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SubjectRe: [PATCH] xen/blkfront: improve protection against issuing unsupported REQ_FUA
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 <vkuznets@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.

-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 <lersek@redhat.com>
>
> Thanks
> Laszlo



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