t)STRIPE_SECTORS-1);
         sector = raid5_compute_sector(conf, logical_sector,
-                                      0, &dd_idx, &pd_idx);
+                                      0, &dd_idx, &pd_idx, &qd_idx);
         last_sector = raid_bio->bi_sector + (raid_bio->bi_size>>9);
 
         for (; logical_sector < last_sector;