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

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(a)redhat.com&gt; --- src/libvirt-storage.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) 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. */ -- 2.4.10