Re: [PATCH sandbox 2/4] Sync and unmount filesystems during shutdown

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On Fri, 2015-09-04 at 12:40 +0100, Daniel P. Berrange wrote:
> To ensure that all pending I/O for filesytems backed by block
> devices is flushed to disk, it is important to sync and unmount
> the filesystems during shutdown. To avoid relying on the kernel
> reboot-on-panic behaviour, we also explicitly call reboot to
> power off the guest.
> 
> Signed-off-by: Daniel P. Berrange <berrange@xxxxxxxxxx>
> ---
>  libvirt-sandbox/libvirt-sandbox-init-common.c | 166 ++++++++++++++++++++++++++
>  libvirt-sandbox/libvirt-sandbox-init-qemu.c   |   1 +
>  2 files changed, 167 insertions(+)
> 
> diff --git a/libvirt-sandbox/libvirt-sandbox-init-common.c b/libvirt-sandbox/libvirt-sandbox-init-common.c
> index 760509f..a3b4687 100644
> --- a/libvirt-sandbox/libvirt-sandbox-init-common.c
> +++ b/libvirt-sandbox/libvirt-sandbox-init-common.c
> @@ -44,6 +44,8 @@
>  #include <unistd.h>
>  #include <limits.h>
>  #include <grp.h>
> +#include <mntent.h>
> +#include <sys/reboot.h>
>  
>  #include "libvirt-sandbox-rpcpacket.h"
>  
> @@ -52,6 +54,8 @@ static gboolean verbose = FALSE;
>  static int sigwrite;
>  
>  #define ATTR_UNUSED __attribute__((__unused__))
> +static void sync_data(void);
> +static void umount_fs(void);
>  
>  static void sig_child(int sig ATTR_UNUSED)
>  {
> @@ -598,6 +602,14 @@ static GVirSandboxRPCPacket *gvir_sandbox_encode_exit(int status,
>      pkt->header.type = GVIR_SANDBOX_PROTOCOL_TYPE_MESSAGE;
>      pkt->header.serial = serial;
>  
> +    /* The host may destroy the guest any time after receiving
> +     * the exit code messages. So although the main() has code
> +     * to sync + unmount we can't rely on that running. So we
> +     * opportunistically sync + unmount here too.
> +     */
> +    sync_data();
> +    umount_fs();
> +
>      if (!gvir_sandbox_rpcpacket_encode_header(pkt, error))
>          goto error;
>      if (!gvir_sandbox_rpcpacket_encode_payload_msg(pkt,
> @@ -613,7 +625,151 @@ static GVirSandboxRPCPacket *gvir_sandbox_encode_exit(int status,
>      return NULL;
>  }
>  
> +/* Copied & adapted from libguestfs daemon/sync.c under LGPLv2+ */
> +static void sync_data(void)
> +{
> +  DIR *dir;
> +  struct dirent *d;
> +  char *dev_path;
> +  int fd;
> +
> +  if (debug)
> +      fprintf(stderr, "Syncing data\n");
> +  sync();
> +
> +  /* On Linux, sync(2) doesn't perform a barrier, so qemu (which may
> +   * have a writeback cache, even with cache=none) will still have
> +   * some unwritten data.  Force the data out of any qemu caches, by
> +   * calling fsync on all block devices.  Note we still need the
> +   * call to sync above in order to schedule the writes.
> +   * Thanks to: Avi Kivity, Kevin Wolf.
> +   */
> +
> +  if (!(dir = opendir("/dev"))) {
> +      fprintf(stderr, "opendir: /dev failed %s\n", strerror(errno));
> +      return;
> +  }
> +
> +  for (;;) {
> +      errno = 0;
> +      d = readdir(dir);
> +      if (!d)
> +          break;
> +
> +      if (!(g_str_has_prefix(d->d_name, "sd") ||
> +            g_str_has_prefix(d->d_name, "hd") ||
> +            g_str_has_prefix(d->d_name, "ubd") ||
> +            g_str_has_prefix(d->d_name, "vd") ||
> +            g_str_has_prefix(d->d_name, "sr"))) {
> +          continue;
> +      }
> +
> +      dev_path = g_strdup_printf("/dev/%s", d->d_name);
> +
> +      if (debug)
> +          fprintf(stderr, "Syncing fd %s\n", dev_path);
> +      if ((fd = open(dev_path, O_RDONLY)) < 0) {
> +          fprintf(stderr, "cannot open %s: %s\n", dev_path,
> +                  strerror(errno));
> +          g_free(dev_path);
> +          continue;
> +      }
> +
> +      /* fsync the device. */
> +      if (debug) {
> +          fprintf(stderr, "fsync %s\n", dev_path);
> +      }
> +
> +      if (fsync(fd) < 0) {
> +          fprintf(stderr, "failed to fsync %s: %s\n",
> +                  dev_path, strerror(errno));
> +      }
> +      if (close(fd) < 0) {
> +          fprintf(stderr, "failed to close %s: %s\n",
> +                  dev_path, strerror(errno));
> +      }
> +      g_free(dev_path);
> +  }
> +
> +  /* Check readdir didn't fail */
> +  if (errno != 0) {
> +      fprintf(stderr, "Failed to read /dev: %s\n",
> +              strerror(errno));
> +  }
> +
> +  /* Close the directory handle */
> +  if (closedir(dir) < 0) {
> +      fprintf(stderr, "Failed to block /dev: %s\n",
> +              strerror(errno));
> +  }
> +
> +  if (debug)
> +      fprintf(stderr, "Syncing complete\n");
> +}
> +
> +
> +static int
> +compare_longest_first (gconstpointer vp1, gconstpointer vp2)
> +{
> +    int n1 = strlen(vp1);
> +    int n2 = strlen(vp2);
> +    return n2 - n1;
> +}
> +
> +
> +/* Copied & adapted from libguestfs daemon/sync.c under LGPLv2+ */
> +static void umount_fs(void)
> +{
> +    FILE *fp;
> +    struct mntent *m;
> +    GList *mounts = NULL, *tmp;
> +
> +    if (debug)
> +        fprintf(stderr, "Unmounting all filesystems\n");
> +    if (!(fp = setmntent ("/proc/mounts", "r"))) {
> +        fprintf(stderr, "Failed to open /proc/mounts: %s\n",
> +                strerror(errno));
> +        return;
> +    }
> +
> +    while ((m = getmntent (fp)) != NULL) {
> +        if (debug)
> +            fprintf(stderr, "Got fsname=%s dir=%s type=%s opts=%s freq=%d passno=%d\n",
> +                    m->mnt_fsname, m->mnt_dir, m->mnt_type, m->mnt_opts,
> +                    m->mnt_freq, m->mnt_passno);
> +
> +        mounts = g_list_append(mounts, g_strdup(m->mnt_dir));
> +    }
>  
> +    endmntent(fp);
> +
> +    mounts = g_list_sort(mounts, compare_longest_first);
> +
> +    /* Unmount them. */
> +    tmp = mounts;
> +    while (tmp) {
> +        char *dir = tmp->data;
> +
> +        if (debug)
> +            fprintf(stderr, "Unmounting %s\n", dir);
> +        if (umount(dir) < 0) {
> +            /* We expect some failures, so don't pollute
> +             * logs with them uneccessarily
> +             */
> +            if (debug || errno != EBUSY)
> +                fprintf(stderr, "cannot unmount %s: %s\n",
> +                        dir, strerror(errno));
> +            /* ignore failure */
> +        }
> +        g_free(dir);
> +
> +        tmp = tmp->next;
> +    }
> +
> +    g_list_free(mounts);
> +    if (debug)
> +        fprintf(stderr, "Unmounting complete\n");
> +}
>  
> 
>  static gssize read_data(int fd, char *buf, size_t len)
> @@ -1204,6 +1360,7 @@ static void libvirt_sandbox_version(void)
>  
>  int main(int argc, char **argv) {
>      gchar *configfile = NULL;
> +    gboolean poweroff = FALSE;
>      GError *error = NULL;
>      GOptionContext *context;
>      GOptionEntry options[] = {
> @@ -1215,6 +1372,8 @@ int main(int argc, char **argv) {
>            N_("display debugging information"), NULL },
>          { "config", 'c', 0, G_OPTION_ARG_STRING, &configfile,
>            N_("config file path"), "URI"},
> +        { "poweroff", 'p', 0, G_OPTION_ARG_NONE, &poweroff,
> +          N_("clean power off when exiting"), NULL},
>          { NULL, 0, 0, G_OPTION_ARG_NONE, NULL, NULL, NULL }
>      };
>      const char *help_msg = N_("Run '" PACKAGE " --help' to see a full list of available command line options");
> @@ -1290,6 +1449,13 @@ int main(int argc, char **argv) {
>      if (error)
>          g_error_free(error);
>  
> +    sync_data();
> +
> +    if (poweroff) {
> +        umount_fs();
> +        reboot(RB_POWER_OFF);
> +        /* Should not be reached, but if it is, kernel will panic anyway */
> +    }
>      return ret;
>  
>   error:
> diff --git a/libvirt-sandbox/libvirt-sandbox-init-qemu.c b/libvirt-sandbox/libvirt-sandbox-init-qemu.c
> index cd6055a..8bde224 100644
> --- a/libvirt-sandbox/libvirt-sandbox-init-qemu.c
> +++ b/libvirt-sandbox/libvirt-sandbox-init-qemu.c
> @@ -424,6 +424,7 @@ main(int argc ATTR_UNUSED, char **argv ATTR_UNUSED)
>  
>      args[narg++] = SANDBOXCONFIGDIR "/.libs/ld.so";
>      args[narg++] = SANDBOXCONFIGDIR "/.libs/libvirt-sandbox-init-common";
> +    args[narg++] = "--poweroff";
>      if (debug)
>          args[narg++] = "-d";
>  

ACK

--
Cedric


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