Re: [PATCH] tools: usb: usbip: adding support for older kernel versions

From: shuah
Date: Mon Mar 25 2019 - 11:51:25 EST

On 3/18/19 12:23 PM, Brian Norris wrote:
On Sat, Mar 16, 2019 at 4:40 PM shuah <shuah@xxxxxxxxxx> wrote:
usbip tool is tied to the kernel version. This is reason why it is
co-located with the usbip driver in the kernel sources. This is not
a typical tool scenario to be able to use new tool on old kernels.

I would like to understand the reasons for wanting to run new tool on
old kernels.

On Chromium OS, we ship more or less the same user space for a variety
of systems, but not all of those run the same kernel. That's not
exactly a novel concept -- many good tools are written such that they
degrade gracefully when running with reduced feature sets (e.g., older
kernels). While we are working on reducing the divergence and number
of kernels we ship, it's currently a fact of life that we have to
support multiple target kernel versions.

Thanks for the context for this change.

Is there a fundamental problem with VHCI such that it doesn't have a
stable ABI that tools can be written against?

In general the ABI is stable.

+#define V3_18_STATUS_HEADER "prt sta spd bus dev socket local_busid"

What's your 3.18 kernel version? I think you are missing security
fixes that prevent socket address leak in the status file.

+#define V4_4_STATUS_HEADER "prt sta spd dev sockfd local_busid"
+#define V4_14_STATUS_HEADER "hub port sta spd dev sockfd local_busid"

The difference here is the high speed support. Let's find a better
way to fix this than hard-coding kernel revisions in the tool.

If stability is possible but you just don't care, then I guess we can
fork our own version...

Or even worse, we could build N copies of usbip for N kernels. But we
don't do that for any other user space component.

It might be easier to build N versions than maintaining the fork :)

In any case, let's find ways to fix the problem with a constructive

-- Shuah