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

From: ashish mittal
Subject: Re: [Qemu-devel] [PATCH v8 1/2] block/vxhs.c: Add support for a new block device type called "vxhs"
Date: Mon, 20 Feb 2017 03:34:57 -0800

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.


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