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Re: [Qemu-devel] [PATCH] Add support for fd: protocol
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH] Add support for fd: protocol |
Date: |
Mon, 23 May 2011 11:19:15 +0100 |
On Mon, May 23, 2011 at 10:45 AM, Daniel P. Berrange
<address@hidden> wrote:
> On Fri, May 20, 2011 at 02:48:23PM -0400, Corey Bryant wrote:
>> sVirt provides SELinux MAC isolation for Qemu guest processes and their
>> corresponding resources (image files). sVirt provides this support
>> by labeling guests and resources with security labels that are stored
>> in file system extended attributes. Some file systems, such as NFS, do
>> not support the extended attribute security namespace, which is needed
>> for image file isolation when using the sVirt SELinux security driver
>> in libvirt.
>>
>> The proposed solution entails a combination of Qemu, libvirt, and
>> SELinux patches that work together to isolate multiple guests' images
>> when they're stored in the same NFS mount. This results in an
>> environment where sVirt isolation and NFS image file isolation can both
>> be provided.
>>
>> Currently, Qemu opens an image file in addition to performing the
>> necessary read and write operations. The proposed solution will move
>> the open out of Qemu and into libvirt. Once libvirt opens an image
>> file for the guest, it will pass the file descriptor to Qemu via a
>> new fd: protocol.
>>
>> If the image file resides in an NFS mount, the following SELinux policy
>> changes will provide image isolation:
>>
>> - A new SELinux boolean is created (e.g. virt_read_write_nfs) to
>> allow Qemu (svirt_t) to only have SELinux read and write
>> permissions on nfs_t files
>>
>> - Qemu (svirt_t) also gets SELinux use permissions on libvirt
>> (virtd_t) file descriptors
>>
>> Following is a sample invocation of Qemu using the fd: protocol:
>>
>> qemu -drive file=fd:4,format=qcow2
>>
>> This patch contains the Qemu code to support this solution. I would
>> like to solicit input from the libvirt community prior to starting
>> the libvirt patch.
>>
>> This patch was tested with the following formats: raw, cow, qcow,
>> qcow2, vmdk, using the fd: protocol as well as existing file name
>> support. Non-valid file descriptors were also tested.
>
> How can backing files work ? The '-drive' syntax doesn't provide
> any way to set properties against the backing files (which may be
> nested to arbitrary depth). AFAICT, we need to the often discussed
> -blockdev advanced syntax to be able to set a 'fd' property against
> nested backing files. I'm not sure it is worth supporting fd: if
> we only have -drive syntax, since backing files are an important
> feature for most mgmt apps.
>
> Also, there are a few places in QEMU, where it re-opens the existing
> block driver on the fly. What is the plan for supporting this, without
> having QEMU block on waiting for libvirt to pass it a new FD ?
QEMU could ask for a file over QMP. So you bootstrap it using fd: but
when a reopen or backing file is needed, QEMU raises a
QEVENT_BLOCK_REQUEST_FILE event. Of course waiting around for the
reopen to complete it not ideal as it may temporarily pause the guest.
Stefan
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, (continued)
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Blue Swirl, 2011/05/20
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Anthony Liguori, 2011/05/20
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Blue Swirl, 2011/05/20
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Kevin Wolf, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Markus Armbruster, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Kevin Wolf, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Blue Swirl, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Anthony Liguori, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Corey Bryant, 2011/05/23
Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Daniel P. Berrange, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Daniel P. Berrange, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Anthony Liguori, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Markus Armbruster, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Jamie Lokier, 2011/05/23
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Stefan Hajnoczi, 2011/05/24
- Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Jamie Lokier, 2011/05/24
Re: [Qemu-devel] [PATCH] Add support for fd: protocol, Anthony Liguori, 2011/05/23