[RFC PATCH 1/4] vhost: add VHOST_VRING_F_BYTESWAP flag

Cédric Le Goater
2014-10-29T08:40:03Z

The VHOST_VRING_F_BYTESWAP flag will be used by the host to byteswap
the vring data when the guest and the host have a different endian
order.

Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
---
drivers/vhost/vhost.c | 5 ++++-
drivers/vhost/vhost.h | 1 +
include/uapi/linux/vhost.h | 3 +++
3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c90f4374442a..72c21b790ba3 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -199,6 +199,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->call = NULL;
vq->log_ctx = NULL;
vq->memory = NULL;
+ vq->byteswap = 0;
}

static int vhost_worker(void *data)
@@ -701,7 +702,8 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
r = -EFAULT;
break;
}
- if (a.flags & ~(0x1 << VHOST_VRING_F_LOG)) {
+ if (a.flags & ~(0x1 << VHOST_VRING_F_LOG |
+ 0x1 << VHOST_VRING_F_BYTESWAP)) {
r = -EOPNOTSUPP;
break;
}
@@ -747,6 +749,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
vq->avail = (void __user *)(unsigned long)a.avail_user_addr;
vq->log_addr = a.log_guest_addr;
vq->used = (void __user *)(unsigned long)a.used_user_addr;
+ vq->byteswap = !!(a.flags & (0x1 << VHOST_VRING_F_BYTESWAP));
break;
case VHOST_SET_VRING_KICK:
if (copy_from_user(&f, argp, sizeof f)) {
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 3eda654b8f5a..ab25b7d0720d 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -110,6 +110,7 @@ struct vhost_virtqueue {
/* Log write descriptors */
void __user *log_base;
struct vhost_log *log;
+ bool byteswap;
};

struct vhost_dev {
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index bb6a5b4cb3c5..6a8c2b325c44 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -34,6 +34,9 @@ struct vhost_vring_addr {
/* Flag values: */
/* Whether log address is valid. If set enables logging. */
#define VHOST_VRING_F_LOG 0
+ /* Whether vring memory accesses should be byte-swapped.
+ * required when the guest has a different endianness */
+#define VHOST_VRING_F_BYTESWAP 1

/* Start of array of descriptors (virtually contiguous) */
__u64 desc_user_addr;
--
1.7.10.4