In article <25389.33419.131713.821...@gargle.gargle.howl>, Anthony Mallet <anthony.mal...@laas.fr> wrote: >-=-=-=-=-=- > >Hi, > >I have a piece of software that opens a master pty non-blocking: >fd = open("/dev/ptmx", O_RDWR | O_NOCTTY | O_NONBLOCK); > >The intent is to make further read(2) on the master non blocking. But >the O_NONBLOCK flag seems to be ignored. Attached is a minimal sample >C program showing the issue. > >Several remarks: >* open(2) manual does not mention a master pty as special regarding the > O_NONBLOCK flag, and even says "this flag also has the effect of making > all subsequent I/O on the open file non-blocking", >* explicitly setting the file descriptor as non-blocking with fcntl(2) > works fine, >* a slave pty has no such issue (O_NONBLOCK in open(2) is honoured), >* FWIW, linux has no surprise here, the flag behaves as one would expect, >* POSIX does not mention the flag as supported in posix_openpt(3) (it > does not says it's not supported either :). > >So, I'm not sure if something should be changed here, and if someone >is willing to check that? I tried to track down where in the kernel >this happens, maybe in pty_alloc_master in kern/tty_ptm.c? I really >don't master those kernel aspects so I'm not confident in providing a >patch. > >I guess the principle of least surprise would say that the flag should >be supported (e.g. for maximum portability). OTOH, if the current >behaviour is deemed correct or sufficient, maybe at least some manual >(posix_openpt, open, ...) should mention this is not supported? > >Best, >Anthony
Fixed in HEAD. christos