Re: [PATCH] virStorageVolWipe: Document that wiping journaled FS is useless

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On 12/17/2015 05:10 AM, Michal Privoznik wrote:
> So you have a libvirt volume that you want to wipe out. But lets
> say that the volume is actually a file stored on a journaled
> filesystem. Overwriting it with zeroes or a pattern does not mean
> that corresponding physical location on the disk is overwritten
> too, due to journaling. It's the same story with network based
> volumes, copy-on-write filesystems, and so on. Since there is no
> way that an userland application can write onto specific areas on
> disk, all that we can do is document the fact.
> 
> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
> ---
>  src/libvirt-storage.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 

Seems reasonable.  Is there an associated bz?

ACK -

John
> diff --git a/src/libvirt-storage.c b/src/libvirt-storage.c
> index 66dd9f0..513c72f 100644
> --- a/src/libvirt-storage.c
> +++ b/src/libvirt-storage.c
> @@ -1725,7 +1725,12 @@ virStorageVolDelete(virStorageVolPtr vol,
>   * @vol: pointer to storage volume
>   * @flags: extra flags; not used yet, so callers should always pass 0
>   *
> - * Ensure data previously on a volume is not accessible to future reads
> + * Ensure data previously on a volume is not accessible to future
> + * reads. Also note, that depending on the actual volume
> + * representation, this call may not really overwrite the
> + * physical location of the volume. For instance, files stored
> + * journaled, log structured, copy-on-write, versioned, and
> + * network file systems are known to be problematic.
>   *
>   * Returns 0 on success, or -1 on error
>   */
> @@ -1765,8 +1770,13 @@ virStorageVolWipe(virStorageVolPtr vol,
>   * @algorithm: one of virStorageVolWipeAlgorithm
>   * @flags: future flags, use 0 for now
>   *
> - * Similar to virStorageVolWipe, but one can choose
> - * between different wiping algorithms.
> + * Similar to virStorageVolWipe, but one can choose between
> + * different wiping algorithms. Also note, that depending on the
> + * actual volume representation, this call may not really
> + * overwrite the physical location of the volume. For instance,
> + * files stored journaled, log structured, copy-on-write,
> + * versioned, and network file systems are known to be
> + * problematic.
>   *
>   * Returns 0 on success, or -1 on error.
>   */
> 

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