block: export blk_validate_limits

While block drivers do the validation as part of committing them to the
queue, users that use the limit outside of a block device context have
to validate the limits and fill in the calculated values as well.

So far btrfs is the only user of queue limits without a block device,
and it has gotten away with that more or less by accident.  But with
commit 559218d ("block: pre-calculate max_zone_append_sectors")
this became fatal for setups that have small max zone append size,
as it won't be limited now.

Export blk_validate_limits so that it can be called directly from btrfs.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Christoph Hellwig

block/blk-settings.c

@@ -222,7 +222,7 @@ static void blk_validate_atomic_write_limits(struct queue_limits *lim)
  * Check that the limits in lim are valid, initialize defaults for unset
  * values, and cap values based on others where needed.
  */
-static int blk_validate_limits(struct queue_limits *lim)
+int blk_validate_limits(struct queue_limits *lim)
 {
 	unsigned int max_hw_sectors;
 	unsigned int logical_block_sectors;
@@ -365,6 +365,7 @@ static int blk_validate_limits(struct queue_limits *lim)
 		return err;
 	return blk_validate_zoned_limits(lim);
 }
+EXPORT_SYMBOL_GPL(blk_validate_limits);
 
 /*
  * Set the default limits for a newly allocated queue.  @lim contains the

include/linux/blkdev.h

@@ -948,6 +948,7 @@ queue_limits_start_update(struct request_queue *q)
 int queue_limits_commit_update(struct request_queue *q,
 		struct queue_limits *lim);
 int queue_limits_set(struct request_queue *q, struct queue_limits *lim);
+int blk_validate_limits(struct queue_limits *lim);
 
 /**
  * queue_limits_cancel_update - cancel an atomic update of queue limits