Il 11/11/2013 17:56, Anthony Liguori ha scritto:
> On Mon, Nov 11, 2013 at 8:50 AM, Eric Blake <[email protected]> wrote:
>> Quick - identify the bug in this code (from ui/curses.c):
>>
>> static void curses_winch_handler(int signum)
>> {
>> struct winsize {
>> unsigned short ws_row;
>> unsigned short ws_col;
>> unsigned short ws_xpixel; /* unused */
>> unsigned short ws_ypixel; /* unused */
>> } ws;
>>
>> /* terminal size changed */
>> if (ioctl(1, TIOCGWINSZ, &ws) == -1)
>> return;
>>
>> resize_term(ws.ws_row, ws.ws_col);
>> curses_calc_pad();
>> invalidate = 1;
>>
>> /* some systems require this */
>> signal(SIGWINCH, curses_winch_handler);
>> }
>>
>> Here's a hint: ioctl() can clobber errno. But if a signal handler is
>> called in the middle of other code that is using errno, then the handler
>> MUST restore the value of errno before returning, if it is to guarantee
>> that the interrupted context won't be corrupted.
>
> Isn't this precisely why EINTR exists?
No.
do {
rc = read(...);
} while (rc == -1 && errno == EINTR);
/* signal handler runs here */
if (errno == EAGAIN) {
...
}
That said, aren't all signals in QEMU (except SIG_IPI) caught with
signalfd and the handlers run synchronously in the iothread?
Paolo
