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

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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
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6
include/linux/raid/linear.h
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@@ -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];
};