Re: [Qemu-devel] [PATCH 11/34] qmp: query-block: add 'valid_encryption_key' field

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 10 Aug 2012 09:56:11 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Revisited this one on review of v2, replying here for context.
> 
> Luiz Capitulino <lcapitulino@redhat.com> writes:
> 
> > On Thu, 02 Aug 2012 13:35:54 +0200
> > Markus Armbruster <armbru@redhat.com> wrote:
> >
> >> Luiz Capitulino <lcapitulino@redhat.com> writes:
> >> 
> >> > Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> >> > ---
> >> >  block.c          | 1 +
> >> >  qapi-schema.json | 7 +++++--
> >> >  2 files changed, 6 insertions(+), 2 deletions(-)
> >> >
> >> > diff --git a/block.c b/block.c
> >> > index b38940b..9c113b8 100644
> >> > --- a/block.c
> >> > +++ b/block.c
> >> > @@ -2445,6 +2445,7 @@ BlockInfoList *qmp_query_block(Error **errp)
> >> >              info->value->inserted->ro = bs->read_only;
> >> >              info->value->inserted->drv = g_strdup(bs->drv->format_name);
> >> >              info->value->inserted->encrypted = bs->encrypted;
> >> > +            info->value->inserted->valid_encryption_key = bs->valid_key;
> >> >              if (bs->backing_file[0]) {
> >> >                  info->value->inserted->has_backing_file = true;
> >> >                  info->value->inserted->backing_file = g_strdup(bs->backing_file);
> >> > diff --git a/qapi-schema.json b/qapi-schema.json
> >> > index bc55ed2..1b2d7f5 100644
> >> > --- a/qapi-schema.json
> >> > +++ b/qapi-schema.json
> >> > @@ -400,6 +400,8 @@
> >> >  #
> >> >  # @encrypted: true if the backing device is encrypted
> >> >  #
> >> > +# @valid_encryption_key: true if a valid encryption key has been set
> >> > +#
> >> >  # @bps: total throughput limit in bytes per second is specified
> >> >  #
> >> >  # @bps_rd: read throughput limit in bytes per second is specified
> >> > @@ -419,8 +421,9 @@
> >> >  { 'type': 'BlockDeviceInfo',
> >> >    'data': { 'file': 'str', 'ro': 'bool', 'drv': 'str',
> >> >              '*backing_file': 'str', 'encrypted': 'bool',
> >> > -            'bps': 'int', 'bps_rd': 'int', 'bps_wr': 'int',
> >> > -            'iops': 'int', 'iops_rd': 'int', 'iops_wr': 'int'} }
> >> > +            'valid_encryption_key': 'bool', 'bps': 'int',
> >> > +            'bps_rd': 'int', 'bps_wr': 'int', 'iops': 'int',
> >> > +            'iops_rd': 'int', 'iops_wr': 'int'} }
> >> >  
> >> >  ##
> >> >  # @BlockDeviceIoStatus:
> >> 
> >> BlockDeviceInfo is API, isn't it?
> >
> > Yes.
> >
> >> Note that bs->valid_key currently implies bs->encrypted.  bs->valid_key
> >> && !bs->encrypted is impossible.  Should we make valid_encryption_key
> >> only available when encrypted?
> >
> > I don't think so. It's a bool, so it's ok for it to be false when
> > encrypted is false.
> 
> What bothers me is encrypted=false, valid_encryption_key=true.

Disappearing keys is worse, IMHO (assuming that that situation is impossible
in practice, of course).

> >> valid_encryption_key is a bit long for my taste.  Yours may be
> >> different.
> >
> > We should choose more descriptive and self-documenting names for the
> > protocol. Besides, I can't think of anything shorter that won't get
> > cryptic.
> >
> > Suggestions are always welcome though :)
> 
> valid_encryption_key sounds like the value is the valid key.

That's exactly what it is.

> got_crypt_key?  Also avoids "valid".  Good, because current encrypted
> formats don't actually validate the key; they happily accept any key.

That's a block layer bug, not QMP's.

QMP clients are going to be misguided by valid_encryption_key the same way
they are with the block_passwd command or how we suffer from it internally
when calling bdrv_set_key() (which also manifests itself in HMP).

Fixing the bug where it is will automatically fix all its instances.

> GIGO.  In theory, you can trash a disk that way.  In practice, we can
> hope the guest will refuse to touch the disk, because it can't recognize
> partition table / filesystems.