On Mon, 2011-06-06 at 13:59 -0400, Devin Heitmueller wrote: > On Mon, Jun 6, 2011 at 1:56 PM, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > > Hi, > > > > While working on my cleanup / v4l2 compliance series for > > the pwc driver I've noticed that the pwc and gspca drivers > > are doing different things wrt what error they return to > > an app is using the device while it gets unplugged. > > gspca returns -ENODEV, where as pwc returns -EPIPE. > > > > Both make some sense. I've not looked at what other > > usb (or other hotplug capable bus) v4l2 drivers do, but > > it makes sense to me to standardize on an error here, > > preferably a reasonable unique one so that apps can > > detect unplug versus other errors. Note that the usb > > subsystem returns -ENODEV when you try to (re)submit > > an urb from its completion handler, when that > > completion handler gets called because the urb was > > unlinked because of device unplug. > > > > Given that we often return usb error codes unmodified > > and the usb subsys uses -ENODEV for trying to do things > > with unplugged devices, I guess it makes sense for > > us to also use -ENODEV. > > I'm pretty sure ENODEV is what gets returned today if you attempt to > open a /dev/videoX node for a device that has been disconnected but > the device node hasn't yet been removed. So I would agree that ENODEV > is a good choice for the scenario you described. Neither ENODEV nor EPIPE are correct. POSIX requires ENXIO in this situation. http://pubs.opengroup.org/onlinepubs/9699919799/ http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_03 Section 2.3 describes the error numbers. Here are some highlights: [EIO] Input/output error. Some physical input or output error has occurred. This error may be reported on a subsequent operation on the same file descriptor. Any other error-causing operation on the same file descriptor may cause the [EIO] error indication to be lost. [ENODEV] No such device. An attempt was made to apply an inappropriate function to a device; for example, trying to read a write-only device such as a printer. [ENXIO] No such device or address. Input or output on a special file refers to a device that does not exist, or makes a request beyond the capabilities of the device. It may also occur when, for example, a tape drive is not on-line. [EPIPE] Broken pipe. A write was attempted on a socket, pipe, or FIFO for which there is no process to read the data. Also, Appendix A of "POSIX and Linux Application Compatibility Design Rules" https://www.opengroup.org/platform/single_unix_specification/uploads%/40/13450/POSIX_and_Linux_Application_Compatibility_Final_-_v1.0.pdf has this note: "Formerly, Linux permited several file system functions to return either ENODEV or ENXIO for a non-existent device, while POSIX requires an ENXIO return in this case. Linux now returns the correct error under this condition. This applied to fopen(), freopen(), open(), and creat()." Regards, Andy -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
