On Fri, 2016-09-16 at 18:24 +0200, Julio Guerra wrote: > > On Sat, 2016-08-20 at 14:14 +0200, Julio Guerra wrote: > >>>> Another example: > >>>>> 00 00 00 00 00 00 00 01 > >>>> ... > >>>>> 01 00 00 00 00 00 00 00 > >>>> ... > >>>>> 00 01 00 00 00 00 00 00 > >>>> ... > >>>>> 00 00 01 00 00 00 00 00 > >>>> after a random number of times, while usbmon shows the usb payload > >>>> "00 00 00 00 00 00 00 01". > >>> > >>> Hi, how many bytes does read() return? > >>> > >> > >> Exactly 8 bytes, always. I set the tty in raw non-canonical mode with > >> vmin = 8 and vtime = 0. I also tried with vmin = 1 and did the copy of > >> exactly 8 bytes by looping in userspace, without any improvement. > >> > >> I wrote a small workaround for now that detects this problem (because I > >> exactly know what the buffer is supposed to look like) to close() and > >> re-open() the device. The next read buffer is then correct. > >> > > > > Please activate dynamic debugging for the tty and cdc_acm driver. > > We need to know where the corruption happens. > > > > I didn't find anything helpful in /sys/kernel/debug/dynamic_debug > regarging the tty module (I enabled tty_io debugs and it doesn't appear > in the logs), but I enabled cdc_acm debugs. Nothing is observable in the > logs when the bug appears. I logged everything as a comment of the gist: > https://gist.github.com/Julio-Guerra/b6529994f814771c825649bdb8d927c2#gistcomment-1875985 > > Note that re-running the script restarts the underlying kernel buffer > correctly, it does not restart from its previous bugged state. > > Let me know if you want other debug traces enabled. > Can you modify the tty layer to print out the buffer? It is unclear from the logs where the shift happens. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
