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

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Message-ID: <20171011132552.tqfrg6ccqny2bzn2@linux-x5ow.site>
Date:   Wed, 11 Oct 2017 15:25:52 +0200
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     Steffen Maier <maier@...ux.vnet.ibm.com>
Cc:     "Martin K . Petersen" <martin.petersen@...cle.com>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Linux SCSI Mailinglist <linux-scsi@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>,
        Bart Van Assche <Bart.VanAssche@...disk.com>,
        Oliver Neukum <oneukum@...e.com>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH] scsi: use set_host_byte instead of open-coding it

On Wed, Oct 11, 2017 at 03:05:40PM +0200, Steffen Maier wrote:
> 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().

Yes it does, another case I'll have to add to my coccinelle spatch, thanks for
reminding me (and I'm also doing it for set_msg_byte() and set_driver_byte(),
the status byte will be done manually probably).

> 
> Bart's suggestion also sounds nice.

Yes I'm working on implementing it currently.

> 
> 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.

Oh well:
$ git diff --stat master..
[..]
 80 files changed, 589 insertions(+), 540 deletions(-)

Byte,
	Johannes

-- 
Johannes Thumshirn                                          Storage
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