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@xxxxxxxxxxxxxxx>
---
drivers/md/linear.c | 35 +++++++++++++++++------------------
include/linux/raid/linear.h | 6 ++++--
2 files changed, 21 insertions(+), 20 deletions(-)
diff --git a/drivers/md/linear.c b/drivers/md/linear.c
index 441b7fa..71ffebd 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++;
@@ -162,25 +161,25 @@ 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++;
}
}
/*
@@ -192,9 +191,9 @@ 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);
}
@@ -219,7 +218,7 @@ 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)
@@ -228,12 +227,12 @@ 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 87090e9..f38b9c5 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];
};
--
1.5.4.3
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