linux-kernel - [PATCH] Allow changing max_sectors

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Date:	Tue, 1 Sep 2009 18:15:45 +0530
From:	Nikanth Karthikesan <knikanth@...e.de>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] Allow changing max_sectors_kb above the default 512

The patch "block: Use accessor functions for queue limits"
(ae03bf639a5027d27270123f5f6e3ee6a412781d) changed queue_max_sectors_store()
to use blk_queue_max_sectors() instead of directly assigning the value.

But blk_queue_max_sectors() differs a bit
1. It sets both max_sectors_kb, and max_hw_sectors_kb
2. Never allows one to change max_sectors_kb above BLK_DEF_MAX_SECTORS. If one
specifies a value greater then max_hw_sectors is set to that value but
max_sectors is set to BLK_DEF_MAX_SECTORS

I am not sure whether blk_queue_max_sectors() should be changed, as it seems
to be that way for a long time. And there may be callers dependent on that
behaviour.

This patch simply reverts to the older way of directly assigning the value to
max_sectors as it was before.

Signed-off-by: Nikanth Karthikesan <knikanth@...e.de>

---

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 418d636..d3aa2aa 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -133,7 +133,7 @@ queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
 		return -EINVAL;

 	spin_lock_irq(q->queue_lock);
-	blk_queue_max_sectors(q, max_sectors_kb << 1);
+	q->limits.max_sectors = max_sectors_kb << 1;
 	spin_unlock_irq(q->queue_lock);

 	return ret;
--
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