qemu-ga: execute script to quiesce the guest on fsfreeze-freeze/thaw

To use the online disk snapshot for online-backup, application-level consistency of the snapshot image is required. However, currently the guest agent can provide only filesystem-level consistency, and the snapshot may contain dirty data, for example, incomplete transactions. This patch provides the opportunity to quiesce applications before snapshot is taken.

When the qemu-ga receives fsfreeze-freeze command, the script specified in --fsfreeze-script option is executed with "freeze" argument before the filesystem is frozen. For fsfreeze-thaw command, the script is executed with "thaw" argument after the filesystem is thawed.

Signed-off-by Tomoki Sekiyama <[email protected]>

---
  qemu-ga.c              | 42 +++++++++++++++++++++++++++++++++++++++++-
  qga/commands-posix.c   | 34 ++++++++++++++++++++++++++++++++++
  qga/guest-agent-core.h |  2 ++
  3 files changed, 77 insertions(+), 1 deletion(-)

qemu-ga.c +41 -1

index 9b59a52..7cb682e 100644
@@ -34,6 +34,12 @@
  #include "qga/service-win32.h"
  #include <windows.h>
  #endif
+#ifdef __linux__
+#include <linux/fs.h>
+#ifdef FIFREEZE
+#define CONFIG_FSFREEZE
+#endif
+#endif
 
  #ifndef _WIN32
  #define QGA_VIRTIO_PATH_DEFAULT "/dev/virtio-ports/org.qemu.guest_agent.0"

@@ -42,6 +48,9 @@
  #endif
  #define QGA_STATEDIR_DEFAULT CONFIG_QEMU_LOCALSTATEDIR "/run"
  #define QGA_PIDFILE_DEFAULT QGA_STATEDIR_DEFAULT "/qemu-ga.pid"
+#ifdef CONFIG_FSFREEZE
+#define QGA_FSFREEZE_SCRIPT_DEFAULT CONFIG_QEMU_CONFDIR "/fsfreeze.sh"
+#endif
  #define QGA_SENTINEL_BYTE 0xFF
 
  struct GAState {

@@ -64,6 +73,9 @@ struct GAState {
          const char *log_filepath;
          const char *pid_filepath;
      } deferred_options;
+#ifdef CONFIG_FSFREEZE
+    const char *fsfreeze_script;
+#endif
  };
 
  struct GAState *ga_state;

@@ -153,6 +165,10 @@ static void usage(const char *cmd)
  "                    %s)\n"
  "  -l, --logfile     set logfile path, logs to stderr by default\n"
  "  -f, --pidfile     specify pidfile (default is %s)\n"
+#ifdef CONFIG_FSFREEZE
+"  -F, --fsfreeze_script\n"
+"                    specify fsfreeze script (default is %s)\n"
+#endif
  "  -t, --statedir    specify dir to store state information (absolute paths\n"
  "                    only, default is %s)\n"
  "  -v, --verbose     log extra debugging information\n"

@@ -167,6 +183,9 @@ static void usage(const char *cmd)
  "\n"
  "Report bugs to <[email protected]>\n"
      , cmd, QEMU_VERSION, QGA_VIRTIO_PATH_DEFAULT, QGA_PIDFILE_DEFAULT,
+#ifdef CONFIG_FSFREEZE
+    QGA_FSFREEZE_SCRIPT_DEFAULT,
+#endif
      QGA_STATEDIR_DEFAULT);
  }
 

@@ -401,6 +420,13 @@ void ga_unset_frozen(GAState *s)
      }
  }
 
+#ifdef CONFIG_FSFREEZE
+const char *ga_fsfreeze_script(GAState *s)
+{
+    return s->fsfreeze_script;
+}
+#endif
+
  static void become_daemon(const char *pidfile)
  {
  #ifndef _WIN32

@@ -678,10 +704,13 @@ VOID WINAPI service_main(DWORD argc, TCHAR *argv[])
 
  int main(int argc, char **argv)
  {
-    const char *sopt = "hVvdm:p:l:f:b:s:t:";
+    const char *sopt = "hVvdm:p:l:f:F:b:s:t:";
      const char *method = NULL, *path = NULL;
      const char *log_filepath = NULL;
      const char *pid_filepath = QGA_PIDFILE_DEFAULT;
+#ifdef CONFIG_FSFREEZE
+    const char *fsfreeze_script = QGA_FSFREEZE_SCRIPT_DEFAULT;
+#endif
      const char *state_dir = QGA_STATEDIR_DEFAULT;
  #ifdef _WIN32
      const char *service = NULL;

@@ -691,6 +720,9 @@ int main(int argc, char **argv)
          { "version", 0, NULL, 'V' },
          { "logfile", 1, NULL, 'l' },
          { "pidfile", 1, NULL, 'f' },
+#ifdef CONFIG_FSFREEZE
+        { "fsfreeze-script", 1, NULL, 'F' },
+#endif
          { "verbose", 0, NULL, 'v' },
          { "method", 1, NULL, 'm' },
          { "path", 1, NULL, 'p' },

@@ -723,6 +755,11 @@ int main(int argc, char **argv)
          case 'f':
              pid_filepath = optarg;
              break;
+#ifdef CONFIG_FSFREEZE
+        case 'F':
+            fsfreeze_script = optarg;
+            break;
+#endif
          case 't':
               state_dir = optarg;
               break;

@@ -786,6 +823,9 @@ int main(int argc, char **argv)
      s = g_malloc0(sizeof(GAState));
      s->log_level = log_level;
      s->log_file = stderr;
+#ifdef CONFIG_FSFREEZE
+    s->fsfreeze_script = fsfreeze_script;
+#endif
      g_log_set_default_handler(ga_log, s);
      g_log_set_fatal_mask(NULL, G_LOG_LEVEL_ERROR);
      ga_enable_logging(s);

qga/commands-posix.c +34 -0

index 726930a..007c0a3 100644
@@ -13,6 +13,7 @@
 
  #include <glib.h>
  #include <sys/types.h>
+#include <sys/stat.h>
  #include <sys/ioctl.h>
  #include <sys/wait.h>
  #include "qga/guest-agent-core.h"

@@ -396,6 +397,34 @@ GuestFsfreezeStatus qmp_guest_fsfreeze_status(Error **err)
      return GUEST_FSFREEZE_STATUS_THAWED;
  }
 
+int execute_fsfreeze_script(const char *arg)
+{
+    int ret = -1;
+    const char *fsfreeze_script;
+    char *cmdline;
+    struct stat st;
+
+    fsfreeze_script = ga_fsfreeze_script(ga_state);
+    if (fsfreeze_script && stat(fsfreeze_script, &st) == 0) {
+        if (S_ISREG(st.st_mode) && (st.st_mode & S_IXUSR)) {
+            slog("executing fsfreeze script with arg `%s'", arg);
+            cmdline = malloc(strlen(fsfreeze_script) + strlen(arg) + 2);
+            if (cmdline) {
+                sprintf(cmdline, "%s %s", fsfreeze_script, arg);
+                ret = system(cmdline);
+                free(cmdline);
+            }
+            if (ret > 0) {
+                g_warning("fsfreeze script failed with status=%d", ret);
+            } else if (ret == -1) {
+                g_warning("execution of fsfreeze script failed: %s",
+                          strerror(errno));
+            }
+        }
+    }
+    return ret;
+}
+
  /*
   * Walk list of mounted file systems in the guest, and freeze the ones which
   * are real local file systems.

@@ -410,6 +439,8 @@ int64_t qmp_guest_fsfreeze_freeze(Error **err)
 
      slog("guest-fsfreeze called");
 
+    execute_fsfreeze_script("freeze");
+
      QTAILQ_INIT(&mounts);
      ret = build_fs_mount_list(&mounts);
      if (ret < 0) {

@@ -513,6 +544,9 @@ int64_t qmp_guest_fsfreeze_thaw(Error **err)
 
      ga_unset_frozen(ga_state);
      free_fs_mount_list(&mounts);
+
+    execute_fsfreeze_script("thaw");
+
      return i;
  }
 

qga/guest-agent-core.h +2 -0

index 49a7abe..b466bfd 100644
@@ -34,6 +34,8 @@ void ga_set_response_delimited(GAState *s);
  bool ga_is_frozen(GAState *s);
  void ga_set_frozen(GAState *s);
  void ga_unset_frozen(GAState *s);
+const char *ga_fsfreeze_script(GAState *s);
+int execute_fsfreeze_script(const char *arg);
 
  #ifndef _WIN32
  void reopen_fd_to_null(int fd);