From 91a30b70cedef704962ad428112da61a3f3b024d Mon Sep 17 00:00:00 2001
Message-Id: <91a30b70cedef704962ad428112da61a3f3b024d.1342518105.git.minovotn@redhat.com>
In-Reply-To: <27a73856ecc481c66c7afac8171f753887f32e31.1342518105.git.minovotn@redhat.com>
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From: Luiz Capitulino <lcapitulino@redhat.com>
Date: Tue, 5 Jun 2012 14:58:42 +0200
Subject: [PATCH 33/41] qemu-ga: become_daemon(): reopen standard fds to
/dev/null
RH-Author: Luiz Capitulino <lcapitulino@redhat.com>
Message-id: <1338908331-15633-28-git-send-email-lcapitulino@redhat.com>
Patchwork-id: 39925
O-Subject: [PATCH RHEL6.4 qemu-kvm 27/36] qemu-ga: become_daemon(): reopen standard fds to /dev/null
Bugzilla: 827612
RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
RH-Acked-by: Juan Quintela <quintela@redhat.com>
RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
This fixes a bug where qemu-ga doesn't suspend the guest because it
fails to detect suspend support even when the guest does support
suspend. This happens because of the way qemu-ga fds are managed in
daemon mode.
When starting qemu-ga with --daemon, become_daemon() will close all
standard fds. This will cause qemu-ga to end up with the following
fds (if started with 'qemu-ga --daemon'):
0 -> /dev/vport0p1
3 -> /run/qemu-ga.pid
Then a guest-suspend-* function is issued. They call bios_supports_mode(),
which will call pipe(), and qemu-ga's fd will be:
0 -> /dev/vport0p1
1 -> pipe:[16247]
2 -> pipe:[16247]
3 -> /run/qemu-ga.pid
bios_supports_mode() forks off a child and blocks waiting for the child
to write something to the pipe. The child, however, closes its reading
end of the pipe _and_ reopen all standard fds to /dev/null. This will
cause the child's fds to be:
0 -> /dev/null
1 -> /dev/null
2 -> /dev/null
3 -> /run/qemu-ga.pid
In other words, the child's writing end of the pipe is now /dev/null.
It writes there and exits. The parent process (blocked on read()) will
get an EOF and interpret this as "something unexpected happened in
the child, let's assume the guest doesn't support suspend". And suspend
will fail.
To solve this problem we have to reopen standard fds to /dev/null
in become_daemon(), instead of closing them.
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
(cherry picked from commit 226a48949cf74006a94b5931e50352b2af801ac7)
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
qemu-ga.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
Signed-off-by: Michal Novotny <minovotn@redhat.com>
---
qemu-ga.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/qemu-ga.c b/qemu-ga.c
index 8d53e04..6e7caed 100644
--- a/qemu-ga.c
+++ b/qemu-ga.c
@@ -445,9 +445,9 @@ static void become_daemon(const char *pidfile)
goto fail;
}
- close(STDIN_FILENO);
- close(STDOUT_FILENO);
- close(STDERR_FILENO);
+ reopen_fd_to_null(STDIN_FILENO);
+ reopen_fd_to_null(STDOUT_FILENO);
+ reopen_fd_to_null(STDERR_FILENO);
return;
fail:
--
1.7.10.4