From: "Chun Yan Liu" <cyliu@suse.com>
To: George Dunlap <George.Dunlap@eu.citrix.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Juergen Gross <JGross@suse.com>, Wei Liu <wei.liu2@citrix.com>,
Ian Campbell <ian.campbell@citrix.com>,
"xen-devel@lists.xen.org" <xen-devel@lists.xen.org>,
Jim Fehlig <JFEHLIG@suse.com>, Simon Cao <caobosimon@gmail.com>
Subject: Re: [PATCH V6 3/7] libxl: add pvusb API
Date: Thu, 17 Sep 2015 02:24:30 -0600 [thread overview]
Message-ID: <55FB055E0200006600050E86@relay2.provo.novell.com> (raw)
In-Reply-To: <CAFLBxZayaqTeJiB3RfG8qHxjCzQy8BBTe0Hxj+FT6ABSLf+Ntg@mail.gmail.com>
>>> On 9/14/2015 at 10:03 PM, in message
<CAFLBxZayaqTeJiB3RfG8qHxjCzQy8BBTe0Hxj+FT6ABSLf+Ntg@mail.gmail.com>, George
Dunlap <George.Dunlap@eu.citrix.com> wrote:
> On Mon, Sep 14, 2015 at 12:12 PM, Ian Jackson <Ian.Jackson@eu.citrix.com>
> wrote:
> > Juergen Gross writes ("Re: [Xen-devel] [PATCH V6 3/7] libxl: add pvusb
> API"):
> >> On 09/14/2015 12:36 PM, George Dunlap wrote:
> >> > Anyone want to look into the Linux source code to find out how big it
> >> > will allow busnum / devnum to grow?
> >>
> >> drivers/usb/core/hcd.c is using a bitmap to find the next bus number
> >> currently not in use. It's size is USB_MAXBUS which in turn has the
> >> value 64.
> >>
> >> choose_devnum() in drivers/usb/core/hub.c is doing a similar job for
> >> device numbers. Here the highest number supported is 127.
> >
> > We are defining an API, which shouldn't involve this kind of
> > implementation-grobbling.
> >
> > At an API level, it seems that this Linux busnum is not documented to
> > have any particular number or behaviour or range or anything. We
> > should use the biggest type we can use conveniently
> >
> > Do we need to worry that some bus might have 2^24 unplugs/plugs
> > (perhaps in some kind of software emulation) and that we need to use a
> > type which can hold a uint32_t or maybe even a uint64_t ?
>
> libusb is already a published API that supports uint8, or up to 255.
> Following their lead seems like a reasonable thing to do. If ever
> that number goes above 255, basically every Linux program that touches
> a USB device will need to be recompiled with a new version of libusb.
>
> Is there any reason for Linux to go above 255? Things I can think of:
>
> 1. Users have more than 255 devices plugged into the same bus.
>
> 2. A security / confusion issue due to devnum reuse when users plug
> and unplug devices hundreds of times.
>
> Both of these seem pretty unlikely.
>
> I would personally go with uint8, but int16 or int32 certainly won't hurt.
So can we agree to use uint8 for hostbus and hostaddr as libusb does?
>
> -George
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
>
>
next prev parent reply other threads:[~2015-09-17 8:24 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-10 10:35 [PATCH V6 0/7] xen pvusb toolstack work Chunyan Liu
2015-08-10 10:35 ` [PATCH V6 1/7] libxl: export some functions for pvusb use Chunyan Liu
2015-08-11 11:26 ` Wei Liu
2015-08-10 10:35 ` [PATCH V6 2/7] libxl_read_file_contents: add new entry to read sysfs file Chunyan Liu
2015-08-11 11:26 ` Wei Liu
2015-08-12 2:37 ` Chun Yan Liu
2015-08-13 9:11 ` Wei Liu
2015-08-10 10:35 ` [PATCH V6 3/7] libxl: add pvusb API Chunyan Liu
2015-08-11 11:27 ` Wei Liu
2015-08-12 2:24 ` Chun Yan Liu
2015-08-13 9:09 ` Wei Liu
2015-08-14 1:49 ` Chun Yan Liu
2015-08-18 2:31 ` Chun Yan Liu
2015-08-31 6:10 ` Chun Yan Liu
2015-09-08 14:17 ` Ian Campbell
2015-09-08 16:52 ` George Dunlap
2015-09-09 7:38 ` Chun Yan Liu
2015-09-17 8:19 ` Chun Yan Liu
2015-09-17 9:54 ` George Dunlap
2015-09-29 17:19 ` Wei Liu
2015-09-17 8:20 ` Chun Yan Liu
2015-09-11 5:42 ` Chun Yan Liu
2015-09-11 13:26 ` Ian Campbell
2015-09-11 13:55 ` Juergen Gross
2015-09-11 14:09 ` Ian Campbell
2015-09-11 14:18 ` Juergen Gross
2015-09-11 14:41 ` Ian Campbell
2015-09-11 15:42 ` Ian Jackson
2015-09-14 3:48 ` Juergen Gross
2015-09-14 10:36 ` George Dunlap
2015-09-14 10:53 ` Juergen Gross
2015-09-14 11:12 ` Ian Jackson
2015-09-14 11:23 ` Juergen Gross
2015-09-14 14:03 ` George Dunlap
2015-09-17 8:24 ` Chun Yan Liu [this message]
2015-09-15 8:14 ` Chun Yan Liu
2015-08-10 10:35 ` [PATCH V6 4/7] libxl: add libxl_device_usb_assignable_list API Chunyan Liu
2015-08-10 10:35 ` [PATCH V6 5/7] xl: add pvusb commands Chunyan Liu
2015-08-10 10:35 ` [PATCH V6 6/7] xl: add usb-assignable-list command Chunyan Liu
2015-08-10 10:35 ` [PATCH V6 7/7] domcreate: support pvusb in configuration file Chunyan Liu
2015-08-11 11:27 ` Wei Liu
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