Initially I proposed a similar patch here:
http://thread.gmane.org/gmane.comp.emulators.libvirt/20607
That thread languished, and Eric proposed a nearly identical patch:
http://thread.gmane.org/gmane.comp.emulators.libvirt/21630
Here's a patch that should address the initial objection.
Now, my only question is about which errno values to ignore.
Obviously, EMFILE, EFAULT, etc. must not be ignored.
I doubt EINTR and EBADF should be ignored, but haven't
tried to prove the case.
>From 6dcd15b0aa594f3d89e810e0a92aa75dab22903e Mon Sep 17 00:00:00 2001
From: Jim Meyering <meyering@xxxxxxxxxx>
Date: Thu, 20 May 2010 14:30:36 +0200
Subject: [PATCH] lxc_controller.c: don't ignore failed "accept"
* src/lxc/lxc_controller.c (ignorable_epoll_accept_errno): New function.
(lxcControllerMain): Handle a failed accept carefully:
most errno values indicate legitimate failure and must be fatal.
However, ignore a special case: that in which an incoming client quits
between the poll() indicating its presence, and our accept() which
is trying to process it.
---
src/lxc/lxc_controller.c | 23 +++++++++++++++++++++++
1 files changed, 23 insertions(+), 0 deletions(-)
diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
index 6b64372..75a45e9 100644
--- a/src/lxc/lxc_controller.c
+++ b/src/lxc/lxc_controller.c
@@ -269,6 +269,17 @@ typedef struct _lxcTtyForwardFd_t {
int active;
} lxcTtyForwardFd_t;
+/* Return true if it is ok to ignore an accept-after-epoll syscall
+ that fails with the specified errno value. Else false. */
+static bool
+ignorable_epoll_accept_errno(int erratum)
+{
+ return (errnum == EINVAL
+ || errnum == ECONNABORTED
+ || errnum == EAGAIN
+ || errnum == EWOULDBLOCK);
+}
+
/**
* lxcControllerMain
* @monitor: server socket fd to accept client requests
@@ -350,6 +361,18 @@ static int lxcControllerMain(int monitor,
if (numEvents > 0) {
if (epollEvent.data.fd == monitor) {
int fd = accept(monitor, NULL, 0);
+ if (fd < 0) {
+ /* First reflex may be simply to declare accept failure
+ to be a fatal error. However, accept may fail when
+ a client quits between the above epoll_wait and here.
+ That case is not fatal, but rather to be expected,
+ if not common, so ignore it. */
+ if (ignorable_epoll_accept_errno(errno))
+ continue;
+ virReportSystemError(errno, "%s",
+ _("accept(monitor,...) failed"));
+ goto cleanup;
+ }
if (client != -1) { /* Already connected, so kick new one out */
close(fd);
continue;
--
1.7.1.262.g5ef3d
--
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