On Tue, 1 Mar 2016, Felipe Balbi wrote: > Hi, > > Robert Baldyga <r.bald...@samsung.com> writes: > >> Olivier Schonken <olivier.schon...@gmail.com> writes: > >>> Hope I'm not raising an issue which actually is my own stupidity. > >>> > >>> I recently upstreamed my embedded Linux kernel to version 4.4, after which > >>> I started experiencing issues with my serial gadget - acm and obex. I > >>> used > >>> to be able to run a getty console on it through a systemd service, which > >>> would restart everytime it was unplugged, and plugged in again. With > >>> kernel 4.4, this stopped working as usual(On startup console would word, > >>> but if plugged out and in again, console is frozen), and I traced it back > >>> to the series of patches "usb: gadget: introduce 'enabled' flag in struct > >>> usb_ep". If I revert these patches, everything works as normal again. As > >>> you are the owner of these patches, I thought that you might help me > >>> understand if I'm doing something wrong w.r.t. re-initializing the console > >>> getty, or if something really got broken. > >> > >> This is short of email where the mailing list should be in Cc :-) > >> > >> The author of that series was Robert (now in Cc). Robert, does this ring > >> any bells to you ? > >> > > > > I have tested it with getty (without systemd) and it looks like getty > > hangs up after replugging no matter if patch is applied or not, so > > without systemd it won't work anyway. > > > > Hence how systemd handles this is the key here, however I have no idea > > how systemd knows that USB device is unplugged. On device side > > /dev/ttyGS0 exists regardless to ACM function state, so process which > > opened this device file has no way to figure out whether connection to > > host is active or not. Can you explain how systemd knows that device is > > unplugged? This knowledge can be helpful. > > there should be a SIGHUP when cable's removed, no ?
More to the point, udev is now part of systemd, and udev certainly knows when a device has been added or removed. It gets messages directly from the kernel whenever one of those events occurs. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
