Re: [PATCH] scsi: use set_host_byte instead of open-coding it

[Steffen Maier <maier@linux.vnet.ibm.com>]

On 10/10/2017 05:29 PM, Johannes Thumshirn wrote:
> Call set_host_byte() instead of open-coding it.
> 
> Converted using this simple Coccinelle spatch
> 
> <SmPL>
> @@
> local idexpression struct scsi_cmnd *c;
> expression E1;
> @@
> 
> - c->result = E1 << 16;
> + set_host_byte(c, E1);

Maybe I misunderstand, but doesn't set_host_byte only set the host byte 
but leave the other 3 parts untouched in c->result?

static inline void set_host_byte(struct scsi_cmnd *cmd, char status)
{
	cmd->result = (cmd->result & 0xff00ffff) | (status << 16);
}

In contrast, assigning something to c->result resets all parts.
If so, the semantic patch would introduce a subtle semantic change.
Unless it's guaranteed that in all the touched cases, c->result always 
has 0 for status, message, and driver byte before calling set_host_byte().

Bart's suggestion also sounds nice.

FYI: Originally, I only thought about using set_host_byte in that one 
place fix of yours; I did not expect a full framework rework.

-- 
Mit freundlichen Grüßen / Kind regards
Steffen Maier

Linux on z Systems Development

IBM Deutschland Research & Development GmbH
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschaeftsfuehrung: Dirk Wittkopp
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294