On Fri, Jul 21, 2023 at 09:01:32AM -0700, Bart Van Assche wrote:
> Because scsi_finish_command() subtracts the residual from the buffer
> length, residual overflows must not be reported. Reflect this in the
> SCSI documentation. See also commit 9237f04e12cc ("scsi: core: Fix
> scsi_get/set_resid() interface")
>
> Cc: Damien Le Moal <dlemoal@xxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxx>
> Cc: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> Documentation/scsi/scsi_mid_low_api.rst | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/scsi/scsi_mid_low_api.rst b/Documentation/scsi/scsi_mid_low_api.rst
> index 6fa3a6279501..022198c51350 100644
> --- a/Documentation/scsi/scsi_mid_low_api.rst
> +++ b/Documentation/scsi/scsi_mid_low_api.rst
> @@ -1190,11 +1190,11 @@ Members of interest:
> - pointer to scsi_device object that this command is
> associated with.
> resid
> - - an LLD should set this signed integer to the requested
> + - an LLD should set this unsigned integer to the requested
> transfer length (i.e. 'request_bufflen') less the number
> of bytes that are actually transferred. 'resid' is
> preset to 0 so an LLD can ignore it if it cannot detect
> - underruns (overruns should be rare). If possible an LLD
> + underruns (overruns should not be reported). An LLD
I'm very late to party, sorry. But we have certainly seen at least one
overrun reported some years ago on a FC SAN. We've changed some handling
in zFCP due to that (
a099b7b1fc1f ("scsi: zfcp: add handling for FCP_RESID_OVER to the fcp ingress path")
). The theory back than was, that it was cause by either a faulty ISL in
the fabric, or some other "bit-errors" on the wire that caused some FC
frames being dropped during transmit.
I added that we mark such commands with `DID_ERROR`, so they are
retried, if that is permissible.
> should set 'resid' prior to invoking 'done'. The most
> interesting case is data transfers from a SCSI target
> device (e.g. READs) that underrun.
--
Best Regards, Benjamin Block / Linux on IBM Z Kernel Development
IBM Deutschland Research & Development GmbH / https://www.ibm.com/privacy
Vors. Aufs.-R.: Gregor Pillen / Geschäftsführung: David Faller
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