Re: [GIT PULL] SCSI queuecommand API change for 2.6.37-rc1

Linus Torvalds
2010-11-13T04:43:43Z

On Fri, Nov 12, 2010 at 8:28 PM, Matthew Wilcox <matthew@wil.cx> wrote:
> Actually, it'd be even better if we took away an argument.
>
> int queuecommand(struct scsi_cmnd *cmd);
>
> Every single driver sets cmd->scsi_done = done;

.. and i that's all they really ever do with it, I guess that that
would indeed be an improvement.

I still do think that passing in shost is actually a good idea, since
you'll normally be needing it for locking and other things anyway
(looking at the libata-scsi.c one, for example, the very first thing
it wants to do is to look up the port from the shost pointer).

Having to inevitably do that silly double dereference
("cmd->device->host") seems bogus. Passing in the host you want to
queue something on seems to be natural, and avoids that nasty chain of
dereferences, so it really should improve the code.

I don't think there are any drivers that don't want that host pointer
pretty much immediately, even if they can elide the locking. But I
admit I only looked at two (qla4xxx driver does the exact same thing:
the very first thing in the queuecommand function is
"to_qla_host(cmd->device->host)", but it wants that hostdata thing
too, so whatever.)

So the shost pointer is certainly a lot more useful than the 'done'
function pointer. So yeah, I'd switch them around - pass the 'done'
thing indirectly, and the shost directly.

Linus