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SubjectRe: [PATCH 1/1] mtd: mtd_blkdevs: handle REQ_FLUSH request and do explicit flush of writeback buffer
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On Fri, Mar 7, 2014 at 3:44 PM, Brian Norris
<computersforpeace@gmail.com> wrote:
> On Thu, Jan 02, 2014 at 01:21:21AM +0900, Roman Pen wrote:
>> From: Roman Peniaev <r.peniaev@gmail.com>
>>
>> mtd_blkdevs is device with volatile cache (writeback buffer), so it should support
>> REQ_FLUSH to do explicit flush.
>>
>> Without this patch 'sync' does not guarantee that writeback buffer will be flushed
>> on disk in case of power off, e.g.:
>>
>> $ cp some_file /mnt
>> $ sync
>>
>> ### POWER OFF
>>
>> In case of this sequence writeback buffer will not be flushed on disk.
>>
>> This patch fixes this behaviour and explicitly reports to block layer that flush
>> requests are being supported.
>>
>> Signed-off-by: Roman Peniaev <r.peniaev@gmail.com>
>> CC: David Woodhouse <dwmw2@infradead.org>
>> CC: linux-mtd@lists.infradead.org
>> CC: linux-kernel@vger.kernel.org
>> ---
>> drivers/mtd/mtd_blkdevs.c | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
>> index 5073cbc..feafe5c 100644
>> --- a/drivers/mtd/mtd_blkdevs.c
>> +++ b/drivers/mtd/mtd_blkdevs.c
>> @@ -89,6 +89,12 @@ static int do_blktrans_request(struct mtd_blktrans_ops *tr,
>> if (req->cmd_type != REQ_TYPE_FS)
>> return -EIO;
>>
>> + if (req->cmd_flags & REQ_FLUSH) {
>> + if (tr->flush)
>> + return tr->flush(dev);
>> + return 0;
>> + }
>> +
>> if (blk_rq_pos(req) + blk_rq_cur_sectors(req) >
>> get_capacity(req->rq_disk))
>> return -EIO;
>> @@ -409,6 +415,8 @@ int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
>> if (!new->rq)
>> goto error3;
>>
>> + blk_queue_flush(new->rq, REQ_FLUSH);
>
> How about only registering the flush command if we support it? So:
>
> if (tr->flush)
> blk_queue_flush(new->rq, REQ_FLUSH);

Yep, that's better.
Will send v2.

--
Roman

>
> Then you can probably also change the earlier hunk to the following, no?
>
> if (req->cmd_flags & REQ_FLUSH)
> return tr->flush(dev);
>
>> +
>> new->rq->queuedata = new;
>> blk_queue_logical_block_size(new->rq, tr->blksize);
>>
>
> Brian


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