[libvirt] [PATCH] Make saving domain XML more robust

[Daniel P. Berrange]

On Thu, Oct 06, 2011 at 12:22:01PM +0200, Jiri Denemark wrote:
> When saving domain XML (either config or status) we just overwrite old
> content of the file. In case something fails during that process (e.g.
> disk gets full) we lose both old and new content. This patch makes the
> process more robust by writing the new content into a separate file and
> only if that succeeds the original file is atomically replaced with the
> new one.
> ---
>  src/conf/domain_conf.c |   25 +++++++++++++++++++++----
>  1 files changed, 21 insertions(+), 4 deletions(-)

By doing this you've almost addressed this BZ...

   https://bugzilla.redhat.com/show_bug.cgi?id=489946

...almost...

Checkout slides 78 -> 119 of the presentation linked there,
paying note to the horrible tales of woe about OS-X and fsync() :-(
We probably want to add some kind of virFileSync(int fd)  API call
that does the neccessary black magic.

>  
>      if (VIR_CLOSE(fd) < 0) {
>          virReportSystemError(errno,
>                               _("cannot save config file '%s'"),
> -                             configFile);
> +                             newfile);
> +        goto cleanup;
> +    }
> +
> +    if (rename(newfile, configFile) < 0) {
> +        virReportSystemError(errno,
> +                             _("cannot rename config file '%s' as '%s'"),
> +                             newfile, configFile);
>          goto cleanup;
>      }

Regards,
Daniel
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