Re: [libvirt PATCH] qemu: Fix domain ID allocation

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On Fri, Jan 31, 2020 at 04:33:50PM +0100, Michal Privoznik wrote:
On 1/31/20 3:43 PM, Ján Tomko wrote:
The rewrite to use GLib's atomic ops functions changed the behavior
of virAtomicIntInc - before it returned the pre-increment value.

Most of the callers using its value were adjusted, but the one
in qemuDriverAllocateID was not. If libvirtd would reconnect to
a running domain during startup, the next started domain would get
the same ID:

$ virsh list
 Id   Name       State
--------------------------
 1    f28live    running
 1    f28live1   running

Use the g_atomic_add function directly (as recommended in viratomic.h)
and add 1 to the result.

This also restores the usual numbering from 1 instead of 0.

Signed-off-by: Ján Tomko <jtomko@xxxxxxxxxx>
Fixes: 7b9645a7d127a374b8d1c83fdf9789706dbab2c9
---
 src/qemu/qemu_conf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index e5051027fc..0b119cbe78 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -1858,7 +1858,7 @@ qemuSetUnprivSGIO(virDomainDeviceDefPtr dev)
 int qemuDriverAllocateID(virQEMUDriverPtr driver)
 {
-    return virAtomicIntInc(&driver->lastvmid);
+    return g_atomic_int_add(&driver->lastvmid, 1) + 1;
 }


Does it makes sense to replace all virAtomic with g_atomic or do we

That does make sense. It is encouraged in viratomic.h, as I said in the
commit message. The reason I did not cleanup all of them is the bugfix
nature of this patch.

still pretend that we care about client library and we don't crash on OOM in it?

I sincerely hope that none of the g_atomic functions allocate memory.

Jano


Michal

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