From: "Chun Yan Liu" <cyliu@suse.com>
To: George Dunlap <george.dunlap@eu.citrix.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
Juergen Gross <JGross@suse.com>
Cc: Jim Fehlig <JFEHLIG@suse.com>, Simon Cao <caobosimon@gmail.com>,
Wei Liu <wei.liu2@citrix.com>,
Ian Campbell <ian.campbell@citrix.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: [PATCH V4 3/7] libxl: add pvusb API [and 1 more messages]
Date: Thu, 18 Jun 2015 00:24:36 -0600 [thread overview]
Message-ID: <5582D4A402000066000D885D@relay2.provo.novell.com> (raw)
In-Reply-To: <55814B9F.6070909@eu.citrix.com>
>>> On 6/17/2015 at 06:27 PM, in message <55814B9F.6070909@eu.citrix.com>, George
Dunlap <george.dunlap@eu.citrix.com> wrote:
> On 06/17/2015 04:59 AM, Juergen Gross wrote:
> > On 06/16/2015 06:34 PM, George Dunlap wrote:
> >> On Tue, Jun 16, 2015 at 4:59 PM, Ian Jackson
> >> <Ian.Jackson@eu.citrix.com> wrote:
> >>> George Dunlap writes ("Re: [Xen-devel] [PATCH V4 3/7] libxl: add
> >>> pvusb API [and 1 more messages]"):
> >>>>> Yes. The whole point of paths like this is that they are stable if
> >>>>> the physical topology doesn't change. So on my netbook
> >>>>>
> >>>>> /dev/disk/by-path/pci-0000:00:1d.7-usb-0:1:1.0-scsi-0:0:0:0-part1
> >>>>>
> >>>>> always refers to the 1st MBR partition on logical device 0 on the USB
> >>>>> storage device plugged into the USB port physically on the front left
> >>>>> of the computer.
> >>>>
> >>>> That would be great if it were true, but I'm not convinced that the
> >>>> above path doesn't include a globally-enumerated bus number, which
> >>>> might
> >>>> change across reboots if it's enumerated in a different order.
> >>>>
> >>>> It may be that the format above is *not* based on the sysfs path of the
> >>>> device; that the '0' immediately after the USB means "the first (and
> >>>> perhaps only) controller at this PCI address". In which case, yes,
> >>>> having a string like this might be a unique identifier for a particular
> >>>> port that would be stable across reboots. That needs some
> >>>> investigation.
> >>>
> >>> That does seem to be the case:
> >>
> >> What seems to be the case -- that it contains the global bus, or not?
> >>
> >>> Looking at the output of udevadm monitor --property for sdc1 (on
> >>> another plug):
> >>>
> >>>
> DEVPATH=/devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1:1.0/host22/target22:0:0
> /22:0:0:0/block/sdc/sdc1
> >>>
> >>> ID_PATH=pci-0000:00:1d.7-usb-0:1:1.0-scsi-0:0:0:0
> >>> ID_PATH_TAG=pci-0000_00_1d_7-usb-0_1_1_0-scsi-0_0_0_0
> >>>
> >>> I don't know where that ID_PATH comes from.
> >>
> >> It looks like that's constructed in udev:
> >>
> >>
> http://cgit.freedesktop.org/systemd/systemd/tree/src/udev/udev-builtin-path_i
> d.c
> >>
> >>
> >> See handle_usb() (line 542) in particular.
> >>
> >> If I'm reading it right, what it basically does it take the
> >> [bus]-[port], and replace it with usb-0:[port]. (IOW, the '0' is
> >> hard-coded.)
> >>
> >> Also, if I'm reading it right, this won't work properly for Juergen's
> >> system that has two USB devices at the same pci address -- they'll
> >> both end up resolving to [pciaddr]-usb-0:[whatever].
> >>
> >> Juergen -- can you give this a try? Run "udevadm info" on the two USB
> >> busses that share the same PCI slot, and see if the ID_PATH is the
> >> same for both?
> >
> > This was the correct question. :-)
> >
> > The ID_PATH is the same, but:
> >
> > It turns out that the two busses are for one physical hcd. One is the
> > bus for USB 3.0, the other one for USB 2.0. I guess the bus is just
> > selected by the capability of the plugged in device.
> >
> > So the [port] in "usb-0:[port]" is unique across the two logical
> > busses.
>
> Right -- I think I had come to the conclusion that would probably be the
> case later yesterday evening. Glad to have it confirmed.
>
> So in addition to our other identifiers, stealing udev's naming scheme
> should work, and would be useful.
>
> The next challenge would be how to implement it effectively. It's
> already udev's job to make sure that a string is unique -- as much as
> possible we want to leverage their efforts, rather than re-implementing
> our own.
>
> One thing that Ian suggested was that we could add a udev rule that
> would create links from the ID_PATH of the usb device into the sysfs
> device node. (Both seem to be available in the udev rule environment.)
> That would allow us to easily translate the ID_PATH into the other
> things we might want (bus-port, bus.addr, &c) and vice versa.
>
> But I think all that will certainly not be done by the feature freeze.
>
> The core functionality of Chunyan's series, wrt the pvusb functionality
> is complete; as with my HVM series before, it's mainly the interface
> that is being discussed.
>
> There are two options here: Chunyan could try to implement the interface
> we've been discussing here (assuming that she doesn't have any
> objections to what we've described);
No, I don't have any objections. I can do that.
- Chunyan
> or, I could take Chunyan's series,
> try to implement what we've been talking about, and then add in the HVM
> functionality as well.
>
> What does everyone think?
>
> -George
>
>
>
>
next prev parent reply other threads:[~2015-06-18 6:24 UTC|newest]
Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-10 3:20 [PATCH V4 0/7] xen pvusb toolstack work Chunyan Liu
2015-06-10 3:20 ` [PATCH V4 1/7] libxl: export some functions for pvusb use Chunyan Liu
2015-06-11 16:08 ` Ian Jackson
2015-06-11 16:28 ` Wei Liu
2015-06-12 15:14 ` Ian Jackson
2015-06-10 3:20 ` [PATCH V4 2/7] libxl_read_file_contents: add new entry to read sysfs file Chunyan Liu
2015-06-11 16:16 ` Ian Jackson
2015-06-12 7:00 ` Chun Yan Liu
2015-06-12 15:11 ` Ian Jackson
2015-06-10 3:20 ` [PATCH V4 3/7] libxl: add pvusb API Chunyan Liu
2015-06-11 15:00 ` Juergen Gross
2015-06-11 16:07 ` Ian Jackson
2015-06-11 16:42 ` Ian Jackson
2015-06-12 7:39 ` Chun Yan Liu
2015-06-12 8:06 ` Chun Yan Liu
2015-06-12 11:22 ` Ian Jackson
2015-06-15 14:17 ` George Dunlap
2015-06-15 14:25 ` Jürgen Groß
2015-06-15 14:34 ` George Dunlap
2015-06-15 18:26 ` Juergen Gross
2015-06-16 10:30 ` George Dunlap
2015-06-16 10:51 ` Juergen Gross
2015-06-16 11:11 ` George Dunlap
2015-06-16 11:19 ` Juergen Gross
2015-06-16 11:23 ` George Dunlap
2015-06-16 11:44 ` Ian Jackson
2015-06-17 11:24 ` Ian Campbell
2015-06-18 11:50 ` George Dunlap
2015-06-18 12:08 ` George Dunlap
2015-06-18 13:03 ` Juergen Gross
2015-06-22 13:29 ` Proposed plan for libxl USB interface (was Re: [PATCH V4 3/7] libxl: add pvusb API) George Dunlap
2015-06-22 14:14 ` Juergen Gross
2015-06-22 14:22 ` Ian Jackson
2015-06-23 2:42 ` Chun Yan Liu
2015-06-23 2:43 ` Chun Yan Liu
2015-06-23 2:44 ` Chun Yan Liu
2015-06-16 10:41 ` [PATCH V4 3/7] libxl: add pvusb API Ian Jackson
2015-06-16 10:56 ` Jürgen Groß
2015-06-16 11:03 ` George Dunlap
2015-06-16 11:10 ` Ian Jackson
2015-06-16 11:25 ` Juergen Gross
2015-06-16 11:45 ` George Dunlap
2015-06-16 12:02 ` Ian Jackson
2015-06-16 13:19 ` George Dunlap
2015-06-16 13:32 ` Juergen Gross
2015-06-16 13:37 ` [PATCH V4 3/7] libxl: add pvusb API [and 1 more messages] Ian Jackson
2015-06-16 14:41 ` George Dunlap
2015-06-16 15:58 ` Sander Eikelenboom
2015-06-16 15:59 ` Ian Jackson
2015-06-16 16:34 ` George Dunlap
2015-06-17 3:59 ` Juergen Gross
2015-06-17 10:27 ` George Dunlap
2015-06-18 6:24 ` Chun Yan Liu [this message]
2015-06-16 11:45 ` [PATCH V4 3/7] libxl: add pvusb API Ian Jackson
2015-06-16 13:06 ` Juergen Gross
2015-06-16 13:09 ` George Dunlap
2015-06-16 13:23 ` Juergen Gross
2015-06-16 13:29 ` George Dunlap
2015-06-16 13:49 ` Juergen Gross
2015-06-16 14:06 ` George Dunlap
2015-06-16 14:20 ` Juergen Gross
2015-06-16 14:37 ` George Dunlap
2015-06-17 11:34 ` Ian Campbell
2015-06-17 11:40 ` Juergen Gross
2015-06-18 6:20 ` Chun Yan Liu
2015-06-18 7:02 ` Juergen Gross
2015-06-18 8:50 ` Ian Campbell
2015-06-18 13:02 ` Juergen Gross
2015-06-16 15:38 ` George Dunlap
2015-06-16 11:01 ` George Dunlap
2015-06-16 11:12 ` Ian Jackson
2015-06-16 11:21 ` George Dunlap
2015-06-16 16:32 ` Ian Jackson
2015-06-16 16:39 ` George Dunlap
2015-06-16 16:51 ` Ross Philipson
2015-06-17 4:03 ` Jürgen Groß
2015-06-17 13:48 ` Ross Philipson
2015-06-15 17:47 ` George Dunlap
2015-06-23 10:18 ` Chun Yan Liu
2015-06-23 11:29 ` George Dunlap
2015-06-24 2:26 ` Chun Yan Liu
2015-06-10 3:20 ` [PATCH V4 4/7] libxl: add libxl_device_usb_assignable_list API Chunyan Liu
2015-06-10 3:20 ` [PATCH V4 5/7] xl: add pvusb commands Chunyan Liu
2015-06-12 7:37 ` Juergen Gross
2015-06-12 8:03 ` Chun Yan Liu
2015-06-12 8:22 ` Juergen Gross
2015-06-10 3:20 ` [PATCH V4 6/7] xl: add usb-assignable-list command Chunyan Liu
2015-06-10 3:20 ` [PATCH V4 7/7] domcreate: support pvusb in configuration file Chunyan Liu
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