On Monday 01 October 2007 20:04, Davide Libenzi wrote: > > They don't even need to read in parallel, just having shared fd is enough. > > Think about pipes, sockets and terminals. A real-world scenario: > > > > * a process started from shell (interactive or shell script) > > * it sets O_NONBLOCK and does a read from fd 0... > > * it gets killed (kill -9, whatever) > > * shell suddenly has it's fd 0 in O_NONBLOCK mode > > * shell and all subsequent commands started from it unexpectedly have > > O_NONBLOCKed stdin. > > I told you how in the previous email. You cannot use the: > > 1) set O_NONBLOCK > 2) read/write > 3) unset O_NONBLOCK > > in a racy-free fashion, w/out wrapping it with a lock (thing that we > don't want to do).
I'm confused. I am saying exactly this same thing: that I cannot do it atomically using standard unix operations, but I still need to do a nonblocking read. Why are you explaining to me that it cannot be done? I *know*. I'm asking what API should be added/extended to make it possible. I have following proposals: * make recv(..., MSG_DONTWAIT) work on any fd Sounds neat, but not trivial to implement in current kernel. * new fcntl command F_DUPFL: fcntl(fd, F_DUPFL, n): Analogous to F_DUPFD, but gives you *unshared* copy of the fd. Further seeks, fcntl(fd, F_SETFL, O_NONBLOCK), etc won't affect any other process. How hard would it be implement F_DUPFL in current kernel? -- vda - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
