[PATCH/RFC] Allowing REQ_FAILFAST to be set from SG_IO

[PATCH/RFC] Allowing REQ_FAILFAST to be set from SG_IO

[Hannes Reinecke]

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Hi all,

this patch allows to set the REQ_FAILFAST flag to be set from SG_IO
commands. With it one can send generic SCSI commands which behave
exactly like normal requests send via the block layer.

Comments etc welcome.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke			hare@suse.de
SuSE Linux Products GmbH		S390 & zSeries
Maxfeldstraße 5				+49 911 74053 688
90409 Nürnberg				http://www.suse.de

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Allow FAILFAST flag to be set for SG_IO commands

This patch allows the FAILFAST flag to be set for SG_IO commands.

Signed-off-by: Hannes Reinecke <hare@suse.de>

diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
index b33eda2..658b1b5 100644
--- a/block/scsi_ioctl.c
+++ b/block/scsi_ioctl.c
@@ -295,6 +295,8 @@ static int sg_io(struct file *file, requ
 	rq->sense_len = 0;
 
 	rq->flags |= REQ_BLOCK_PC;
+	if (hdr->flags & SG_FLAGS_FAILFAST)
+		rq->flags |= REQ_FAILFAST;
 	bio = rq->bio;
 
 	/*
diff --git a/include/scsi/sg.h b/include/scsi/sg.h
index 0a487fe..9cc466a 100644
--- a/include/scsi/sg.h
+++ b/include/scsi/sg.h
@@ -142,6 +142,7 @@ typedef struct sg_io_hdr
 #define SG_FLAG_UNUSED_LUN_INHIBIT 2   /* default is overwrite lun in SCSI */
 				/* command block (when <= SCSI_2) */
 #define SG_FLAG_MMAP_IO 4       /* request memory mapped IO */
+#define SG_FLAG_FAILFAST 8      /* request should set FAILFAST flag */
 #define SG_FLAG_NO_DXFER 0x10000 /* no transfer of kernel buffers to/from */
 				/* user space (debug indirect IO) */
 

Re: [PATCH/RFC] Allowing REQ_FAILFAST to be set from SG_IO

[Douglas Gilbert]

Hannes Reinecke wrote:
> Hi all,
> 
> this patch allows to set the REQ_FAILFAST flag to be set from SG_IO
> commands. With it one can send generic SCSI commands which behave
> exactly like normal requests send via the block layer.
> 
> Comments etc welcome.

Hannes,
Looks good. There is no proposed change to sg.c .
Could SG_FLAG_FAILFAST be made to work via sg device
nodes?

Doug Gilbert


> ------------------------------------------------------------------------
> 
> Allow FAILFAST flag to be set for SG_IO commands
> 
> This patch allows the FAILFAST flag to be set for SG_IO commands.
> 
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> 
> diff --git a/block/scsi_ioctl.c b/block/scsi_ioctl.c
> index b33eda2..658b1b5 100644
> --- a/block/scsi_ioctl.c
> +++ b/block/scsi_ioctl.c
> @@ -295,6 +295,8 @@ static int sg_io(struct file *file, requ
>  	rq->sense_len = 0;
>  
>  	rq->flags |= REQ_BLOCK_PC;
> +	if (hdr->flags & SG_FLAGS_FAILFAST)
> +		rq->flags |= REQ_FAILFAST;
>  	bio = rq->bio;
>  
>  	/*
> diff --git a/include/scsi/sg.h b/include/scsi/sg.h
> index 0a487fe..9cc466a 100644
> --- a/include/scsi/sg.h
> +++ b/include/scsi/sg.h
> @@ -142,6 +142,7 @@ typedef struct sg_io_hdr
>  #define SG_FLAG_UNUSED_LUN_INHIBIT 2   /* default is overwrite lun in SCSI */
>  				/* command block (when <= SCSI_2) */
>  #define SG_FLAG_MMAP_IO 4       /* request memory mapped IO */
> +#define SG_FLAG_FAILFAST 8      /* request should set FAILFAST flag */
>  #define SG_FLAG_NO_DXFER 0x10000 /* no transfer of kernel buffers to/from */
>  				/* user space (debug indirect IO) */
>  

Re: [PATCH/RFC] Allowing REQ_FAILFAST to be set from SG_IO

[James Bottomley]

On Wed, 2006-05-10 at 12:41 -0400, Douglas Gilbert wrote:
> Looks good. There is no proposed change to sg.c .
> Could SG_FLAG_FAILFAST be made to work via sg device
> nodes?

Rather than having to maintain two separate paths for SG_IO and hence
keep running into this issue, what will it take for sg to use the block
scsi_ioctl.c?

James

Re: [PATCH/RFC] Allowing REQ_FAILFAST to be set from SG_IO

[Douglas Gilbert]

James Bottomley wrote:
> On Wed, 2006-05-10 at 12:41 -0400, Douglas Gilbert wrote:
> 
>>Looks good. There is no proposed change to sg.c .
>>Could SG_FLAG_FAILFAST be made to work via sg device
>>nodes?
> 
> 
> Rather than having to maintain two separate paths for SG_IO and hence
> keep running into this issue, what will it take for sg to use the block
> scsi_ioctl.c?

Methinks a large amount of code and a lot of testing.
Hannes is proposing a new SG_FLAG value that would
only be active in the block layer SG_IO. The existing
SG_FLAG values are only implemented by the sg driver.
Around that level in the sg driver, the command
injection and response processing are asynchronous
and that can be exposed to the sg user. The block
SG_IO is synchronous with no easy way to break
it down to its component parts.

On further thought if anything in the scsi midlayer
(or the block layer) is slowing down an error report
getting back to a sg user then that is most likely a
bug. The sg driver sends commands with retries set to
zero. Also settings in the read/write error recovery
mode page can effect how long a disk (or cd/drive)
spends trying to recovery from errors (and
SG_FLAG_FASTFAIL has no effect at the device (lu)
end).

Doug Gilbert

Re: [PATCH/RFC] Allowing REQ_FAILFAST to be set from SG_IO

[Hannes Reinecke]

Douglas Gilbert wrote:
> James Bottomley wrote:
>> On Wed, 2006-05-10 at 12:41 -0400, Douglas Gilbert wrote:
>>
>>> Looks good. There is no proposed change to sg.c .
>>> Could SG_FLAG_FAILFAST be made to work via sg device
>>> nodes?
>>
>> Rather than having to maintain two separate paths for SG_IO and hence
>> keep running into this issue, what will it take for sg to use the block
>> scsi_ioctl.c?
> 
> Methinks a large amount of code and a lot of testing.
> Hannes is proposing a new SG_FLAG value that would
> only be active in the block layer SG_IO. The existing
> SG_FLAG values are only implemented by the sg driver.
> Around that level in the sg driver, the command
> injection and response processing are asynchronous
> and that can be exposed to the sg user. The block
> SG_IO is synchronous with no easy way to break
> it down to its component parts.
> 
> On further thought if anything in the scsi midlayer
> (or the block layer) is slowing down an error report
> getting back to a sg user then that is most likely a
> bug. The sg driver sends commands with retries set to
> zero. Also settings in the read/write error recovery
> mode page can effect how long a disk (or cd/drive)
> spends trying to recovery from errors (and
> SG_FLAG_FASTFAIL has no effect at the device (lu)
> end).
That doesn't apply here. The error recovery in scsi_unjam_host() will be
triggered regardless of the retry setting. Setting the retry to zero
will only cause the command _not_ to be retried; if the device still
reports an error condition the error handler will still be invoked.

One might argue that no error recovery is required for sg.c commands as
the user will have full control (up to and including bus / device reset)
so he's responsible to implement his own error recovery. In that case we
should always send command from sg.c down with the failfast flag set.

But that's a different discussion.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke			hare@suse.de
SuSE Linux Products GmbH		S390 & zSeries
Maxfeldstraße 5				+49 911 74053 688
90409 Nürnberg				http://www.suse.de
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Re: [PATCH/RFC] Allowing REQ_FAILFAST to be set from SG_IO

[Jens Axboe]

On Wed, May 10 2006, James Bottomley wrote:
> On Wed, 2006-05-10 at 12:41 -0400, Douglas Gilbert wrote:
> > Looks good. There is no proposed change to sg.c .
> > Could SG_FLAG_FAILFAST be made to work via sg device
> > nodes?
> 
> Rather than having to maintain two separate paths for SG_IO and hence
> keep running into this issue, what will it take for sg to use the block
> scsi_ioctl.c?

The plan still remains to use bsg to consolidate the two.

-- 
Jens Axboe

Re: [PATCH/RFC] Allowing REQ_FAILFAST to be set from SG_IO

[Hannes Reinecke]

Douglas Gilbert wrote:
> Hannes Reinecke wrote:
>> Hi all,
>>
>> this patch allows to set the REQ_FAILFAST flag to be set from SG_IO
>> commands. With it one can send generic SCSI commands which behave
>> exactly like normal requests send via the block layer.
>>
>> Comments etc welcome.
> 
> Hannes,
> Looks good. There is no proposed change to sg.c .
> Could SG_FLAG_FAILFAST be made to work via sg device
> nodes?
> 
That will be tricky. sg.c is using scsi_execute_async() which doesn't
provide for any flags to be passed.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke			hare@suse.de
SuSE Linux Products GmbH		S390 & zSeries
Maxfeldstraße 5				+49 911 74053 688
90409 Nürnberg				http://www.suse.de
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To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
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