Re: [PATCH] scsi: core: Log SCSI command age with errors

[Laurence Oberman <loberman@redhat.com>]

On Mon, 2019-09-23 at 11:31 +0530, Milan P. Gandhi wrote:
> Couple of users had requested to print the SCSI command age along 
> with command failure errors. This is a small change, but allows 
> users to get more important information about the command that was 
> failed, it would help the users in debugging the command failures:
> 
> Signed-off-by: Milan P. Gandhi <mgandhi@redhat.com>
> ---
> diff --git a/drivers/scsi/scsi_logging.c
> b/drivers/scsi/scsi_logging.c
> index ecc5918e372a..ca2182bc53c6 100644
> --- a/drivers/scsi/scsi_logging.c
> +++ b/drivers/scsi/scsi_logging.c
> @@ -437,6 +437,7 @@ void scsi_print_result(const struct scsi_cmnd
> *cmd, const char *msg,
>  	const char *mlret_string = scsi_mlreturn_string(disposition);
>  	const char *hb_string = scsi_hostbyte_string(cmd->result);
>  	const char *db_string = scsi_driverbyte_string(cmd->result);
> +	unsigned long cmd_age = (jiffies - cmd->jiffies_at_alloc) / HZ;
>  
>  	logbuf = scsi_log_reserve_buffer(&logbuf_len);
>  	if (!logbuf)
> @@ -478,10 +479,15 @@ void scsi_print_result(const struct scsi_cmnd
> *cmd, const char *msg,
>  
>  	if (db_string)
>  		off += scnprintf(logbuf + off, logbuf_len - off,
> -				 "driverbyte=%s", db_string);
> +				 "driverbyte=%s ", db_string);
>  	else
>  		off += scnprintf(logbuf + off, logbuf_len - off,
> -				 "driverbyte=0x%02x", driver_byte(cmd-
> >result));
> +				 "driverbyte=0x%02x ",
> +				 driver_byte(cmd->result));
> +
> +	off += scnprintf(logbuf + off, logbuf_len - off,
> +			 "cmd-age=%lus", cmd_age);
> +
>  out_printk:
>  	dev_printk(KERN_INFO, &cmd->device->sdev_gendev, "%s", logbuf);
>  	scsi_log_release_buffer(logbuf);
> 

This looks to be a useful debug addition to me, and the code looks
correct.
I believe this has also been tested by Milan in our lab.

Reviewed-by: Laurence Oberman <loberman@redhat.com>