Commit ab5bd5cb authored by Andre Noll's avatar Andre Noll Committed by NeilBrown
Browse files

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: default avatarAndre Noll <maan@systemlinux.org>
Signed-off-by: default avatarNeilBrown <neilb@suse.de>
parent 23242fbb

drivers/md/linear.c

+17 −18
Original line number Diff line number Diff line
@@ -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);

include/linux/raid/linear.h

+4 −2
Original line number Diff line number Diff line
@@ -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];

};

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