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| author | Michael S. Tsirkin <mst@redhat.com> | 2009-10-26 15:17:15 +0200 |
|---|---|---|
| committer | Anthony Liguori <aliguori@us.ibm.com> | 2009-10-30 08:39:34 -0500 |
| commit | 79758e95d7f018dabd726bf7eb8cdd087692410c (patch) | |
| tree | 2cf8a7cf6696a35bb3e0f8ad3d9bf8df48894c0b /hw | |
| parent | 1e5b9d2fccb205ed8fc84fb38945b8fb3d225640 (diff) | |
| download | qemu-79758e95d7f018dabd726bf7eb8cdd087692410c.zip qemu-79758e95d7f018dabd726bf7eb8cdd087692410c.tar.gz qemu-79758e95d7f018dabd726bf7eb8cdd087692410c.tar.bz2 | |
qemu/virtio: make wmb compiler barrier + comments
wmb must be at least a compiler barrier, even without SMP.
Further, we likely need some rmb()/mb() as well:
I have not audited the code but lguest has mb(),
add a comment for now.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Diffstat (limited to 'hw')
| -rw-r--r-- | hw/virtio.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/hw/virtio.c b/hw/virtio.c index 337ff27..1f92171 100644 --- a/hw/virtio.c +++ b/hw/virtio.c @@ -23,8 +23,11 @@ /* QEMU doesn't strictly need write barriers since everything runs in * lock-step. We'll leave the calls to wmb() in though to make it obvious for * KVM or if kqemu gets SMP support. + * In any case, we must prevent the compiler from reordering the code. + * TODO: we likely need some rmb()/mb() as well. */ -#define wmb() do { } while (0) + +#define wmb() __asm__ __volatile__("": : :"memory") typedef struct VRingDesc { |