Boris Ostrovsky <boris.ostrov...@oracle.com> writes:
> On 11/03/2014 07:22 AM, Laszlo Ersek wrote:
>> On 10/27/14 14:44, Vitaly Kuznetsov wrote:
>>> Guard against issuing unsupported REQ_FUA and REQ_FLUSH was introduced
>>> in d11e61583 and was factored out into blkif_request_flush_valid() in
>>> 0f1ca65ee. However:
>>> 1) This check in incomplete. In case we negotiated to feature_flush =
>>> REQ_FLUSH
>>> and flush_op = BLKIF_OP_FLUSH_DISKCACHE (so FUA is unsupported) FUA
>>> request
>>> will still pass the check.
>>> 2) blkif_request_flush_valid() is misnamed. It is bool but returns true when
>>> the request is invalid.
>>> 3) When blkif_request_flush_valid() fails -EIO is being returned. It seems
>>> that
>>> -EOPNOTSUPP is more appropriate here.
>>> Fix all of the above issues.
>>>
>>> This patch is based on the original patch by Laszlo Ersek and a comment by
>>> Jeff Moyer.
>>>
>>> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
>>> ---
>>> drivers/block/xen-blkfront.c | 14 ++++++++------
>>> 1 file changed, 8 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>>> index 5ac312f..2e6c103 100644
>>> --- a/drivers/block/xen-blkfront.c
>>> +++ b/drivers/block/xen-blkfront.c
>>> @@ -582,12 +582,14 @@ static inline void flush_requests(struct
>>> blkfront_info *info)
>>> notify_remote_via_irq(info->irq);
>>> }
>>> -static inline bool blkif_request_flush_valid(struct request
>>> *req,
>>> - struct blkfront_info *info)
>>> +static inline bool blkif_request_flush_invalid(struct request *req,
>>> + struct blkfront_info *info)
>>> {
>>> return ((req->cmd_type != REQ_TYPE_FS) ||
>>> - ((req->cmd_flags & (REQ_FLUSH | REQ_FUA)) &&
>>> - !info->flush_op));
>>> + ((req->cmd_flags & REQ_FLUSH) &&
>>> + !(info->feature_flush & REQ_FLUSH)) ||
>>> + ((req->cmd_flags & REQ_FUA) &&
>>> + !(info->feature_flush & REQ_FUA)));
>
> Somewhat unrelated to the patch, but I am wondering whether we
> actually need flush_op field at all as it seems that it is
> unambiguously defined by REQ_FLUSH/REQ_FUA.
I was under an impression it was added for readability sake but we
definitely can remove it. If noone objects I'll send separate cleanup
patch (don't want to mix these two).
>
> -boris
>
>>> }
>>> /*
>>> @@ -612,8 +614,8 @@ static void do_blkif_request(struct request_queue *rq)
>>> blk_start_request(req);
>>> - if (blkif_request_flush_valid(req, info)) {
>>> - __blk_end_request_all(req, -EIO);
>>> + if (blkif_request_flush_invalid(req, info)) {
>>> + __blk_end_request_all(req, -EOPNOTSUPP);
>>> continue;
>>> }
>>>
>>>
>> Not sure if there has been some feedback yet (I can't see anything
>> threaded with this message in my inbox).
>>
>> FWIW I consulted "Documentation/block/writeback_cache_control.txt" for
>> this review. Apparently, REQ_FLUSH forces out "previously completed
>> write requests", whereas REQ_FUA delays the IO completion signal for
>> *this* request until "the data has been committed to non-volatile
>> storage". So, indeed, support for REQ_FLUSH only does not guarantee that
>> REQ_FUA can be served.
>>
>> Reviewed-by: Laszlo Ersek <ler...@redhat.com>
>>
>> Thanks
>> Laszlo
--
Vitaly
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
