From: Ian Jackson <Ian.Jackson@eu.citrix.com>
To: George Dunlap <george.dunlap@eu.citrix.com>
Cc: "Jürgen Groß" <jgross@suse.com>, "Wei Liu" <wei.liu2@citrix.com>,
"Ian Campbell" <ian.campbell@citrix.com>,
"Chunyan Liu" <cyliu@suse.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
"Jim Fehlig" <jfehlig@suse.com>,
"Simon Cao" <caobosimon@gmail.com>
Subject: Re: [PATCH V4 3/7] libxl: add pvusb API [and 1 more messages]
Date: Tue, 16 Jun 2015 16:59:36 +0100 [thread overview]
Message-ID: <21888.18408.443895.592922@mariner.uk.xensource.com> (raw)
In-Reply-To: <558035B0.3070308@eu.citrix.com>
George Dunlap writes ("Re: [Xen-devel] [PATCH V4 3/7] libxl: add pvusb API [and 1 more messages]"):
> On 06/16/2015 02:37 PM, Ian Jackson wrote:
> > George Dunlap writes ("Re: [Xen-devel] [PATCH V4 3/7] libxl: add pvusb API"> >> /sys/devices/pci0000:00/0000:00:1d.7/usb2/2-3/2-3.3/. This contains
> >> the pci bus address, but it also contains the bus number, which we've
> >> just said may be unstable across reboots.
> >
> > You mean the 2 in `usb2' ? I think that bus number is the bus number
> > within the controller, not globally.
>
> On the contrary:
> [...]
Oh dear.
> In other words, the global bus enumeration leaks its way into the device
> path; which means at very least the sysfs device path is potentially
> unstable across reboots even if you include the pci controller it's on.
How unhelpful.
> > 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:
zealot:~> ls -al /dev/disk/by-path/pci-0000:00:1d.7-usb-0:1:1.0-scsi-0:0:0:0-part1
lrwxrwxrwx 1 root root 10 Jun 16 16:45 /dev/disk/by-path/pci-0000:00:1d.7-usb-0:1:1.0-scsi-0:0:0:0-part1 -> ../../sdc1
zealot:~> ls -al /sys/class/block/sdc
lrwxrwxrwx 1 root root 0 Jun 16 16:45 /sys/class/block/sdc -> ../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1:1.0/host19/target19:0:0/19:0:0:0/block/sdc/
zealot:~>
Observe that the sysfs path contains not only `usb1' (which isn't
stable) but also `host19' which is also not stable. If I unplug and
replug:
zealot:~> ls -al /dev/disk/by-path/pci-0000:00:1d.7-usb-0:1:1.0-scsi-0:0:0:0-part1
lrwxrwxrwx 1 root root 10 Jun 16 16:49 /dev/disk/by-path/pci-0000:00:1d.7-usb-0:1:1.0-scsi-0:0:0:0-part1 -> ../../sdc1
zealot:~> ls -al /sys/class/block/sdc
lrwxrwxrwx 1 root root 0 Jun 16 16:50 /sys/class/block/sdc -> ../../devices/pci0000:00/0000:00:1d.7/usb1/1-1/1-1:1.0/host20/target20:0:0/20:0:0:0/block/sdc/
zealot:~>
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.
I can't seem to find anything relevant in my
/sys/devices/pci0000:00/0000:00:1d.7
> > I think the hardware path to the controller, at least, should be
> > treated as an opaque OS-specific string. It might have a different
> > format on BSD.
>
> If we can make an actual path that's stable across reboots, that would
> certainly be a good thing. But if it's not stable across reboots, it
> has no advantage over the bus-port[.port.port] interface.
Yes.
Ian.
next prev parent reply other threads:[~2015-06-16 15:59 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=21888.18408.443895.592922@mariner.uk.xensource.com \
--to=ian.jackson@eu.citrix.com \
--cc=caobosimon@gmail.com \
--cc=cyliu@suse.com \
--cc=george.dunlap@eu.citrix.com \
--cc=ian.campbell@citrix.com \
--cc=jfehlig@suse.com \
--cc=jgross@suse.com \
--cc=wei.liu2@citrix.com \
--cc=xen-devel@lists.xen.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.