2009/5/21 Kostik Belousov <kostikbel at gmail.com>:
> On Thu, May 21, 2009 at 09:23:15AM -0700, Scott Long wrote:
>> Kostik Belousov wrote:
>> >We do have the KPI for the callers that cannot drop the locks and need
>> >to do destroy_dev, destroy_dev_sched(9).
>>
>> Good to know, I'll look at destroy_dev_sched(). I'd rather not have to
>> roll my own decoupled version. And I understand the argument about
>> destroy_dev being a drain point for the API. However, what about
>> create_dev()? Making that non-blocking would help a lot.
>
> create_dev() can be made non-blocking, and this is the first argument pro
> Attilio patch.
>
> From the quick look, all that is needed is to replace M_WAITOK with
> M_NOWAIT inside prep_cdevsw() and devfs_alloc(). Untested patch below.
>
> diff --git a/sys/fs/devfs/devfs_devs.c b/sys/fs/devfs/devfs_devs.c
> index 4041911..f470ee8 100644
> --- a/sys/fs/devfs/devfs_devs.c
> +++ b/sys/fs/devfs/devfs_devs.c
> @@ -120,7 +120,7 @@ devfs_alloc(void)
> struct cdev *cdev;
> struct timespec ts;
>
> - cdp = malloc(sizeof *cdp, M_CDEVP, M_USE_RESERVE | M_ZERO | M_WAITOK);
> + cdp = malloc(sizeof *cdp, M_CDEVP, M_USE_RESERVE | M_ZERO | M_NOWAIT);
>
> cdp->cdp_dirents = &cdp->cdp_dirent0;
> cdp->cdp_dirent0 = NULL;
> diff --git a/sys/kern/kern_conf.c b/sys/kern/kern_conf.c
> index 284f482..acdd44a 100644
> --- a/sys/kern/kern_conf.c
> +++ b/sys/kern/kern_conf.c
> @@ -559,7 +559,7 @@ prep_cdevsw(struct cdevsw *devsw)
> return;
> if (devsw->d_flags & D_NEEDGIANT) {
> dev_unlock();
> - dsw2 = malloc(sizeof *dsw2, M_DEVT, M_WAITOK);
> + dsw2 = malloc(sizeof *dsw2, M_DEVT, M_NOWAIT);
> dev_lock();
> } else
> dsw2 = NULL;
You need to check return values here if it returns NULL.
IMHO, having a non-sleepable version of destroy_dev(), create_dev()
and such would be ideal.
Ideally, we should resolve all the sleeping point and do the conversion.
I'm unable to check the code right now.
Thanks,
Attilio
--
Peace can only be achieved by understanding - A. Einstein