dect
/
linux-2.6
Archived
13
0
Fork 0
Code Releases Activity

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>
This commit is contained in:
Andre Noll 2008-10-13 11:55:12 +11:00 committed by NeilBrown
parent 23242fbb47
commit ab5bd5cbc8
2 changed files with 21 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
drivers/md/linear.c
View File

@ -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);

6
include/linux/raid/linear.h
View File

@ -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];
};