Messages in this thread | | | From | "Miquel van Smoorenburg" <> | Subject | Re: F_DUPFD_CLOEXEC implementation | Date | 01 Oct 2007 00:59:14 GMT |
| |
In article <200709300131.49320.vda.linux@googlemail.com>, Denys Vlasenko <vda.linux@googlemail.com> wrote: >Hi Ulrich, > >On Friday 28 September 2007 18:34, Ulrich Drepper wrote: >> One more small change to extend the availability of creation of >> file descriptors with FD_CLOEXEC set. Adding a new command to >> fcntl() requires no new system call and the overall impact on >> code size if minimal. > >Tangential question: do you have any idea how userspace can >safely do nonblocking read or write on a potentially-shared fd? > >IIUC, currently it cannot be done without races: > >old_flags = fcntl(fd, F_GETFL); >...other process may change flags!... >fcntl(fd, F_SETFL, old_flags | O_NONBLOCK); >read(fd, ...) >...other process may see flags changed under its feet!... >fcntl(fd, F_SETFL, old_flags); > >Can this be fixed?
This is for sockets, right ? Just use revc() instead of read().
n = recv(filedesc, buffer, buflen, MSG_DONTWAIT);
.. is equivalent to setting O_NONBLOCK. See "man recv".
Mike. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |