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virtio_ring: expose virtio barriers for use in vringh.

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The host side of ring needs this logic too.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2013-03-18 13:22:19 +10:30
parent 73640c991e
commit a9a0fef779
2 changed files with 63 additions and 27 deletions
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57
include/linux/virtio_ring.h
View file

@ -4,6 +4,63 @@
#include <linux/irqreturn.h>
#include <uapi/linux/virtio_ring.h>
/*
* Barriers in virtio are tricky. Non-SMP virtio guests can't assume
* they're not on an SMP host system, so they need to assume real
* barriers. Non-SMP virtio hosts could skip the barriers, but does
* anyone care?
*
* For virtio_pci on SMP, we don't need to order with respect to MMIO
* accesses through relaxed memory I/O windows, so smp_mb() et al are
* sufficient.
*
* For using virtio to talk to real devices (eg. other heterogeneous
* CPUs) we do need real barriers. In theory, we could be using both
* kinds of virtio, so it's a runtime decision, and the branch is
* actually quite cheap.
*/
#ifdef CONFIG_SMP
static inline void virtio_mb(bool weak_barriers)
{
if (weak_barriers)
smp_mb();
else
mb();
}
static inline void virtio_rmb(bool weak_barriers)
{
if (weak_barriers)
smp_rmb();
else
rmb();
}
static inline void virtio_wmb(bool weak_barriers)
{
if (weak_barriers)
smp_wmb();
else
wmb();
}
#else
static inline void virtio_mb(bool weak_barriers)
{
mb();
}
static inline void virtio_rmb(bool weak_barriers)
{
rmb();
}
static inline void virtio_wmb(bool weak_barriers)
{
wmb();
}
#endif
struct virtio_device;
struct virtqueue;