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Subject[PATCH 1/3] block: Add blk_queue_copy_limits()
This patch is a preparation for the last patch in this patchset
which changes blk_set_default_limits() to set 0 to max_sectors.

dm uses blk_stack_limits() to merge limits of underlying devices
and copy the end result to the queue.
But if there's no underlying device (like 'zero' target),
max_sectors/max_hw_sectors are left unchanged from the default 0
and just copying it to the queue causes problems.

Provide blk_queue_copy_limits() to get a safe copy with
invalid values fixed-up.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: David Strand <dpstrand@gmail.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Alasdair G Kergon <agk@redhat.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
---
block/blk-settings.c | 28 ++++++++++++++++++++++++++++
include/linux/blkdev.h | 1 +
2 files changed, 29 insertions(+)
Index: linux-2.6.31.work/block/blk-settings.c
===================================================================
--- linux-2.6.31.work.orig/block/blk-settings.c
+++ linux-2.6.31.work/block/blk-settings.c
@@ -122,6 +122,34 @@ void blk_set_default_limits(struct queue
EXPORT_SYMBOL(blk_set_default_limits);

/**
+ * blk_queue_copy_limits - copy limits to queue
+ * @q: the request queue whose limits as a copy destination
+ * @lim: the queue_limits structure as a copy source
+ *
+ * Description:
+ * Copies a queue_limit struct contents to @q with fix-ups to
+ * invalid values.
+ */
+void blk_queue_copy_limits(struct request_queue *q, struct queue_limits
*lim)
+{
+ q->limits = *lim;
+
+ /*
+ * blk_set_default_limits() sets 0 to max_sectors/max_hw_sectors
+ * so that blk_stack_limits() appropriately propagate the values
+ * of lower-stack by min_not_zero().
+ * However, if the default value 0 is unchanged (e.g. the stacking
+ * device is virtual and has no underlying device), it results
+ * in unusable device.
+ * Check if max_sectors/max_hw_sectors have non-zero values,
+ * and set SAFE_MAX_SECTORS if they do.
+ */
+ if (q->limits.max_sectors == 0 || q->limits.max_hw_sectors == 0)
+ blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
+}
+EXPORT_SYMBOL(blk_queue_copy_limits);
+
+/**
* blk_queue_make_request - define an alternate make_request function
for a device
* @q: the request queue for the device to be affected
* @mfn: the alternate make_request function
Index: linux-2.6.31.work/include/linux/blkdev.h
===================================================================
--- linux-2.6.31.work.orig/include/linux/blkdev.h
+++ linux-2.6.31.work/include/linux/blkdev.h
@@ -917,6 +917,7 @@ extern void blk_limits_io_min(struct que
extern void blk_queue_io_min(struct request_queue *q, unsigned int min);
extern void blk_queue_io_opt(struct request_queue *q, unsigned int opt);
extern void blk_set_default_limits(struct queue_limits *lim);
+extern void blk_queue_copy_limits(struct request_queue *q, struct
queue_limits *lim);
extern int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
sector_t offset);
extern void disk_stack_limits(struct gendisk *disk, struct block_device
*bdev,

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