On 10/14/24 5:17 AM, Daniel P. Berrangé wrote:
On Fri, Oct 11, 2024 at 10:16:51AM -0400, Stefan Berger wrote:
On 10/11/24 10:10 AM, Marc-André Lureau wrote:
Hi
On Fri, Oct 11, 2024 at 5:49 PM Stefan Berger <stefanb@xxxxxxxxxxxxx> wrote:
On 10/4/24 9:32 AM, marcandre.lureau@xxxxxxxxxx wrote:
From: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>
Learn to parse a file path for the TPM state.
Signed-off-by: Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>
---
docs/formatdomain.rst | 19 ++++++++++++++
src/conf/domain_conf.c | 28 +++++++++++++++++++++
src/conf/domain_conf.h | 9 +++++++
src/conf/schemas/domaincommon.rng | 14 +++++++++++
tests/qemuxmlconfdata/tpm-emulator-tpm2.xml | 1 +
5 files changed, 71 insertions(+)
diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 4336cff3ac..992bb98730 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -8173,6 +8173,25 @@ Example: usage of the TPM Emulator
The default version used depends on the combination of hypervisor, guest
architecture, TPM model and backend.
+``source``
+ The ``source`` element specifies the location of the TPM state storage . This
+ element only works with the ``emulator`` backend.
+
+ If not specified, the storage configuration is left to libvirt discretion.
+
+ This element requires that swtpm v0.7 or later is installed.
+
+ The following attributes are supported:
+
+ ``type``
+ The type of storage. It's possible to provide "file" to utilize a single
+ file or block device where the TPM state will be stored.
+
+ ``path``
+ The path to the TPM state storage.
The file backend of swtpm does not do the locking similar to what the
dir backend does because those who added the file backend didn't
need/want it. If we now give full control to the path of the TPM state
file to the user via the domain XML then whose fault is it if two VMs
use the same path to a file backend and stomp on the TPM state file? Is
it the fault of the user because of how he defined the path in the XMLs?
Imho, it's desirable to have a similar locking behaviour regardless of
the backend and prevent users for mistakenly using the same file.
We will only be able to support the locking with an option on the command
line for swtpm (refelected by a new capability verb) and support this series
here once that has become available with a new version of swtpm. Otherwise I
would avoid giving full control to the path to the users but let libvirt
choose a per-VM unique name for the state file.
Relying on libvirt to give a unique path does not avoid the need for
locking, because IME users are liable to do unexpected things like
putting a shared filesystem underneath, and libvirt won't guarantee
any uniqueness across hosts - locking is required for that.
Can we just lock shared block devices without a shared filesystem
somehow supporting the distributed locking? So far swtpm has been using
fcntl(lock_fd, F_SETLK, ...) on a .lock file.
With regards,
Daniel
