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authorLuiz Capitulino <lcapitulino@redhat.com>2012-05-11 16:19:46 -0300
committerMichael Roth <mdroth@linux.vnet.ibm.com>2012-05-15 09:15:16 -0500
commitdc8764f06155a7b3e635e02281b747a9e292127e (patch)
tree7191954c7f6d4157e6f98c869344c1d065084017 /qga
parent226a48949cf74006a94b5931e50352b2af801ac7 (diff)
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qemu-ga: guest-suspend: make the API synchronous
Currently, qemu-ga has a SIGCHLD handler that automatically reaps terminated children processes. The idea is to avoid having qemu-ga commands blocked waiting for children to terminate. That approach has two problems: 1. qemu-ga is unable to detect errors in the child, meaning that qemu-ga returns success even if the child fails to perform its task 2. if a command does depend on the child exit status, the command has to play tricks to bypass the automatic reaper Case 2 impacts the guest-suspend-* API, because it has to execute an external program to check for suspend support. Today, to bypass the automatic reaper, suspend code has to double fork and pass exit status information through a pipe. Besides being complex, this is prone to race condition bugs. Indeed, the current code does have such bugs. Making the guest-suspend-* API synchronous (ie. by dropping the SIGCHLD handler and calling waitpid() from commands) is a much simpler approach, which fixes current race conditions bugs and enables commands to detect errors in the child. This commit does just that. There's a side effect though, guest-shutdown will generate zombies if shutting down fails. This will be fixed by the next commit. 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>
Diffstat (limited to 'qga')
-rw-r--r--qga/commands-posix.c128
1 files changed, 54 insertions, 74 deletions
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index adb9b3d..76c8235 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -512,117 +512,88 @@ static void guest_fsfreeze_cleanup(void)
#define SUSPEND_SUPPORTED 0
#define SUSPEND_NOT_SUPPORTED 1
-/**
- * This function forks twice and the information about the mode support
- * status is passed to the qemu-ga process via a pipe.
- *
- * This approach allows us to keep the way we reap terminated children
- * in qemu-ga quite simple.
- */
static void bios_supports_mode(const char *pmutils_bin, const char *pmutils_arg,
const char *sysfile_str, Error **err)
{
- pid_t pid;
- ssize_t ret;
char *pmutils_path;
- int status, pipefds[2];
-
- if (pipe(pipefds) < 0) {
- error_set(err, QERR_UNDEFINED_ERROR);
- return;
- }
+ pid_t pid, rpid;
+ int status;
pmutils_path = g_find_program_in_path(pmutils_bin);
pid = fork();
if (!pid) {
- struct sigaction act;
-
- memset(&act, 0, sizeof(act));
- act.sa_handler = SIG_DFL;
- sigaction(SIGCHLD, &act, NULL);
+ char buf[32]; /* hopefully big enough */
+ ssize_t ret;
+ int fd;
setsid();
- close(pipefds[0]);
reopen_fd_to_null(0);
reopen_fd_to_null(1);
reopen_fd_to_null(2);
- pid = fork();
- if (!pid) {
- int fd;
- char buf[32]; /* hopefully big enough */
-
- if (pmutils_path) {
- execle(pmutils_path, pmutils_bin, pmutils_arg, NULL, environ);
- }
-
- /*
- * If we get here either pm-utils is not installed or execle() has
- * failed. Let's try the manual method if the caller wants it.
- */
-
- if (!sysfile_str) {
- _exit(SUSPEND_NOT_SUPPORTED);
- }
-
- fd = open(LINUX_SYS_STATE_FILE, O_RDONLY);
- if (fd < 0) {
- _exit(SUSPEND_NOT_SUPPORTED);
- }
+ if (pmutils_path) {
+ execle(pmutils_path, pmutils_bin, pmutils_arg, NULL, environ);
+ }
- ret = read(fd, buf, sizeof(buf)-1);
- if (ret <= 0) {
- _exit(SUSPEND_NOT_SUPPORTED);
- }
- buf[ret] = '\0';
+ /*
+ * If we get here either pm-utils is not installed or execle() has
+ * failed. Let's try the manual method if the caller wants it.
+ */
- if (strstr(buf, sysfile_str)) {
- _exit(SUSPEND_SUPPORTED);
- }
+ if (!sysfile_str) {
+ _exit(SUSPEND_NOT_SUPPORTED);
+ }
+ fd = open(LINUX_SYS_STATE_FILE, O_RDONLY);
+ if (fd < 0) {
_exit(SUSPEND_NOT_SUPPORTED);
}
- if (pid > 0) {
- wait(&status);
- } else {
- status = SUSPEND_NOT_SUPPORTED;
+ ret = read(fd, buf, sizeof(buf)-1);
+ if (ret <= 0) {
+ _exit(SUSPEND_NOT_SUPPORTED);
}
+ buf[ret] = '\0';
- ret = write(pipefds[1], &status, sizeof(status));
- if (ret != sizeof(status)) {
- _exit(EXIT_FAILURE);
+ if (strstr(buf, sysfile_str)) {
+ _exit(SUSPEND_SUPPORTED);
}
- _exit(EXIT_SUCCESS);
+ _exit(SUSPEND_NOT_SUPPORTED);
}
- close(pipefds[1]);
g_free(pmutils_path);
if (pid < 0) {
- error_set(err, QERR_UNDEFINED_ERROR);
- goto out;
- }
-
- ret = read(pipefds[0], &status, sizeof(status));
- if (ret == sizeof(status) && WIFEXITED(status) &&
- WEXITSTATUS(status) == SUSPEND_SUPPORTED) {
- goto out;
+ goto undef_err;
+ }
+
+ do {
+ rpid = waitpid(pid, &status, 0);
+ } while (rpid == -1 && errno == EINTR);
+ if (rpid == pid && WIFEXITED(status)) {
+ switch (WEXITSTATUS(status)) {
+ case SUSPEND_SUPPORTED:
+ return;
+ case SUSPEND_NOT_SUPPORTED:
+ error_set(err, QERR_UNSUPPORTED);
+ return;
+ default:
+ goto undef_err;
+ }
}
- error_set(err, QERR_UNSUPPORTED);
-
-out:
- close(pipefds[0]);
+undef_err:
+ error_set(err, QERR_UNDEFINED_ERROR);
}
static void guest_suspend(const char *pmutils_bin, const char *sysfile_str,
Error **err)
{
- pid_t pid;
char *pmutils_path;
+ pid_t rpid, pid;
+ int status;
pmutils_path = g_find_program_in_path(pmutils_bin);
@@ -664,9 +635,18 @@ static void guest_suspend(const char *pmutils_bin, const char *sysfile_str,
g_free(pmutils_path);
if (pid < 0) {
- error_set(err, QERR_UNDEFINED_ERROR);
+ goto exit_err;
+ }
+
+ do {
+ rpid = waitpid(pid, &status, 0);
+ } while (rpid == -1 && errno == EINTR);
+ if (rpid == pid && WIFEXITED(status) && !WEXITSTATUS(status)) {
return;
}
+
+exit_err:
+ error_set(err, QERR_UNDEFINED_ERROR);
}
void qmp_guest_suspend_disk(Error **err)