On Mon, Mar 25, 2019 at 3:07 PM shuah <shuah@xxxxxxxxxx> wrote: > On 3/25/19 11:56 AM, Brian Norris wrote: > > On Mon, Mar 25, 2019 at 8:51 AM shuah <shuah@xxxxxxxxxx> wrote: > >> In general the ABI is stable. > > > > No, it really isn't. This commit was a breaking change: ... > > But this one is definitely a break: > > > > commit 1c9de5bf428612458427943b724bea51abde520a > > Author: Yuyang Du <yuyang.du@xxxxxxxxx> > > Date: Thu Jun 8 13:04:10 2017 +0800 > > > > usbip: vhci-hcd: Add USB3 SuperSpeed support > > > > You can't just arbitrarily add columns to the beginning of a file like > > that and claim that you're not breaking ABI. And I shouldn't need to > > remind you that Thou Shalt Not Break User Space. > > USB 3.0 driver and tool support went in, I would say it was oversight to > not make sure the tool continues to work on older kernels. While that's true, you're still not grokking my main point when asking about ABI stability: *old* tools should still work on *new* kernels The above commit broke that. > So what's your ability to upgrade to 3.18 latest to get the security > fix. You would want to pick this up anyway. We'll take cherry-picks as needed. You don't need to worry about exactly how we maintain our branches, as that's not really the main concern of upstream (at least, not in terms of kernel development). But for the purposes of this conversation, assume that we have that bugfix. > Now the second issue is "supporting the latest tool on older kernels". > Guess I didn't think about the possibility of tools from 5.1 being run > on 3.18 :) > > I am willing to guarantee that going forward the latest usbip tool > will not break on the supported stable releases. > > I am going to take a look at fixing the tool to run on older kernels. That would be appreciated, but frankly, even that is not really required: if you want to maintain the tool such that it always assumes the latest kernel features that's your prerogative -- we don't have to upgrade every release. At some point, new software tends to require some minimal dependencies beneath it. So again, it would be nice to degrade gracefully on older kernels, but it's not an absolute requirement. The biggest issue, as noted above, is that I currently cannot run older usbip (user space) on newer kernels. That's a flagrant violation of kernel ABI guarantees. If you did consistently maintain ABI as noted above (old user space; new kernel), then your users can choose to upgrade user space only when needed. (And so, for instance, I could solve my problem by simply downgrading to usbip tools from 3.18.) Today, that's not possible. Brian
