Re: [PATCH] scsi: Change the return type of the .queuecommand() callback

[Bart Van Assche <bvanassche@acm.org>]

On 1/7/26 5:36 AM, James Bottomley wrote:
> On Tue, 2026-01-06 at 11:52 -0700, Bart Van Assche wrote:
>> Let the compiler verify whether a valid value is returned by the
>> .queuecommand() implementations by changing their return type from
>> 'int' into 'enum scsi_qc_status'.
> 
> What makes you think the C compiler checks enum values?  Traditionally
> the opposite has been true: enum is just a fancy #define, which is how
> we use it in a lot of the kernel code.  Even if the compiler people
> came up with a switch to turn on this behaviour, we'd likely have
> trouble turning it on without eliminating all the fancy #define use.

If I revert commit e414748b7e83 ("scsi: aacraid: Improve code 
readability") and build the kernel with the git HEAD of clang with this
patch applied then following error message appears:

drivers/scsi/aacraid/linit.c:245:29: error: implicit conversion from 
enumeration
       type 'enum scsi_disposition' to different enumeration type
       'enum scsi_qc_status' [-Werror,-Wimplicit-enum-enum-cast]
   245 |         return aac_scsi_cmd(cmd) ? FAILED : 0;
       |         ~~~~~~                     ^~~~~~

This patch also helps those who build the kernel with gcc because the
zero-day infrastructure builds the kernel with both gcc and clang and
hence will spot it if an incorrect value is returned from a queuecommand
function.

I will improve the patch description when I repost this patch and will
change "compiler" into "clang 21.1 or later".

Thanks,

Bart.