On Fri, Jun 24, 2022 at 10:31:06AM -0600, Shuah Khan wrote: > On 6/24/22 8:43 AM, Alan Stern wrote: > > > It doesn't sound like a there is a compelling reason other than > > > "it would be nice to keep the flag values in numerical order". > > > > > > I would not recommend this option. I am not seeing any value to adding > > > change URB_* to USBIP_FLAGS_* layer without some serious techinical > > > concerns. > > > > > > > > > > > Another way is to use 0x0400 for FREE_COHERENT. > > > > usbip will not take care of this bit as > > > > it would be masked. > > > > > > > > > > I would go with this option adding a clear comment with link to this > > > discussion. > > > > > > > Cc Shuah Khan here since she is the maintainer > > > > on usbip. > > > > > > > > > > Thank you adding me to the discussion. > > > > I can see this causing more problems in the future. There's no hint in > > include/linux/usb.h that any of the values it defines are part of a user > > API. If they are, they should be moved to include/uapi/linux/usb/. > > > > Please elaborate on more problems in the future. 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. > > In general, if a user program depends on kernel details that are not > > designed to be part of a user API, you should expect that the program > > will sometimes break from one kernel version to another. > > > > Yes, I know Linus insists that kernel changes should not cause > > regressions in userspace, but the line has to be drawn somewhere. > > Otherwise the kernel could never change at all. > > > > I have had to change the usbip sysfs interface api in the past to > address security bugs related to information leaks. I am not saying > no. I am asking if there is a good reason to do this. So far I haven't > heard one. I agree with Hongren that values defined in include/linux/ should not be part of a user API. There are two choices: Move the definitions into include/uapi/linux/, or 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.) Alan Stern
