On Thu, Apr 24, 2008 at 03:56:04PM -0700, Greg KH wrote: > On Fri, Apr 25, 2008 at 12:25:04AM +0300, Pekka J Enberg wrote: > > On Thu, 24 Apr 2008, Pekka J Enberg wrote: > > > > From: Pekka Enberg <penberg@xxxxxxxxxxxxxx> > > > > > > > > Add a new kernel config option CONFIG_LATE_ROOT_MOUNT that makes the kernel > > > > wait until background scanning of USB mass storage devices is complete before > > > > attempting to mount the root filesystem. > > > > > > > > The config option is an alternative to the root_delay= kernel parameter > > > > solution people currently use to boot from USB mass storage devices. > > > > On Thu, 24 Apr 2008, Alan Stern wrote: > > > This doesn't take into account what happens when CONFIG_SCSI_SCAN_ASYNC > > > is set. > > > > Oh, right. Thanks! So something like the following should take care of it. > > > > Pekka > > > > Subject: [RFC/PATCH] usb-storage: wait for device scanning before mounting root V2 > > From: Pekka Enberg <penberg@xxxxxxxxxxxxxx> > > > > Add a new kernel config option CONFIG_LATE_ROOT_MOUNT that makes the kernel > > wait until background scanning of USB mass storage devices is complete before > > attempting to mount the root filesystem. > > What happens if there is no USB device present in the system? Because > of that, there is no way that this option could ever be enabled by any > distro or anyone wanting their kernel to run on more than one machine :( > > I don't like it. This also has all sorts of races between do_mounts 'waiting' and the actual USB device enumeration. It's entirely possible that the kernel loads via BIOS, the USB drivers are loaded, that forces devices to disconnect/reset, and they take a while to re-enumerate. During that delay, the kernel gets to do_mount; now, no devices show in this "waiting for scan" count. The right way to do this is via initrd and something like devlabel to wait for a specific device to appear. On some systems, you may want to wait for several devices to appear. I don't like this either. Matt -- Matthew Dharm Home: mdharm-usb@xxxxxxxxxxxxxxxxxx Maintainer, Linux USB Mass Storage Driver What, are you one of those Microsoft-bashing Linux freaks? -- Customer to Greg User Friendly, 2/10/1999
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