On Tue. 2 Aug. 2022 at 02:48, Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx> wrote: > On 6/30/22 8:10 PM, Shuah Khan wrote: > > On 6/27/22 7:35 PM, Alan Stern wrote: > >> On Mon, Jun 27, 2022 at 04:54:17PM -0600, Shuah Khan wrote: > >>> On 6/24/22 12:07 PM, Alan Stern wrote: > >>>> In the future people will want to make other changes to > >>>> include/linux/usb.h and they will not be aware that those changes will > >>>> adversely affect usbip, because there is no documentation saying that > >>>> the values defined in usb.h are part of a user API. That will be a > >>>> problem, because those changes may be serious and important ones, not > >>>> just decorative or stylistic as in this case. > >>>> > >>> > >>> How often do these values change based on our past experience with these > >>> fields? > >> > >> I don't know. You could check the git history to find out for certain. > >> My guess would be every eight or ten years. > >> > >>>> I agree with Hongren that values defined in include/linux/ should not be > >>>> part of a user API. There are two choices: > >>>> > >>> > >>> I agree with this in general. I don't think this is an explicit decision > >>> to make them part of API. It is a consequence of simply copying the > >>> transfer_flags. I am with you both on not being able to recognize the > >>> impact until as this is rather obscure usage hidden away in the packets. > >>> These defines aren't directly referenced. > >>> > >>>> Move the definitions into include/uapi/linux/, or > >>>> > >>> > >>> Wouldn't this be easier way to handle the change? With this option > >>> the uapi will be well documented. > >>> > >>>> Add code to translate the values between the numbers used in > >>>> userspace and the numbers used in the kernel. (This is what > >>>> was done for urb->transfer_flags in devio.c:proc_do_submiturb() > >>>> near line 1862.) > >>>> > >>> > >>> I looked at the code and looks simple enough. I am okay going this route > >>> if we see issues with the option 1. > >> > >> It's up to you; either approach is okay with me. However, I do think > >> that the second option is a little better; I don't see any good reason > >> why the kernel should be forced to use the same numeric values for these > >> flags forever. Especially since the only user program that needs to > >> know them is usbip, which is fairly closely tied to the kernel; if there > >> were more programs using those values then they would constitute a good > >> reason for choosing the first option. > >> > > > > Thank you Alan and Hongren for your help with this problem. Since there > > are no changes to the flags for the time being, I am comfortable going > > with the second option. > > > > I will send a patch soon. > > > > Patch is almost ready to be sent out. Changes aren't bad at all. Hoping to > get this done sooner - summer vacations didn't cooperate. > > Just an update that I haven't forgotten and it will taken care of. > thanks, Thanks for keeping this under your radar. I also have on my TODO list to send a new version of my patch to add the `URB_FREE_COHERENT' flag but this time adding an `allocated_length' field to struct urb. I will wait for your patch to go first. By the way, I will be out for summer holiday for the next couple of weeks so I wasn't planning to submit anything soon regardless. Yours sincerely, Vincent Mailhol
