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Re: [libvirt] [PATCH 2/4] Avoid create/unlink with block devs used for QEMU save



On Wed, Apr 21, 2010 at 05:56:11PM +0100, Daniel P. Berrange wrote:
> It is possible to use block devices with domain save/restore. Upon
> failure QEMU unlinks the path being saved to. This isn't good when
> it is a block device !
> 
> * src/qemu/qemu_driver.c: Don't unlink block devices if save fails
> ---
>  src/qemu/qemu_driver.c |   22 ++++++++++++++++++++--
>  1 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 91fe963..50cd982 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -4787,6 +4787,8 @@ static int qemudDomainSaveFlag(virDomainPtr dom, const char *path,
>      int rc;
>      virDomainEventPtr event = NULL;
>      qemuDomainObjPrivatePtr priv;
> +    struct stat sb;
> +    int is_bdev = 0;
>  
>      memset(&header, 0, sizeof(header));
>      memcpy(header.magic, QEMUD_SAVE_MAGIC, sizeof(header.magic));
> @@ -4840,6 +4842,21 @@ static int qemudDomainSaveFlag(virDomainPtr dom, const char *path,
>      }
>      header.xml_len = strlen(xml) + 1;
>  
> +    /* path might be a pre-existing block dev, in which case
> +     * we need to skip the create step, and also avoid unlink
> +     * in the failure case */
> +    if (stat(path, &sb) < 0) {
> +        if (errno != ENOENT) {
> +            virReportSystemError(errno, _("unable to access %s"), path);
> +            goto endjob;
> +        } else {
> +            is_bdev = 0;
> +        }

  what about EACCESS can we fail stat() but still be able to append to
the file ? That sounds unlikely though...

> +    } else {
> +        is_bdev = S_ISBLK(sb.st_mode);
> +    }
> +
> +
>      /* Setup hook data needed by virFileOperation hook function */
>      hdata.dom = dom;
>      hdata.path = path;
> @@ -4849,7 +4866,8 @@ static int qemudDomainSaveFlag(virDomainPtr dom, const char *path,
>      /* Write header to file, followed by XML */
>  
>      /* First try creating the file as root */
> -    if ((rc = virFileOperation(path, O_CREAT|O_TRUNC|O_WRONLY,
> +    if (!is_bdev &&
> +        (rc = virFileOperation(path, O_CREAT|O_TRUNC|O_WRONLY,
>                                 S_IRUSR|S_IWUSR,
>                                 getuid(), getgid(),
>                                 qemudDomainSaveFileOpHook, &hdata,
> @@ -5014,7 +5032,7 @@ endjob:
>  
>  cleanup:
>      VIR_FREE(xml);
> -    if (ret != 0)
> +    if (ret != 0 && !is_bdev)
>          unlink(path);
>      if (vm)
>          virDomainObjUnlock(vm);

ACK,

Daniel

-- 
Daniel Veillard      | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
daniel veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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