Patchwork migration: flush migration data to disk.

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Submitter Gerd Hoffmann
Date Oct. 26, 2011, 10:39 a.m.
Message ID <1319625554-6020-1-git-send-email-kraxel@redhat.com>
Download mbox | patch
Permalink /patch/121878/
State New
Headers show

Comments

Gerd Hoffmann - Oct. 26, 2011, 10:39 a.m.
This patch increases robustness when migrating to a file with
two little changes:

 (1) Before closing the migration file handle checks if it happens to be
     a regular file and if so it issues a fsync.  This way the data is
     flushed to disk before qemu sends the migration completed event.
 (2) It adds error checking.  In case either fsync or close syscall
     fails pass up the error (and fail migration).

Cc: Jiri Denemark <jdenemar@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 migration-fd.c |   21 ++++++++++++++++++++-
 1 files changed, 20 insertions(+), 1 deletions(-)
Juan Quintela - Oct. 26, 2011, 1:07 p.m.
Gerd Hoffmann <kraxel@redhat.com> wrote:
> This patch increases robustness when migrating to a file with
> two little changes:
>
>  (1) Before closing the migration file handle checks if it happens to be
>      a regular file and if so it issues a fsync.  This way the data is
>      flushed to disk before qemu sends the migration completed event.
>  (2) It adds error checking.  In case either fsync or close syscall
>      fails pass up the error (and fail migration).
>
> Cc: Jiri Denemark <jdenemar@redhat.com>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  migration-fd.c |   21 ++++++++++++++++++++-
>  1 files changed, 20 insertions(+), 1 deletions(-)
>
> diff --git a/migration-fd.c b/migration-fd.c
> index d0aec89..2206494 100644
> --- a/migration-fd.c
> +++ b/migration-fd.c
> @@ -42,10 +42,29 @@ static int fd_write(MigrationState *s, const void * buf, size_t size)
>  
>  static int fd_close(MigrationState *s)
>  {
> +    struct stat st;
> +    int ret;
> +
>      DPRINTF("fd_close\n");
>      if (s->fd != -1) {
> -        close(s->fd);
> +        ret = fstat(s->fd, &st);
> +        if (ret == 0 && S_ISREG(st.st_mode)) {
> +            /*
> +             * If the file handle is a regular file make sure the
> +             * data is flushed to disk before signaling success.
> +             */
> +            ret = fsync(s->fd);
> +            if (ret != 0) {
> +                perror("migration-fd: fsync");
> +                return -1;

return -error, please.
Trying to get all callers to check the error returns.  (and yes, none of
the close calls check for errors on close)


> +            }
> +        }
> +        ret = close(s->fd);
>          s->fd = -1;
> +        if (ret != 0) {
> +            perror("migration-fd: close");
> +            return -1;
> +        }
>      }
>      return 0;
>  }

Patch

diff --git a/migration-fd.c b/migration-fd.c
index d0aec89..2206494 100644
--- a/migration-fd.c
+++ b/migration-fd.c
@@ -42,10 +42,29 @@  static int fd_write(MigrationState *s, const void * buf, size_t size)
 
 static int fd_close(MigrationState *s)
 {
+    struct stat st;
+    int ret;
+
     DPRINTF("fd_close\n");
     if (s->fd != -1) {
-        close(s->fd);
+        ret = fstat(s->fd, &st);
+        if (ret == 0 && S_ISREG(st.st_mode)) {
+            /*
+             * If the file handle is a regular file make sure the
+             * data is flushed to disk before signaling success.
+             */
+            ret = fsync(s->fd);
+            if (ret != 0) {
+                perror("migration-fd: fsync");
+                return -1;
+            }
+        }
+        ret = close(s->fd);
         s->fd = -1;
+        if (ret != 0) {
+            perror("migration-fd: close");
+            return -1;
+        }
     }
     return 0;
 }