[Qemu-devel] [PATCH 1/3] qemu-ga: add guest-suspend-disk

[Luiz Capitulino <lcapitulino@redhat.com>]

As the command name implies, this command suspends the guest to disk.

The suspend operation is implemented by two functions: bios_supports_mode()
and guest_suspend(). Both functions are generic enough to be used by
other suspend modes (introduced by next commits).

Both functions will try to use the scripts provided by the pm-utils
package if it's available. If it's not available, a manual method,
which consists of directly writing to '/sys/power/state', will be used.

To reap terminated children, a new signal handler is installed in the
parent to catch SIGCHLD signals and a non-blocking call to waitpid()
is done to collect their exit statuses. The statuses, however, are
discarded.

The approach used to query the guest for suspend support deserves some
explanation. It's implemented by bios_supports_mode() and shown below:

  qemu-ga
     |
 create pipe
     |
   fork()
     -----------------
     |               |
     |               |
     |             fork()
     |               --------------------------
     |               |                        |
     |               |                        |
     |               |               exec('pm-is-supported')
     |               |
     |              wait()
     |       write exit status to pipe
     |              exit
     |
  read pipe

This might look complex, but the resulting code is quite simple.
The purpose of that approach is to allow qemu-ga to reap its children
(semi-)automatically from its SIGCHLD handler.

Implementing this the obvious way, that's, doing the exec() call from
the first child process, would force us to introduce a more complex way
to reap qemu-ga's children. Like registering PIDs to be reaped and
having a way to wait for them when returning their exit status to
qemu-ga is necessary. The approach explained above avoids that complexity.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
 qapi-schema-guest.json |   24 ++++++
 qemu-ga.c              |   19 +++++-
 qga/commands-posix.c   |  188 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 230 insertions(+), 1 deletions(-)

diff --git a/qapi-schema-guest.json b/qapi-schema-guest.json
index 706925d..f4e0e1d 100644
--- a/qapi-schema-guest.json
+++ b/qapi-schema-guest.json
@@ -295,3 +295,27 @@
 ##
 { 'command': 'guest-fsfreeze-thaw',
   'returns': 'int' }
+
+##
+# @guest-suspend-disk
+#
+# Suspend guest to disk.
+#
+# This command tries to execute the scripts provided by the pm-utils package.
+# If it's not available, the suspend operation will be performed by manually
+# writing to a sysfs file.
+#
+# For the best results it's strongly recommended to have the pm-utils
+# package installed in the guest.
+#
+# Returns: nothing on success
+#          If suspend to disk is not supported, Unsupported
+#
+# Notes: o This is an asynchronous request. There's no guarantee a response
+#          will be sent
+#        o It's strongly recommended to issue the guest-sync command before
+#          sending commands when the guest resumes
+#
+# Since: 1.1
+##
+{ 'command': 'guest-suspend-disk' }
diff --git a/qemu-ga.c b/qemu-ga.c
index ba355d8..1c90e6e 100644
--- a/qemu-ga.c
+++ b/qemu-ga.c
@@ -17,6 +17,7 @@
 #include <getopt.h>
 #ifndef _WIN32
 #include <syslog.h>
+#include <sys/wait.h>
 #endif
 #include "json-streamer.h"
 #include "json-parser.h"
@@ -73,9 +74,16 @@ static void quit_handler(int sig)
 }
 
 #ifndef _WIN32
+/* reap _all_ terminated children */
+static void child_handler(int sig)
+{
+    int status;
+    while (waitpid(-1, &status, WNOHANG) > 0) /* NOTHING */;
+}
+
 static gboolean register_signal_handlers(void)
 {
-    struct sigaction sigact;
+    struct sigaction sigact, sigact_chld;
     int ret;
 
     memset(&sigact, 0, sizeof(struct sigaction));
@@ -91,6 +99,15 @@ static gboolean register_signal_handlers(void)
         g_error("error configuring signal handler: %s", strerror(errno));
         return false;
     }
+
+    memset(&sigact_chld, 0, sizeof(struct sigaction));
+    sigact_chld.sa_handler = child_handler;
+    sigact_chld.sa_flags = SA_NOCLDSTOP;
+    ret = sigaction(SIGCHLD, &sigact_chld, NULL);
+    if (ret == -1) {
+        g_error("error configuring signal handler: %s", strerror(errno));
+    }
+
     return true;
 }
 #endif
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 126127a..af785f5 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -23,6 +23,7 @@
 
 #include <sys/types.h>
 #include <sys/ioctl.h>
+#include <sys/wait.h>
 #include "qga/guest-agent-core.h"
 #include "qga-qmp-commands.h"
 #include "qerror.h"
@@ -30,6 +31,22 @@
 
 static GAState *ga_state;
 
+static void reopen_fd_to_null(int fd)
+{
+    int nullfd;
+
+    nullfd = open("/dev/null", O_RDWR);
+    if (nullfd < 0) {
+        return;
+    }
+
+    dup2(nullfd, fd);
+
+    if (nullfd != fd) {
+        close(nullfd);
+    }
+}
+
 void qmp_guest_shutdown(bool has_mode, const char *mode, Error **err)
 {
     int ret;
@@ -517,6 +534,177 @@ int64_t qmp_guest_fsfreeze_thaw(Error **err)
 }
 #endif
 
+#define LINUX_SYS_STATE_FILE "/sys/power/state"
+#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;
+    }
+
+    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);
+
+        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);
+            }
+
+            ret = read(fd, buf, sizeof(buf)-1);
+            if (ret <= 0) {
+                _exit(SUSPEND_NOT_SUPPORTED);
+            }
+            buf[ret] = '\0';
+
+            if (strstr(buf, sysfile_str)) {
+                _exit(SUSPEND_SUPPORTED);
+            }
+
+            _exit(SUSPEND_NOT_SUPPORTED);
+        }
+
+        if (pid > 0) {
+            wait(&status);
+        } else {
+            status = SUSPEND_NOT_SUPPORTED;
+        }
+
+        ret = write(pipefds[1], &status, sizeof(status));
+        if (ret != sizeof(status)) {
+            _exit(EXIT_FAILURE);
+        }
+
+        _exit(EXIT_SUCCESS);
+    }
+
+    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;
+    }
+
+    error_set(err, QERR_UNSUPPORTED);
+
+out:
+    close(pipefds[0]);
+}
+
+static void guest_suspend(const char *pmutils_bin, const char *sysfile_str,
+                          Error **err)
+{
+    pid_t pid;
+    char *pmutils_path;
+
+    pmutils_path = g_find_program_in_path(pmutils_bin);
+
+    pid = fork();
+    if (pid == 0) {
+        /* child */
+        int fd;
+
+        setsid();
+        reopen_fd_to_null(0);
+        reopen_fd_to_null(1);
+        reopen_fd_to_null(2);
+
+        if (pmutils_path) {
+            execle(pmutils_path, pmutils_bin, 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(EXIT_FAILURE);
+        }
+
+        fd = open(LINUX_SYS_STATE_FILE, O_WRONLY);
+        if (fd < 0) {
+            _exit(EXIT_FAILURE);
+        }
+
+        if (write(fd, sysfile_str, strlen(sysfile_str)) < 0) {
+            _exit(EXIT_FAILURE);
+        }
+
+        _exit(EXIT_SUCCESS);
+    }
+
+    g_free(pmutils_path);
+
+    if (pid < 0) {
+        error_set(err, QERR_UNDEFINED_ERROR);
+        return;
+    }
+}
+
+void qmp_guest_suspend_disk(Error **err)
+{
+    bios_supports_mode("pm-is-supported", "--hibernate", "disk", err);
+    if (error_is_set(err)) {
+        return;
+    }
+
+    guest_suspend("pm-hibernate", "disk", err);
+}
+
 /* register init/cleanup routines for stateful command groups */
 void ga_command_state_init(GAState *s, GACommandState *cs)
 {
-- 
1.7.9.111.gf3fb0.dirty