md: Convert remaining 1k representations in linear.c to sectors.

This patch renames hash_spacing and preshift to  spacing and
sector_shift respectively with the following change of semantics:

Case 1: (sizeof(sector_t) <= sizeof(u32)).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In this case, we have sector_shift = preshift = 0 and spacing =
2 * hash_spacing.

Hence, the index for the hash table which is computed by the new code
in which_dev() as sector / spacing equals the old value which was
(sector/2) / hash_spacing.

Note also that the value of nb_zone stays the same because both sz
and base double.

Case 2: (sizeof(sector_t) > sizeof(u32)).
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(aka the shifting dance case). Here we have sector_shift = preshift +
1 and

spacing = 2 * hash_spacing

during the computation of nb_zone and curr_sector, but

spacing = hash_spacing

in which_dev() because in the last hunk of the patch for linear.c we
shift down conf->spacing (= 2 * hash_spacing) by one more bit than
in the old code.

Hence in the computation of nb_zone, sz and base have the same value
as before, so nb_zone is not affected. Also curr_sector in the next
hunk stays the same.

In which_dev() the hash table index is computed as

(sector >> sector_shift) / spacing

In view of sector_shift = preshift + 1 and spacing = hash_spacing,
this equals

((sector/2) >> preshift) / hash_spacing

which is the value computed by the old code.

Signed-off-by: Andre Noll <maan@systemlinux.org>
Signed-off-by: NeilBrown <neilb@suse.de>

2 files changed, 21 insertions, 20 deletions

diff --git a/drivers/md/linear.c b/drivers/md/linear.c
index 13e928bde7cd..09a64b9cbde8 100644
--- a/drivers/md/linear.c
+++ b/drivers/md/linear.c
@@ -33,14 +33,13 @@ static inline dev_info_t *which_dev(mddev_t *mddev, sector_t sector)
 {
         dev_info_t *hash;
         linear_conf_t *conf = mddev_to_conf(mddev);
-        sector_t block = sector >> 1;
 
         /*
          * sector_div(a,b) returns the remainer and sets a to a/b
          */
-        block >>= conf->preshift;
-        (void)sector_div(block, conf->hash_spacing);
-        hash = conf->hash_table[block];
+        sector >>= conf->sector_shift;
+        (void)sector_div(sector, conf->spacing);
+        hash = conf->hash_table[sector];
 
         while (sector >= hash->num_sectors + hash->start_sector)
                 hash++;
@@ -164,25 +163,25 @@ static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
          * that is larger than min_sectors and use the size of that as
          * the actual spacing
          */
-        conf->hash_spacing = conf->array_sectors / 2;
+        conf->spacing = conf->array_sectors;
         for (i=0; i < cnt-1 ; i++) {
                 sector_t tmp = 0;
                 int j;
                 for (j = i; j < cnt - 1 && tmp < min_sectors; j++)
                         tmp += conf->disks[j].num_sectors;
-                if (tmp >= min_sectors && tmp < conf->hash_spacing * 2)
-                        conf->hash_spacing = tmp / 2;
+                if (tmp >= min_sectors && tmp < conf->spacing)
+                        conf->spacing = tmp;
         }
 
-        /* hash_spacing may be too large for sector_div to work with,
+        /* spacing may be too large for sector_div to work with,
          * so we might need to pre-shift
          */
-        conf->preshift = 0;
+        conf->sector_shift = 0;
         if (sizeof(sector_t) > sizeof(u32)) {
-                sector_t space = conf->hash_spacing;
+                sector_t space = conf->spacing;
                 while (space > (sector_t)(~(u32)0)) {
                         space >>= 1;
-                        conf->preshift++;
+                        conf->sector_shift++;
                 }
         }
         /*
@@ -194,9 +193,9 @@ static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
                 unsigned round;
                 unsigned long base;
 
-                sz = conf->array_sectors >> (conf->preshift + 1);
+                sz = conf->array_sectors >> conf->sector_shift;
                 sz += 1; /* force round-up */
-                base = conf->hash_spacing >> conf->preshift;
+                base = conf->spacing >> conf->sector_shift;
                 round = sector_div(sz, base);
                 nb_zone = sz + (round ? 1 : 0);
         }
@@ -221,7 +220,7 @@ static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
         i = 0;
         for (curr_sector = 0;
              curr_sector < conf->array_sectors;
-             curr_sector += conf->hash_spacing * 2) {
+             curr_sector += conf->spacing) {
 
                 while (i < raid_disks-1 &&
                        curr_sector >= conf->disks[i+1].start_sector)
@@ -230,12 +229,12 @@ static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
                 *table ++ = conf->disks + i;
         }
 
-        if (conf->preshift) {
-                conf->hash_spacing >>= conf->preshift;
-                /* round hash_spacing up so that when we divide by it,
+        if (conf->sector_shift) {
+                conf->spacing >>= conf->sector_shift;
+                /* round spacing up so that when we divide by it,
                  * we err on the side of "too-low", which is safest.
                  */
-                conf->hash_spacing++;
+                conf->spacing++;
         }
 
         BUG_ON(table - conf->hash_table > nb_zone);
diff --git a/include/linux/raid/linear.h b/include/linux/raid/linear.h
index 87090e98529f..f38b9c586afb 100644
--- a/include/linux/raid/linear.h
+++ b/include/linux/raid/linear.h
@@ -15,9 +15,11 @@ struct linear_private_data
 {
         struct linear_private_data *prev;       /* earlier version */
         dev_info_t              **hash_table;
-        sector_t                hash_spacing;
+        sector_t                spacing;
         sector_t                array_sectors;
-        int                     preshift; /* shift before dividing by hash_spacing */
+        int                     sector_shift;   /* shift before dividing
+                                                 * by spacing
+                                                 */
         dev_info_t              disks[0];
 };