On 04/14/2016 09:09 PM, Bart Van Assche wrote:
> 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.
>
Ah, right.
Actually, making the sysfs attribute writeable is a leftover from
the original (debugging) patchset, so I'll be removing it from the
next iteration of this patchset.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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