Date: Mon, 16 Feb 2009 19:03:12 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: xcllnt@mac.com Cc: usb@freebsd.org Subject: Re: USB2+umass: root mount fails Message-ID: <20090216.190312.1756925299.imp@bsdimp.com> In-Reply-To: <6E9B5FF6-685B-427C-87A7-C95850DA5B6F@mac.com> References: <741FAA3B-B91A-4A23-B47F-21141A8D0B5D@mac.com> <20090216.173544.1555327603.imp@bsdimp.com> <6E9B5FF6-685B-427C-87A7-C95850DA5B6F@mac.com>
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In message: <6E9B5FF6-685B-427C-87A7-C95850DA5B6F@mac.com>
Marcel Moolenaar <xcllnt@mac.com> writes:
:
: On Feb 16, 2009, at 4:35 PM, M. Warner Losh wrote:
:
: > In message: <741FAA3B-B91A-4A23-B47F-21141A8D0B5D@mac.com>
: > Marcel Moolenaar <xcllnt@mac.com> writes:
: > :
: > : On Feb 16, 2009, at 3:13 PM, M. Warner Losh wrote:
: > :
: > : > In message: <ACB7DFF1-6C8E-4936-9BD9-BB2FD375F3BB@mac.com>
: > : > Marcel Moolenaar <xcllnt@mac.com> writes:
: > : > : Before I dig into the code, what's the current status of
: > : > : root mounts on USB mass storage devices?
: > : >
: > : > First, there's a kludge-o-round that is similar to your "sleep 10"
: > : > that you've added. It loops waiting for more devices to show up
: > if
: > : > the desired root file system hasn't appeared yet.
: > : >
: > : > There's no way for hot-plug busses to tell the kernel "I've
: > tried my
: > : > best to enumerate everything on my bus, and I'm done"
: > :
: > : Of course there is. Any and all USB hubs have a certain
: > : number of ports. You can trivially iterate over all of
: > : them and declare completion when you've tried them all.
: >
: > The hot-plug busses know. The mountroot code doesn't have a way to
: > wait for the hot-plug busses.
:
: Huh?
: root_mount_hold() and root_mount_rel() are specifically
: designed to inform the mountroot code that it needs to
: wait (or that it should go ahead and mount root).
r145250 | phk | 2005-04-18 15:21:26 -0600 (Mon, 18 Apr 2005) | 12 lines
Add a named reference-count KPI to hold off mounting of the root filesystem.
While we wait for holds to be released, print a list of who holds us
back once per second.
Use the new KPI from GEOM instead of vfs_mount.c calling g_waitidle().
Use the new KPI also from ata.
With ATAmkIII's newbusification, ata could narrowly miss the window
and ad0 would not exist when we tried to mount root.
----
But it looks like the old usb code didn't call it either... I think
old code enumerated right away during boot, while the new code defers
the enumeration until events can be processed...
Warner
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