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Commit 81744ee4 authored by Martin K. Petersen's avatar Martin K. Petersen Committed by Jens Axboe
Browse files

block: Fix incorrect alignment offset reporting and update documentation 



queue_sector_alignment_offset returned the wrong value which caused
partitions to report an incorrect alignment_offset.  Since offset
alignment calculation is needed several places it has been split into a
separate helper function.  The topology stacking function has been
updated accordingly.

Furthermore, comments have been added to clarify how the stacking
function works.

Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
Tested-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 2f7a2d89

block/blk-settings.c

+33 −11
Original line number Diff line number Diff line
@@ -505,20 +505,30 @@ static unsigned int lcm(unsigned int a, unsigned int b) 


/**

 * blk_stack_limits - adjust queue_limits for stacked devices

 * @t:	the stacking driver limits (top)

 * @b:  the underlying queue limits (bottom)

 * @t:	the stacking driver limits (top device)

 * @b:  the underlying queue limits (bottom, component device)

 * @offset:  offset to beginning of data within component device

 *

 * Description:

 *    Merges two queue_limit structs.  Returns 0 if alignment didn't

 *    change.  Returns -1 if adding the bottom device caused

 *    misalignment.

 *    This function is used by stacking drivers like MD and DM to ensure

 *    that all component devices have compatible block sizes and

 *    alignments.  The stacking driver must provide a queue_limits

 *    struct (top) and then iteratively call the stacking function for

 *    all component (bottom) devices.  The stacking function will

 *    attempt to combine the values and ensure proper alignment.

 *

 *    Returns 0 if the top and bottom queue_limits are compatible.  The

 *    top device's block sizes and alignment offsets may be adjusted to

 *    ensure alignment with the bottom device. If no compatible sizes

 *    and alignments exist, -1 is returned and the resulting top

 *    queue_limits will have the misaligned flag set to indicate that

 *    the alignment_offset is undefined.

 */

int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,

		     sector_t offset)

{

	sector_t alignment;

	unsigned int top, bottom, granularity;

	unsigned int top, bottom;



	t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);

	t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
@@ -536,15 +546,18 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b, 
	t->max_segment_size = min_not_zero(t->max_segment_size,

					   b->max_segment_size);



	granularity = max(b->physical_block_size, b->io_min);

	alignment = b->alignment_offset - (offset & (granularity - 1));

	alignment = queue_limit_alignment_offset(b, offset);



	/* Bottom device has different alignment.  Check that it is

	 * compatible with the current top alignment.

	 */

	if (t->alignment_offset != alignment) {



		top = max(t->physical_block_size, t->io_min)

			+ t->alignment_offset;

		bottom = granularity + alignment;

		bottom = max(b->physical_block_size, b->io_min) + alignment;



		/* Verify that top and bottom intervals line up */

		if (max(top, bottom) & (min(top, bottom) - 1))

			t->misaligned = 1;

	}
@@ -561,32 +574,39 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b, 
	t->no_cluster |= b->no_cluster;

	t->discard_zeroes_data &= b->discard_zeroes_data;



	/* Physical block size a multiple of the logical block size? */

	if (t->physical_block_size & (t->logical_block_size - 1)) {

		t->physical_block_size = t->logical_block_size;

		t->misaligned = 1;

	}



	/* Minimum I/O a multiple of the physical block size? */

	if (t->io_min & (t->physical_block_size - 1)) {

		t->io_min = t->physical_block_size;

		t->misaligned = 1;

	}



	/* Optimal I/O a multiple of the physical block size? */

	if (t->io_opt & (t->physical_block_size - 1)) {

		t->io_opt = 0;

		t->misaligned = 1;

	}



	/* Find lowest common alignment_offset */

	t->alignment_offset = lcm(t->alignment_offset, alignment)

		& (max(t->physical_block_size, t->io_min) - 1);



	/* Verify that new alignment_offset is on a logical block boundary */

	if (t->alignment_offset & (t->logical_block_size - 1))

		t->misaligned = 1;



	/* Discard alignment and granularity */

	if (b->discard_granularity) {

		unsigned int granularity = b->discard_granularity;

		offset &= granularity - 1;



		alignment = b->discard_alignment -

			(offset & (b->discard_granularity - 1));

		alignment = (granularity + b->discard_alignment - offset)

			& (granularity - 1);



		if (t->discard_granularity != 0 &&

		    t->discard_alignment != alignment) {
@@ -598,6 +618,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b, 
				t->discard_misaligned = 1;

		}



		t->max_discard_sectors = min_not_zero(t->max_discard_sectors,

						      b->max_discard_sectors);

		t->discard_granularity = max(t->discard_granularity,

					     b->discard_granularity);

		t->discard_alignment = lcm(t->discard_alignment, alignment) &

include/linux/blkdev.h

+9 −2
Original line number Diff line number Diff line
@@ -1116,11 +1116,18 @@ static inline int queue_alignment_offset(struct request_queue *q) 
	return q->limits.alignment_offset;

}



static inline int queue_limit_alignment_offset(struct queue_limits *lim, sector_t offset)

{

	unsigned int granularity = max(lim->physical_block_size, lim->io_min);



	offset &= granularity - 1;

	return (granularity + lim->alignment_offset - offset) & (granularity - 1);

}



static inline int queue_sector_alignment_offset(struct request_queue *q,

						sector_t sector)

{

	return ((sector << 9) - q->limits.alignment_offset)

		& (q->limits.io_min - 1);

	return queue_limit_alignment_offset(&q->limits, sector << 9);

}



static inline int bdev_alignment_offset(struct block_device *bdev)