virsh: Mention no effect for the --atomic flag in QEMU

[PATCH] virsh: Mention no effect for the --atomic flag in QEMU

Posted by Han Han 5 years ago

According to commit aa65f0f2f1, all logic connected to the
VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC has been removed. Mention that in
virsh manpages.

Signed-off-by: Han Han <hhan@redhat.com>
---
 docs/manpages/virsh.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
index e3afa48f7b..105284a859 100644
--- a/docs/manpages/virsh.rst
+++ b/docs/manpages/virsh.rst
@@ -6859,7 +6859,7 @@ If *--atomic* is specified, libvirt will guarantee that the snapshot
 either succeeds, or fails with no changes; not all hypervisors support
 this.  If this flag is not specified, then some hypervisors may fail
 after partially performing the action, and ``dumpxml`` must be used to
-see whether any partial changes occurred.
+see whether any partial changes occurred. No effect on QEMU hypervisor.
 
 If *--live* is specified, libvirt takes the snapshot while
 the guest is running. Both disk snapshot and domain memory snapshot are
-- 
2.29.2

Re: [PATCH] virsh: Mention no effect for the --atomic flag in QEMU

Posted by Peter Krempa 5 years ago

On Tue, Jan 26, 2021 at 16:31:19 +0800, Han Han wrote:
> According to commit aa65f0f2f1, all logic connected to the
> VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC has been removed. Mention that in
> virsh manpages.
> 
> Signed-off-by: Han Han <hhan@redhat.com>
> ---
>  docs/manpages/virsh.rst | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
> index e3afa48f7b..105284a859 100644
> --- a/docs/manpages/virsh.rst
> +++ b/docs/manpages/virsh.rst
> @@ -6859,7 +6859,7 @@ If *--atomic* is specified, libvirt will guarantee that the snapshot
>  either succeeds, or fails with no changes; not all hypervisors support
>  this.  If this flag is not specified, then some hypervisors may fail
>  after partially performing the action, and ``dumpxml`` must be used to
> -see whether any partial changes occurred.
> +see whether any partial changes occurred. No effect on QEMU hypervisor.

This is actually misleading. The --atomic flag means that the hypervisor
must assure that the snapshot of all disks is taken at a single point in
time.

The qemu hypervisor assures this even without the flag, so that's why
there's no code, but even with the flag used the semantics are
guaranteed.

I don't think this should be reflected in the docs, since the original
meaning of the flag is guaranteed.