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

[Martin Wilck <mwilck@suse.com>]

Hi Bart,

thanks for looking at this.

On Thu, 2021-04-29 at 09:20 -0700, Bart Van Assche wrote:
> 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.

scsi_ioctl.c, are you certain? scsi_result_to_blk_status() is an
important part of the block/scsi interface... You're right that that
this function is not a prime candidate for inlining, but I'm still
wondering where it belongs if we don't.

Looking forward to see what others think.

> 
> > 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.

OK. I'm generally no fan of hard-coding but I guess you're right
in this case.

Thanks,
Martin