[Qemu-devel] [PATCH v3 0/2] qemu-ga: add hook to quiesce the guest on fsfreeze-freeze/thaw

[Qemu-devel] [PATCH v3 0/2] qemu-ga: add hook to quiesce the guest on fsfreeze-freeze/thaw

[Tomoki Sekiyama]

Hi,

This is version 3 of the qemu-ga fsfreeze hook patchset.

*Changes from v2: ( https://lists.gnu.org/archive/html/qemu-devel/2012-11/msg00918.html )
  1/2: Not changed.
  2/2: fsfreeze-hook:  Fixed typo.
       mysql-flush.sh: Use printf instead of echo to make it portable

---

Tomoki Sekiyama (2):
      qemu-ga: execute hook to quiesce the guest on fsfreeze-freeze/thaw
      qemu-ga: sample fsfreeze hooks


 docs/qemu-guest-agent/fsfreeze-hook                |   31 +++++++++++++
 .../fsfreeze-hook.d.sample/mysql-flush.sh          |   47 ++++++++++++++++++++
 qemu-ga.c                                          |   42 +++++++++++++++++-
 qga/commands-posix.c                               |   44 +++++++++++++++++++
 qga/guest-agent-core.h                             |    1 
 5 files changed, 164 insertions(+), 1 deletion(-)
 create mode 100755 docs/qemu-guest-agent/fsfreeze-hook
 create mode 100755 docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh


Thanks,
-- 
Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory

Re: [Qemu-devel] [PATCH v3 1/2] qemu-ga: execute hook to quiesce the guest on fsfreeze-freeze/thaw

[Tomoki Sekiyama]

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

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
---
 qemu-ga.c              |   42 +++++++++++++++++++++++++++++++++++++++++-
 qga/commands-posix.c   |   44 ++++++++++++++++++++++++++++++++++++++++++++
 qga/guest-agent-core.h |    1 +
 3 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/qemu-ga.c b/qemu-ga.c
index 9b59a52..d1d9b89 100644
--- a/qemu-ga.c
+++ b/qemu-ga.c
@@ -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_HOOK_DEFAULT CONFIG_QEMU_CONFDIR "/fsfreeze-hook"
+#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_hook;
+#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_hook\n"
+"                    specify fsfreeze hook (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 <mdroth@linux.vnet.ibm.com>\n"
     , cmd, QEMU_VERSION, QGA_VIRTIO_PATH_DEFAULT, QGA_PIDFILE_DEFAULT,
+#ifdef CONFIG_FSFREEZE
+    QGA_FSFREEZE_HOOK_DEFAULT,
+#endif
     QGA_STATEDIR_DEFAULT);
 }
 
@@ -401,6 +420,13 @@ void ga_unset_frozen(GAState *s)
     }
 }
 
+#ifdef CONFIG_FSFREEZE
+const char *ga_fsfreeze_hook(GAState *s)
+{
+    return s->fsfreeze_hook;
+}
+#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_hook = QGA_FSFREEZE_HOOK_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-hook", 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_hook = 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_hook = fsfreeze_hook;
+#endif
     g_log_set_default_handler(ga_log, s);
     g_log_set_fatal_mask(NULL, G_LOG_LEVEL_ERROR);
     ga_enable_logging(s);
diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 726930a..8c3e341 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -396,6 +396,45 @@ GuestFsfreezeStatus qmp_guest_fsfreeze_status(Error **err)
     return GUEST_FSFREEZE_STATUS_THAWED;
 }
 
+static void execute_fsfreeze_hook(const char *arg)
+{
+    int status;
+    pid_t pid, rpid;
+    const char *hook;
+
+    hook = ga_fsfreeze_hook(ga_state);
+    if (!hook || access(hook, X_OK) != 0) {
+        return;
+    }
+
+    slog("executing fsfreeze hook with arg `%s'", arg);
+    pid = fork();
+    if (pid == 0) {
+        setsid();
+        reopen_fd_to_null(0);
+        reopen_fd_to_null(1);
+        reopen_fd_to_null(2);
+
+        execle(hook, hook, arg, NULL, environ);
+        _exit(EXIT_FAILURE);
+    } else if (pid < 0) {
+        slog("execution of fsfreeze hook failed: %s", strerror(errno));
+        return;
+    }
+
+    do {
+        rpid = waitpid(pid, &status, 0);
+    } while (rpid == -1 && errno == EINTR);
+    if (rpid == pid && WIFEXITED(status)) {
+        int st = WEXITSTATUS(status);
+        if (st) {
+            slog("fsfreeze hook failed with status %d", st);
+        }
+    } else if (rpid == pid && WIFSIGNALED(status)) {
+        slog("fsfreeze hook killed by signal %d", WTERMSIG(status));
+    }
+}
+
 /*
  * Walk list of mounted file systems in the guest, and freeze the ones which
  * are real local file systems.
@@ -410,6 +449,8 @@ int64_t qmp_guest_fsfreeze_freeze(Error **err)
 
     slog("guest-fsfreeze called");
 
+    execute_fsfreeze_hook("freeze");
+
     QTAILQ_INIT(&mounts);
     ret = build_fs_mount_list(&mounts);
     if (ret < 0) {
@@ -513,6 +554,9 @@ int64_t qmp_guest_fsfreeze_thaw(Error **err)
 
     ga_unset_frozen(ga_state);
     free_fs_mount_list(&mounts);
+
+    execute_fsfreeze_hook("thaw");
+
     return i;
 }
 
diff --git a/qga/guest-agent-core.h b/qga/guest-agent-core.h
index 49a7abe..c6e8de0 100644
--- a/qga/guest-agent-core.h
+++ b/qga/guest-agent-core.h
@@ -34,6 +34,7 @@ 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_hook(GAState *s);
 
 #ifndef _WIN32
 void reopen_fd_to_null(int fd);

Re: [Qemu-devel] [PATCH v3 2/2] qemu-ga: sample fsfreeze hooks

[Tomoki Sekiyama]

Adds sample hook scripts for --fsfreeze-hook option of qemu-ga.
  - fsfreeze-hook : execute scripts in fsfreeze-hook.d/
  - fsfreeze-hook.d.sample/mysql-flush.sh : quiesce MySQL before snapshot

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
---
 docs/qemu-guest-agent/fsfreeze-hook                |   31 +++++++++++++
 .../fsfreeze-hook.d.sample/mysql-flush.sh          |   47 ++++++++++++++++++++
 2 files changed, 78 insertions(+)
 create mode 100755 docs/qemu-guest-agent/fsfreeze-hook
 create mode 100755 docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh

diff --git a/docs/qemu-guest-agent/fsfreeze-hook b/docs/qemu-guest-agent/fsfreeze-hook
new file mode 100755
index 0000000..319f68c
--- /dev/null
+++ b/docs/qemu-guest-agent/fsfreeze-hook
@@ -0,0 +1,31 @@
+#!/bin/sh
+
+# This script is executed when a guest agent receives fsfreeze-freeze and
+# fsfreeze-thaw command, if it is specified in --fsfreeze-hook (-F)
+# option of qemu-ga or placed in default path (/etc/qemu/fsfreeze-hook).
+# When the agent receives fsfreeze-freeze request, this script is issued with
+# "freeze" argument before the filesystem is freezed. And for fsfreeze-thaw
+# request, it is issued with "thaw" argument after filesystem is thawed.
+
+LOGFILE=/var/log/qga-fsfreeze-hook.log
+FSFREEZE_D=$(dirname -- "$0")/fsfreeze-hook.d
+
+# Check whether file $1 is a backup or rpm-generated file and should be ignored
+is_ignored_file() {
+    case "$1" in
+        *~ | *.bak | *.orig | *.rpmnew | *.rpmorig | *.rpmsave)
+            return 0 ;;
+    esac
+    return 1
+}
+
+# Iterate executables in directory "fsfreeze-hook.d" with the specified args
+[ ! -d "$FSFREEZE_D" ] && exit 1
+for file in "$FSFREEZE_D"/* ; do
+    is_ignored_file "$file" && continue
+    [ -x "$file" ] || continue
+    echo "$(date): execute $file $@" >>$LOGFILE
+    "$file" "$@" >>$LOGFILE 2>&1
+    STATUS=$?
+    echo "$(date): $file finished with status=$STATUS" >>$LOGFILE
+done
diff --git a/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh b/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh
new file mode 100755
index 0000000..e6d7998
--- /dev/null
+++ b/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh
@@ -0,0 +1,47 @@
+#!/bin/sh
+
+# Flush MySQL tables to the disk before the filesystem is freezed.
+# At the same time, this keeps a read lock while the filesystem is freezed
+# in order to avoid write accesses by the other clients.
+
+MYSQL="mysql -uroot" #"-prootpassword"
+FIFO=/tmp/mysql-flush.fifo
+
+flush_and_wait() {
+    printf "FLUSH TABLES WITH READ LOCK \\G\n"
+    read < $FIFO
+    printf "UNLOCK TABLES \\G\n"
+}
+
+case "$1" in
+    freeze)
+        mkfifo $FIFO || exit 1
+        flush_and_wait | $MYSQL &
+        # wait until every block is flushed
+        while [ "$(echo 'SHOW STATUS LIKE "Key_blocks_not_flushed"' |\
+                 $MYSQL | tail -1 | cut -f 2)" -gt 0 ]; do
+            sleep 1
+        done
+        # for InnoDB, wait until every log is flushed
+        INNODB_STATUS=$(mktemp /tmp/mysql-flush.XXXXXX)
+        [ $? -ne 0 ] && exit 2
+        trap "rm -f $INNODB_STATUS" SIGINT
+        while :; do
+            printf "SHOW ENGINE INNODB STATUS \\G" | $MYSQL > $INNODB_STATUS
+            LOG_CURRENT=$(grep 'Log sequence number' $INNODB_STATUS |\
+                          tr -s ' ' | cut -d' ' -f4)
+            LOG_FLUSHED=$(grep 'Log flushed up to' $INNODB_STATUS |\
+                          tr -s ' ' | cut -d' ' -f5)
+            [ "$LOG_CURRENT" = "$LOG_FLUSHED" ] && break
+            sleep 1
+        done
+        rm -f $INNODB_STATUS
+        ;;
+
+    thaw)
+        [ ! -p $FIFO ] && exit 1
+        echo > $FIFO
+        rm -f $FIFO
+        ;;
+esac
+

Re: [Qemu-devel] [PATCH v3 1/2] qemu-ga: execute hook to quiesce the guest on fsfreeze-freeze/thaw

[mdroth]

On Tue, Nov 13, 2012 at 01:56:56PM +0900, Tomoki Sekiyama wrote:
> 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 hook script
> specified in --fsfreeze-hook option is executed with "freeze" argument
> before the filesystem is frozen. For fsfreeze-thaw command, the hook
> script is executed with "thaw" argument after the filesystem is thawed.
> 
> Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
> ---
>  qemu-ga.c              |   42 +++++++++++++++++++++++++++++++++++++++++-
>  qga/commands-posix.c   |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  qga/guest-agent-core.h |    1 +
>  3 files changed, 86 insertions(+), 1 deletion(-)
> 
> diff --git a/qemu-ga.c b/qemu-ga.c
> index 9b59a52..d1d9b89 100644
> --- a/qemu-ga.c
> +++ b/qemu-ga.c
> @@ -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_HOOK_DEFAULT CONFIG_QEMU_CONFDIR "/fsfreeze-hook"
> +#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_hook;
> +#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_hook\n"

Small nit, but can we change this to --fsfreeze-hook?

> +"                    specify fsfreeze hook (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 <mdroth@linux.vnet.ibm.com>\n"
>      , cmd, QEMU_VERSION, QGA_VIRTIO_PATH_DEFAULT, QGA_PIDFILE_DEFAULT,
> +#ifdef CONFIG_FSFREEZE
> +    QGA_FSFREEZE_HOOK_DEFAULT,
> +#endif
>      QGA_STATEDIR_DEFAULT);
>  }
> 
> @@ -401,6 +420,13 @@ void ga_unset_frozen(GAState *s)
>      }
>  }
> 
> +#ifdef CONFIG_FSFREEZE
> +const char *ga_fsfreeze_hook(GAState *s)
> +{
> +    return s->fsfreeze_hook;
> +}
> +#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_hook = QGA_FSFREEZE_HOOK_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-hook", 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_hook = 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_hook = fsfreeze_hook;
> +#endif
>      g_log_set_default_handler(ga_log, s);
>      g_log_set_fatal_mask(NULL, G_LOG_LEVEL_ERROR);
>      ga_enable_logging(s);
> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
> index 726930a..8c3e341 100644
> --- a/qga/commands-posix.c
> +++ b/qga/commands-posix.c
> @@ -396,6 +396,45 @@ GuestFsfreezeStatus qmp_guest_fsfreeze_status(Error **err)
>      return GUEST_FSFREEZE_STATUS_THAWED;
>  }
> 

Rather than passing freeze/thaw in as a string, I think an enum
parameter of the form:

typedef enum {
    FSFREEZE_HOOK_THAW,    
    FSFREEZE_HOOK_FREEZE,    
} FsfreezeHook;

would be better in terms of documenting the interface.

> +static void execute_fsfreeze_hook(const char *arg)
> +{
> +    int status;
> +    pid_t pid, rpid;
> +    const char *hook;
> +
> +    hook = ga_fsfreeze_hook(ga_state);
> +    if (!hook || access(hook, X_OK) != 0) {
> +        return;
> +    }
> +
> +    slog("executing fsfreeze hook with arg `%s'", arg);
> +    pid = fork();
> +    if (pid == 0) {
> +        setsid();
> +        reopen_fd_to_null(0);
> +        reopen_fd_to_null(1);
> +        reopen_fd_to_null(2);
> +
> +        execle(hook, hook, arg, NULL, environ);
> +        _exit(EXIT_FAILURE);
> +    } else if (pid < 0) {
> +        slog("execution of fsfreeze hook failed: %s", strerror(errno));
> +        return;
> +    }
> +
> +    do {
> +        rpid = waitpid(pid, &status, 0);
> +    } while (rpid == -1 && errno == EINTR);
> +    if (rpid == pid && WIFEXITED(status)) {
> +        int st = WEXITSTATUS(status);
> +        if (st) {
> +            slog("fsfreeze hook failed with status %d", st);
> +        }
> +    } else if (rpid == pid && WIFSIGNALED(status)) {
> +        slog("fsfreeze hook killed by signal %d", WTERMSIG(status));
> +    }
> +}
> +
>  /*
>   * Walk list of mounted file systems in the guest, and freeze the ones which
>   * are real local file systems.
> @@ -410,6 +449,8 @@ int64_t qmp_guest_fsfreeze_freeze(Error **err)
> 
>      slog("guest-fsfreeze called");
> 
> +    execute_fsfreeze_hook("freeze");
> +

I think if a user configures a pre-freeze hook, it's failure should be
treated as a failure of the fsfreeze call in general, otherwise we risk
moving forward based on false assumptions that can lead to data loss or
other issues. I think the thaw hook is okay the way it is though, they
can review the logs for any issues arising after the VM is
unfrozen.

>      QTAILQ_INIT(&mounts);
>      ret = build_fs_mount_list(&mounts);
>      if (ret < 0) {
> @@ -513,6 +554,9 @@ int64_t qmp_guest_fsfreeze_thaw(Error **err)
> 
>      ga_unset_frozen(ga_state);
>      free_fs_mount_list(&mounts);
> +
> +    execute_fsfreeze_hook("thaw");
> +
>      return i;
>  }
> 
> diff --git a/qga/guest-agent-core.h b/qga/guest-agent-core.h
> index 49a7abe..c6e8de0 100644
> --- a/qga/guest-agent-core.h
> +++ b/qga/guest-agent-core.h
> @@ -34,6 +34,7 @@ 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_hook(GAState *s);
> 
>  #ifndef _WIN32
>  void reopen_fd_to_null(int fd);
> 

Re: [Qemu-devel] [PATCH v3 2/2] qemu-ga: sample fsfreeze hooks

[mdroth]

On Tue, Nov 13, 2012 at 01:56:59PM +0900, Tomoki Sekiyama wrote:
> Adds sample hook scripts for --fsfreeze-hook option of qemu-ga.
>   - fsfreeze-hook : execute scripts in fsfreeze-hook.d/
>   - fsfreeze-hook.d.sample/mysql-flush.sh : quiesce MySQL before snapshot
> 
> Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>

Reviewed-by: Michael Roth <mdroth@linux.vnet.ibm.com>

> ---
>  docs/qemu-guest-agent/fsfreeze-hook                |   31 +++++++++++++
>  .../fsfreeze-hook.d.sample/mysql-flush.sh          |   47 ++++++++++++++++++++
>  2 files changed, 78 insertions(+)
>  create mode 100755 docs/qemu-guest-agent/fsfreeze-hook
>  create mode 100755 docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh
> 
> diff --git a/docs/qemu-guest-agent/fsfreeze-hook b/docs/qemu-guest-agent/fsfreeze-hook
> new file mode 100755
> index 0000000..319f68c
> --- /dev/null
> +++ b/docs/qemu-guest-agent/fsfreeze-hook
> @@ -0,0 +1,31 @@
> +#!/bin/sh
> +
> +# This script is executed when a guest agent receives fsfreeze-freeze and
> +# fsfreeze-thaw command, if it is specified in --fsfreeze-hook (-F)
> +# option of qemu-ga or placed in default path (/etc/qemu/fsfreeze-hook).
> +# When the agent receives fsfreeze-freeze request, this script is issued with
> +# "freeze" argument before the filesystem is freezed. And for fsfreeze-thaw
> +# request, it is issued with "thaw" argument after filesystem is thawed.
> +
> +LOGFILE=/var/log/qga-fsfreeze-hook.log
> +FSFREEZE_D=$(dirname -- "$0")/fsfreeze-hook.d
> +
> +# Check whether file $1 is a backup or rpm-generated file and should be ignored
> +is_ignored_file() {
> +    case "$1" in
> +        *~ | *.bak | *.orig | *.rpmnew | *.rpmorig | *.rpmsave)
> +            return 0 ;;
> +    esac
> +    return 1
> +}
> +
> +# Iterate executables in directory "fsfreeze-hook.d" with the specified args
> +[ ! -d "$FSFREEZE_D" ] && exit 1
> +for file in "$FSFREEZE_D"/* ; do
> +    is_ignored_file "$file" && continue
> +    [ -x "$file" ] || continue
> +    echo "$(date): execute $file $@" >>$LOGFILE
> +    "$file" "$@" >>$LOGFILE 2>&1
> +    STATUS=$?
> +    echo "$(date): $file finished with status=$STATUS" >>$LOGFILE
> +done
> diff --git a/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh b/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh
> new file mode 100755
> index 0000000..e6d7998
> --- /dev/null
> +++ b/docs/qemu-guest-agent/fsfreeze-hook.d.sample/mysql-flush.sh
> @@ -0,0 +1,47 @@
> +#!/bin/sh
> +
> +# Flush MySQL tables to the disk before the filesystem is freezed.
> +# At the same time, this keeps a read lock while the filesystem is freezed
> +# in order to avoid write accesses by the other clients.
> +
> +MYSQL="mysql -uroot" #"-prootpassword"
> +FIFO=/tmp/mysql-flush.fifo
> +
> +flush_and_wait() {
> +    printf "FLUSH TABLES WITH READ LOCK \\G\n"
> +    read < $FIFO
> +    printf "UNLOCK TABLES \\G\n"
> +}
> +
> +case "$1" in
> +    freeze)
> +        mkfifo $FIFO || exit 1
> +        flush_and_wait | $MYSQL &
> +        # wait until every block is flushed
> +        while [ "$(echo 'SHOW STATUS LIKE "Key_blocks_not_flushed"' |\
> +                 $MYSQL | tail -1 | cut -f 2)" -gt 0 ]; do
> +            sleep 1
> +        done
> +        # for InnoDB, wait until every log is flushed
> +        INNODB_STATUS=$(mktemp /tmp/mysql-flush.XXXXXX)
> +        [ $? -ne 0 ] && exit 2
> +        trap "rm -f $INNODB_STATUS" SIGINT
> +        while :; do
> +            printf "SHOW ENGINE INNODB STATUS \\G" | $MYSQL > $INNODB_STATUS
> +            LOG_CURRENT=$(grep 'Log sequence number' $INNODB_STATUS |\
> +                          tr -s ' ' | cut -d' ' -f4)
> +            LOG_FLUSHED=$(grep 'Log flushed up to' $INNODB_STATUS |\
> +                          tr -s ' ' | cut -d' ' -f5)
> +            [ "$LOG_CURRENT" = "$LOG_FLUSHED" ] && break
> +            sleep 1
> +        done
> +        rm -f $INNODB_STATUS
> +        ;;
> +
> +    thaw)
> +        [ ! -p $FIFO ] && exit 1
> +        echo > $FIFO
> +        rm -f $FIFO
> +        ;;
> +esac
> +
> 

Re: [Qemu-devel] [PATCH v3 1/2] qemu-ga: execute hook to quiesce the guest on fsfreeze-freeze/thaw

[Tomoki Sekiyama]

Hi Michael,

Thanks for your review.

On 2012/11/21 6:00, mdroth wrote:
> On Tue, Nov 13, 2012 at 01:56:56PM +0900, Tomoki Sekiyama wrote:
>> 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 hook script
>> specified in --fsfreeze-hook option is executed with "freeze" argument
>> before the filesystem is frozen. For fsfreeze-thaw command, the hook
>> script is executed with "thaw" argument after the filesystem is thawed.
>>
>> Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
>> ---
<snip>
>>  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_hook\n"
> 
> Small nit, but can we change this to --fsfreeze-hook?

Ah, sure.

>> diff --git a/qga/commands-posix.c b/qga/commands-posix.c
>> index 726930a..8c3e341 100644
>> --- a/qga/commands-posix.c
>> +++ b/qga/commands-posix.c
>> @@ -396,6 +396,45 @@ GuestFsfreezeStatus qmp_guest_fsfreeze_status(Error **err)
>>      return GUEST_FSFREEZE_STATUS_THAWED;
>>  }
>>
> 
> Rather than passing freeze/thaw in as a string, I think an enum
> parameter of the form:
> 
> typedef enum {
>     FSFREEZE_HOOK_THAW,    
>     FSFREEZE_HOOK_FREEZE,    
> } FsfreezeHook;
> 
> would be better in terms of documenting the interface.

Okey, I will use enum as the argument.

>> +static void execute_fsfreeze_hook(const char *arg)
<snip>
>>  /*
>>   * Walk list of mounted file systems in the guest, and freeze the ones which
>>   * are real local file systems.
>> @@ -410,6 +449,8 @@ int64_t qmp_guest_fsfreeze_freeze(Error **err)
>>
>>      slog("guest-fsfreeze called");
>>
>> +    execute_fsfreeze_hook("freeze");
>> +
> 
> I think if a user configures a pre-freeze hook, it's failure should be
> treated as a failure of the fsfreeze call in general, otherwise we risk
> moving forward based on false assumptions that can lead to data loss or
> other issues. I think the thaw hook is okay the way it is though, they
> can review the logs for any issues arising after the VM is
> unfrozen.

I think that is reasonable. It would be better to notify the failure of
fsfreeze hook to the host side for investigation of the issue.

I will fix these in the next patchset.

Thanks,
-- 
Tomoki Sekiyama <tomoki.sekiyama.qu@hitachi.com>
Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory