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>
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