On Tue, Feb 19 2008, Jens Axboe wrote:
> On Mon, Feb 18 2008, Andrew Morton wrote:
> > On Mon, 18 Feb 2008 19:16:30 +0100 Jens Axboe <[EMAIL PROTECTED]> wrote:
> >
> > > On Tue, Feb 12 2008, Andrew Morton wrote:
> > > > On Sat, 09 Feb 2008 08:30:40 -0500
> > > > Paul Clements <[EMAIL PROTECTED]> wrote:
> > > >
> > > > > + old_e = disk->queue->elevator;
> > > > > + if (elevator_init(disk->queue, "deadline") == 0 ||
> > > > > + elevator_init(disk->queue, "noop") == 0) {
> > > > > + elevator_exit(old_e);
> > > > > + }
> > > > > }
> > > >
> > > > afacit elevator_init() will not trigger a request_module(). And you
> > > > really
> > > > do want to trigger the request_module() here. Perhaps the block layer
> > > > should provide a means of doing so?
> > >
> > > Good point, I think elevator_get() should do that automatically. Does
> > > this look sane?
> > >
> > > diff --git a/block/elevator.c b/block/elevator.c
> > > index bafbae0..88318c3 100644
> > > --- a/block/elevator.c
> > > +++ b/block/elevator.c
> > > @@ -134,6 +134,21 @@ static struct elevator_type *elevator_get(const char
> > > *name)
> > > spin_lock(&elv_list_lock);
> > >
> > > e = elevator_find(name);
> > > + if (!e) {
> > > + char elv[ELV_NAME_MAX + strlen("-iosched")];
> > > +
> > > + spin_unlock(&elv_list_lock);
> > > +
> > > + if (!strcmp(name, "anticipatory"))
> > > + sprintf(elv, "as-iosched");
> > > + else
> > > + sprintf(elv, "%s-iosched", name);
> > > +
> > > + request_module(elv);
> > > + spin_lock(&elv_list_lock);
> > > + e = elevator_find(name);
> > > + }
> > > +
> > > if (e && !try_module_get(e->elevator_owner))
> > > e = NULL;
> >
> > Looks nice and simple. There might be some of the usual ordering problems
> > when this is called during boot, maybe is-initramfs-available-yet problems,
> > etc. But it's unlikely to make things regress from where they are now.
>
> Isn't request_module() and below robust enough to handle that?
BTW, I've verified that it works as expected (at least after boot):
carl:/sys/block/sda/queue # cat scheduler
noop [cfq]
carl:/sys/block/sda/queue # echo anticipatory > scheduler
carl:/sys/block/sda/queue # dmesg
[...]
io scheduler anticipatory registered
carl:/sys/block/sda/queue # cat scheduler
noop cfq [anticipatory]
So it properly loads as-iosched instead of failing, like it would have
done before and required the user to do a modprobe as-iosched first.
carl:/sys/block/sda/queue # echo foobar > scheduler
-bash: echo: write error: Invalid argument
carl:/sys/block/sda/queue # dmesg
[...]
elevator: type foobar not found
--
Jens Axboe
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