netdev - Re: [PATCH 1/2] Convert target drivers to use sbitmap

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Date:   Tue, 12 Jun 2018 11:08:43 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Bart Van Assche <Bart.VanAssche@....com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kent.overstreet@...il.com" <kent.overstreet@...il.com>,
        "linux1394-devel@...ts.sourceforge.net" 
        <linux1394-devel@...ts.sourceforge.net>,
        "jgross@...e.com" <jgross@...e.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "qla2xxx-upstream@...gic.com" <qla2xxx-upstream@...gic.com>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/2] Convert target drivers to use sbitmap

On Tue, Jun 12, 2018 at 04:32:03PM +0000, Bart Van Assche wrote:
> On Tue, 2018-06-12 at 09:15 -0700, Matthew Wilcox wrote:
> > On Tue, Jun 12, 2018 at 03:22:42PM +0000, Bart Van Assche wrote:
> > > Please introduce functions in the target core for allocating and freeing a tag
> > > instead of spreading the knowledge of how to allocate and free tags over all
> > > target drivers.
> > 
> > I can't without doing an unreasonably large amount of work on drivers that
> > I have no way to test.  Some of the drivers have the se_cmd already; some
> > of them don't.  I'd be happy to introduce a common function for freeing
> > a tag.
> 
> Which target drivers are you referring to? If you are referring to the sbp driver:
> I think that driver is dead and can be removed from the kernel tree. I even don't
> know whether that driver ever has had any users other than the developer of that
> driver.

For example tcm_fc:

        tag = sbitmap_queue_get(&se_sess->sess_tag_pool, &cpu);
        if (tag < 0)
                goto busy;

        cmd = &((struct ft_cmd *)se_sess->sess_cmd_map)[tag];

or qla2xxx:

        tag = sbitmap_queue_get(&se_sess->sess_tag_pool, &cpu);
        if (tag < 0)
                return NULL;

        cmd = &((struct qla_tgt_cmd *)se_sess->sess_cmd_map)[tag];

The core doesn't know at what offset from the pointer to store the tag
& cpu.  Only the individual drivers know their cmd layout.