From: Ian Jackson Date: Thu, 2 Apr 2015 14:32:22 +0000 (+0100) Subject: Revert "tools/libxl: Adjust datacopiers POLLHUP handling when the fd is also readable" X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~3462 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=1a362e2a36dd06d748531917d07dbab42fe0eae3;p=xen.git Revert "tools/libxl: Adjust datacopiers POLLHUP handling when the fd is also readable" The bootloader code is relying on detecting POLLHUP, and 7e9ec50b breaks that. 7e9ec50b, when handling a pty master, violates the specification of the datacopier interface (as defined). When the bootloader exits, several things change, all at once: (a) The master pty fd (held by libxl) starts to signal POLLHUP and maybe also POLLIN. (b) The child exits (so that the SIGCHLD self-pipe signals POLLIN, which will be handled by the libxl child process code. (c) reads on the master pty fd start to return EOF From the point of view of the datacopier these might happen in any order. I think there is a latent bug with (c), which I will discuss later in this email. In a recent bug report from a FreeBSD installation, the datacopier gets told about (a) before (b). But 7e9ec50b filters the POLLHUP out, so that the dc signals eof rather than hup. As a result in bootloader_copyfail we take the error path. This reverts commit 7e9ec50b0535bf2630da9d279a060775817d136d. Signed-off-by: Ian Jackson Acked-by: Andrew Cooper CC: Andrew Cooper CC: Roger Pau Monné CC: Ian Campbell CC: Ross Lagerwall CC: Wei Liu --- diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c index da102a04e9..3942634314 100644 --- a/tools/libxl/libxl_aoutils.c +++ b/tools/libxl/libxl_aoutils.c @@ -205,9 +205,6 @@ static void datacopier_readable(libxl__egc *egc, libxl__ev_fd *ev, libxl__datacopier_state *dc = CONTAINER_OF(ev, *dc, toread); STATE_AO_GC(dc->ao); - if ((revents & (POLLHUP|POLLIN)) == (POLLHUP|POLLIN)) - revents &= ~POLLHUP; - if (datacopier_pollhup_handled(egc, dc, revents, 0)) return;