netdev - Re: [PATCH 1/5] initdev:kernel: Asynchronously-discovered device synchronization, v5

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Date:	Tue, 5 May 2009 23:53:38 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	David VomLehn <dvomlehn@...co.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	linux-usb@...r.kernel.org, greg@...ah.com,
	linux-scsi@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/5] initdev:kernel: Asynchronously-discovered device 
	synchronization, v5

2009/5/5 Ming Lei <tom.leiming@...il.com>:
> On Mon, 4 May 2009 11:07:52 -0400 (EDT)
> Alan Stern <stern@...land.harvard.edu> wrote:
>
>> On Mon, 4 May 2009, Arjan van de Ven wrote:
>>
>> > > > for normal device probing we already have infrastructure
>> > > > though... wait_for_device_probe, driver_probe_done and
>> > > > friends... (the scsi scanning thread is being converted to the
>> > > > async infrastructure btw)
>> > > >
>> > > > do we need to invent more ?
>> > >
>> > > I suppose the usb-storage scanning thread could also be converted
>> > > to the async infrastructure, although I haven't heard of anybody
>> > > working on it.
>> > >
>> > > But the USB hub driver's thread (khubd) cannot be converted.  It
>> > > is central to the discovery of USB-based block devices.  How
>> > > would you handle that?
>> >
>> > take a ref in the driver_probe_done() sense, and release it when you
>> > know you're done probing....
>> >
>> > at that point all existing infrastructure will just work.
>>
>> Isn't there still something missing?  The wait_for_device_probe()
>> routine would wait until all attached devices had been probed.  But
>> why should prepare_namespace() have to wait that long?  Wouldn't it be
>> better to wait only until the root device has been registered?
>
> Yes, maybe David should merge the following patch into the patch
> No.5(initdev:kernel: USB and SCSI block init device notification, v3).
>
> Right?

Also need all block device drivers use initdev_*, much work to do,:-)

>
> diff --git a/init/do_mounts.c b/init/do_mounts.c
> index dd7ee5f..22fd773 100644
> --- a/init/do_mounts.c
> +++ b/init/do_mounts.c
> @@ -358,6 +358,12 @@ void __init mount_root(void)
>  #endif
>  }
>
> +static int root_dev_done()
> +{
> +       return !!(ROOT_DEV = name_to_dev_t(saved_root_name));
> +}
> +
> +
>  /*
>  * Prepare the namespace - decide what/where to mount, load ramdisks,
> etc. */
> @@ -398,12 +404,12 @@ void __init prepare_namespace(void)
>                goto out;
>
>        /* wait for any asynchronous scanning to complete */
> -       if ((ROOT_DEV == 0) && root_wait) {
> +       if (ROOT_DEV == 0 && root_wait) {
>                printk(KERN_INFO "Waiting for root device %s...\n",
>                        saved_root_name);
> -               while (driver_probe_done() != 0 ||
> -                       (ROOT_DEV = name_to_dev_t(saved_root_name)) ==
> 0)
> -                       msleep(100);
> +               do {
> +                       initdev_wait(BOOTDEV_BLOCK, root_dev_done);
> +               } while (!ROOT_DEV);
>                async_synchronize_full();
>        }
>
>
>
>
> --
> Lei Ming
>



-- 
Lei Ming
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