Re: [dm-devel] [RFC PATCH v2 1/2] scsi: convert scsi_result_to_blk_status() to inline

From: Bart Van Assche <bvanassche@acm.org>
To: mwilck@suse.com, Mike Snitzer <snitzer@redhat.com>,
	Alasdair G Kergon <agk@redhat.com>,
	dm-devel@redhat.com, Hannes Reinecke <hare@suse.de>
Cc: Daniel Wagner <dwagner@suse.de>,
	linux-block@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [dm-devel] [RFC PATCH v2 1/2] scsi: convert scsi_result_to_blk_status() to inline
Date: Thu, 29 Apr 2021 09:20:24 -0700	[thread overview]
Message-ID: <08440651-6e8f-734a-ef43-561d9c2596a6@acm.org> (raw)
In-Reply-To: <20210429155024.4947-2-mwilck@suse.com>

On 4/29/21 8:50 AM, mwilck@suse.com wrote:
> This makes it possible to use scsi_result_to_blk_status() from
> code that shouldn't depend on scsi_mod (e.g. device mapper).

I think that's the wrong reason to make a function inline. Please
consider moving scsi_result_to_blk_status() into one of the block layer
source code files that already deals with SG I/O, e.g. block/scsi_ioctl.c.

> diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
> index 83f7e520be48..ba1e69d3bed9 100644
> --- a/include/scsi/scsi_cmnd.h
> +++ b/include/scsi/scsi_cmnd.h
> @@ -311,24 +311,44 @@ static inline struct scsi_data_buffer *scsi_prot(struct scsi_cmnd *cmd)
>  #define scsi_for_each_prot_sg(cmd, sg, nseg, __i)		\
>  	for_each_sg(scsi_prot_sglist(cmd), sg, nseg, __i)
>  
> +static inline void __set_status_byte(int *result, char status)
> +{
> +	*result = (*result & 0xffffff00) | status;
> +}
> +
>  static inline void set_status_byte(struct scsi_cmnd *cmd, char status)
>  {
> -	cmd->result = (cmd->result & 0xffffff00) | status;
> +	__set_status_byte(&cmd->result, status);
> +}
> +
> +static inline void __set_msg_byte(int *result, char status)
> +{
> +	*result = (*result & 0xffff00ff) | (status << 8);
>  }
>  
>  static inline void set_msg_byte(struct scsi_cmnd *cmd, char status)
>  {
> -	cmd->result = (cmd->result & 0xffff00ff) | (status << 8);
> +	__set_msg_byte(&cmd->result, status);
> +}
> +
> +static inline void __set_host_byte(int *result, char status)
> +{
> +	*result = (*result & 0xff00ffff) | (status << 16);
>  }
>  
>  static inline void set_host_byte(struct scsi_cmnd *cmd, char status)
>  {
> -	cmd->result = (cmd->result & 0xff00ffff) | (status << 16);
> +	__set_host_byte(&cmd->result, status);
> +}
> +
> +static inline void __set_driver_byte(int *result, char status)
> +{
> +	*result = (*result & 0x00ffffff) | (status << 24);
>  }
>  
>  static inline void set_driver_byte(struct scsi_cmnd *cmd, char status)
>  {
> -	cmd->result = (cmd->result & 0x00ffffff) | (status << 24);
> +	__set_driver_byte(&cmd->result, status);
>  }

The layout of the SCSI result won't change since it is used in multiple
UAPI data structures. I'd prefer to open-code host_byte() in
scsi_result_to_blk_status() instead of making the above changes.

Thanks,

Bart.