On 04/04/2016 03:00 AM, Hannes Reinecke wrote:
The queue limits already have a 'chunk_sectors' setting, so
we should be presenting it via sysfs.
This patch does more than exporting chunk_sectors via sysfs. It also
makes that parameter configurable. Please mention this in the patch
description.
My understanding of the block drivers that call
blk_queue_chunk_sectors() is that increasing the chunk_sectors parameter
will break these drivers. I think the single queue_limits.chunk_sectors
parameter needs to be converted into two parameters:
- The value set by the block driver by calling
blk_queue_chunk_sectors().
- The value configured from user space through sysfs.
This will allow to ensure that the chunk_sectors parameter can be
increased from user space and also that it cannot be decreased.
+static ssize_t
+queue_chunk_sectors_store(struct request_queue *q, const char *page, size_t count)
+{
+ unsigned long chunk_sectors;
+
+ ssize_t ret = queue_var_store(&chunk_sectors, page, count);
+ if (ret < 0)
+ return ret;
+ spin_lock_irq(q->queue_lock);
+ blk_queue_chunk_sectors(q, chunk_sectors);
+ spin_unlock_irq(q->queue_lock);
+
+ return ret;
+}
In blk_queue_chunk_sectors() I found the following:
BUG_ON(!is_power_of_2(chunk_sectors));
Please make sure that this BUG_ON() cannot be triggered from user space.
Additionally, an update for Documentation/block/queue-sysfs.txt is
missing from this patch.
Bart.
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