Re: [Qemu-devel] [PATCH v8 1/2] block/vxhs.c: Add support for a new block device type called "vxhs"

[Ketan Nilangekar]

On 2/21/17, 5:59 AM, "Stefan Hajnoczi" <address@hidden> wrote:

    On Mon, Feb 20, 2017 at 03:34:57AM -0800, ashish mittal wrote:
    > On Mon, Feb 20, 2017 at 3:02 AM, Stefan Hajnoczi <address@hidden> wrote:
    > > On Sat, Feb 18, 2017 at 12:30:31AM +0000, Ketan Nilangekar wrote:
    > >> On 2/17/17, 1:42 PM, "Jeff Cody" <address@hidden> wrote:
    > >>
    > >>     On Thu, Feb 16, 2017 at 02:24:19PM -0800, ashish mittal wrote:
    > >>     > Hi,
    > >>     >
    > >>     > I am getting the following error with checkpatch.pl
    > >>     >
    > >>     > ERROR: externs should be avoided in .c files
    > >>     > #78: FILE: block/vxhs.c:28:
    > >>     > +QemuUUID qemu_uuid __attribute__ ((weak));
    > >>     >
    > >>     > Is there any way to get around this, or does it mean that I 
would have
    > >>     > to add a vxhs.h just for this one entry?
    > >>     >
    > >>
    > >>     I remain skeptical on the use of the qemu_uuid as a way to select 
the TLS
    > >>     cert.
    > >>
    > >> [ketan]
    > >> Is there another identity that can be used for uniquely identifying 
instances?
    > >> The requirement was to enforce vdisk access to owner instances.
    > >
    > > The qemu_uuid weak attribute looks suspect.  What is going to provide a
    > > strong qemu_uuid symbol?
    > >
    > > Why aren't configuration parameters like the UUID coming from the QEMU
    > > command-line?
    > >
    > > Stefan
    > 
    > UUID will in fact come from the QEMU command line. VxHS is not doing
    > anything special here. It will just use the value already available to
    > qemu-kvm process.
    > 
    > QemuUUID qemu_uuid;
    > bool qemu_uuid_set;
    > 
    > Both the above are defined in vl.c. vl.c will provide the strong
    > symbol when available. There are certain binaries that do not get
    > linked with vl.c (e.g. qemu-img). The weak symbol will come into
    > affect for such binaries, and in this case, the default VXHS UUID will
    > get picked up. I had, in a previous email, explained how we plan to
    > use the default UUID. In the regular case, the VxHS controller will
    > not allow access to the default UUID (non qemu-kvm) binaries, but it
    > may choose to grant temporary access to specific vdisks for these
    > binaries depending on the workflow.
    
    That idea sounds like a security problem.  During this time window
    anyone could use the default UUID to access the data?
    
    Just make the UUID (or TLS client certificate file) a command-line
    parameter that qemu-system, qemu-img, and other tools accept (e.g.
    qemu-img via the --image-opts/--object syntax).
    
[Ketan]
Sounds fair. Would it be ok to take this up after the driver is merged for the 
upcoming QEMU release?

    Stefan