Re: current linus bk, error mounting root

[Kyle Moffett]

On Mar 21, 2005, at 19:19, Andrew Morton wrote:
> Jon Smirl <jonsmirl@xxxxxxxxx> wrote:
> > Jens is right that this is a user space issue, but how many people are
> > going to find this out the hard way when their root drives stop
> > mounting. Since no one is complaining I have to assume that most
> > kernel developers have their root device drivers built into the
> > kernel. I was loading mine as a module since for a long time Redhat
> > was not shipping kernels with SATA built in.
>
> I don't agree that this is a userspace issue.  It's just not sane for a
> driver to be in an unusable state for an arbitrary length of time after
> modprobe returns.

What about if I'm booting from a USB drive?  In that case, because of 
the
asynchrony of USB probing, it may take 1 or 2 seconds for my attached 
hub
to power on, wake up, boot its embedded microprocessor, etc before it 
will
respond to signals.  In such a case, as far as the root hub can tell,
there are _no_ external devices for a couple seconds, and that's 
ignoring
that my external USB bootdrive may _also_ need time to "boot" before it
will be accessible, and that's only once its parent hub has become
available.

I think that the kernel needs some kind of wait-for-device API that is
accessible from kernel-space for the simple boot sequence, perhaps just
waiting for a specific kobject to be detected and complete 
initialization.

For an initrd/initramfs in userspace, dnotify on sysfs (For the static
/dev case), or dnotify on /dev (For the udev case) should allow it to
detect when the device is available.

Cheers,
Kyle Moffett

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