[Qemu-devel] [PATCH 6/8] guest agent: ignore SIGPIPE signal

["Denis V. Lunev" <den@openvz.org>]

From: Simon Zolin <szolin@parallels.com>

If write operation fails on a pipe whose reading end is closed, qemu-ga
won't be terminated, but instead write() will fail with error EPIPE.

execve() inherits signals that are ignored, so reset SIGPIPE to its default
handler before calling execve() in a forked process.

Signed-off-by: Simon Zolin <szolin@parallels.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Michael Roth <mdroth@linux.vnet.ibm.com>
---
 qga/commands-posix.c | 16 ++++++++++++++++
 qga/main.c           |  6 ++++++
 2 files changed, 22 insertions(+)

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index d8e4ecf..bf9f79f 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -1030,6 +1030,20 @@ static int guest_exec_set_std(GuestFileHandle *gfh, int std_fd, int fd_null)
     return 0;
 }
 
+/** Reset ignored signals back to default. */
+static void guest_exec_reset_child_sig(void)
+{
+    struct sigaction sigact;
+
+    memset(&sigact, 0, sizeof(struct sigaction));
+    sigact.sa_handler = SIG_DFL;
+
+    if (sigaction(SIGPIPE, &sigact, NULL) != 0) {
+        slog("sigaction() failed to reset child process's SIGPIPE: %s",
+             strerror(errno));
+    }
+}
+
 int64_t qmp_guest_exec(const char *path,
                        bool has_params, strList *params,
                        bool has_env, strList *env,
@@ -1102,6 +1116,8 @@ int64_t qmp_guest_exec(const char *path,
             /* exit(1); */
         }
 
+        guest_exec_reset_child_sig();
+
         execvpe(path, (char * const *)argv, (char * const *)envp);
         slog("guest-exec child failed: %s", strerror(errno));
         exit(1);
diff --git a/qga/main.c b/qga/main.c
index 9939a2b..bc6414c 100644
--- a/qga/main.c
+++ b/qga/main.c
@@ -160,6 +160,12 @@ static gboolean register_signal_handlers(void)
         g_error("error configuring signal handler: %s", strerror(errno));
     }
 
+    sigact.sa_handler = SIG_IGN;
+    if (sigaction(SIGPIPE, &sigact, NULL) != 0) {
+        g_error("error configuring SIGPIPE signal handler: %s",
+                strerror(errno));
+    }
+
     return true;
 }
 
-- 
1.9.1