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

Ming Lei
2009-05-05T15:47:39Z

On Mon, 4 May 2009 11:07:52 -0400 (EDT)
Alan Stern <stern@rowland.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?

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