linux-kernel - Re: [PATCH] usb-storage: scsiglue: Changing the command result

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Message-ID: <CACVXFVPd9UQqMZFFsogMESzpDP=JVCpDJGWTAMrNHNazocJD4w@mail.gmail.com>
Date:	Tue, 15 Oct 2013 15:29:56 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Vishal Annapurve <vannapurve@...dia.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-usb <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] usb-storage: scsiglue: Changing the command result

On Thu, Sep 26, 2013 at 7:35 PM, Vishal Annapurve <vannapurve@...dia.com> wrote:
> Hi,
>
> There was a recent commit in mainline for the scsi devices which do not
> respond properly to medium access command:
>
> commit    18a4d0a22ed6c54b67af7718c305cd010f09ddf8
>
> [SCSI] Handle disk devices which can not process medium access commands
> We have experienced several devices which fail in a fashion we do not
> currently handle gracefully in SCSI. After a failure these devices will
> respond to the SCSI primary command set (INQUIRY, TEST UNIT READY, etc.)
> but any command accessing the storage medium will time out.
>
> I came across a USB drive which showed similar problem and what I see is
> usb storage is still not able to cope with such devices properly.
>
> The control flow downwards is like:
> scsi_times_out --> Setting cmd->result as DID_TIME_OUT
> scsi_error_handler
> scsi_unjam_host
> scsi_eh_abort_cmds
> command_abort    (sets US_FLIDX_TIMED_OUT for us->dflags
>                                   calls stop_transport,
>                                   and waits for)    usb_stor_control_thread
> (which is waiting for
>                                                                    transport
> call to return inside
>
> usb_stor_invoke_transport)
>                                                                    both
> usb_stor_control_thread and
>
> usb_stor_invoke_transport
>                                                     check for us->dflags
> timed_out bit and
>                                                      set the result as
> DID_ABORT
>                                                      and signal completion
> for command_abort
>                                                      to complete
> ......
> sd_eh_action
> checks for cmd->result and finds out that it's DID_ABORT rather than
> DID_TIME_OUT.
>
> This patch updates the command result to be TIME_OUT explicitly before
> returning from command_abort in scsiglue.c.
>
> I would like to know if this patch can work out for such USB Storage
> devices? What would be the better way to do the same?

Looks your diagnose is correct, and patch should be doable, the
only side effect is that previous returned DID_ABORT in srb->result
is replaced with DID_TIME_OUT now.

Another way is to implement .eh_timed_out callback to return different
error for the two failure, but looks not a big deal.

Thanks,
-- 
Ming Lei
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