On Tue, Jan 12, 2016 at 11:31:00AM +0100, Greg Kurz wrote:

On Tue, 12 Jan 2016 12:01:32 +0200
"Michael S. Tsirkin" [off-list ref] wrote:

quoted

On Mon, Jan 11, 2016 at 03:39:38PM +0100, Greg Kurz wrote:

quoted

The vq->is_le field is used to fix endianness when accessing the vring via
the cpu_to_vhost16() and vhost16_to_cpu() helpers in the following cases:

1) host is big endian and device is modern virtio

2) host has cross-endian support and device is legacy virtio with a different
   endianness than the host

Both cases rely on the VHOST_SET_FEATURES ioctl, but 2) also needs the
VHOST_SET_VRING_ENDIAN ioctl to be called by userspace. Since vq->is_le
is only needed when the backend is active, it was decided to set it at
backend start.

This is currently done in vhost_init_used()->vhost_init_is_le() but it
obfuscates the core vhost code. This patch moves the is_le setup to a
dedicated function that is called from the backend code.

Note vhost_net is the only backend that can pass vq->private_data == NULL to
vhost_init_used(), hence the "if (sock)" branch.

No behaviour change.

Reviewed-by: Cornelia Huck <redacted>
Signed-off-by: Greg Kurz <redacted>
---

Hi Michael,

This is a cleanup patch I had posted last year:

http://patchwork.ozlabs.org/patch/538277/

I am just reposting with Cornelia's R-b.

Cheers.

--
Greg

 drivers/vhost/net.c   |    6 ++++++
 drivers/vhost/scsi.c  |    3 +++
 drivers/vhost/test.c  |    2 ++
 drivers/vhost/vhost.c |   12 +++++++-----
 drivers/vhost/vhost.h |    1 +
 5 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 9eda69e40678..d6319cb2664c 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c

@@ -917,6 +917,12 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 
 		vhost_net_disable_vq(n, vq);
 		vq->private_data = sock;
+
+		if (sock)
+			vhost_set_is_le(vq);
+		else
+			vq->is_le = virtio_legacy_is_little_endian();
+
 		r = vhost_init_used(vq);
 		if (r)
 			goto err_used;  

This part is kind of ugly. I think it's cleaner is the generic code.
How about we teach vhost_set_is_le to test vq->private_data and DTRT?

You're right. I'll try that.

quoted

quoted

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 29cfc57d496e..1f4f405ebba8 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c

@@ -1274,6 +1274,9 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
 			vq = &vs->vqs[i].vq;
 			mutex_lock(&vq->mutex);
 			vq->private_data = vs_tpg;
+
+			vhost_set_is_le(vq);
+
 			vhost_init_used(vq);
 			mutex_unlock(&vq->mutex);
 		}

diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index f2882ac98726..b1c7df502211 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c

@@ -196,6 +196,8 @@ static long vhost_test_run(struct vhost_test *n, int test)
 		oldpriv = vq->private_data;
 		vq->private_data = priv;
 
+		vhost_set_is_le(vq);
+
 		r = vhost_init_used(&n->vqs[index]);
 
 		mutex_unlock(&vq->mutex);

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index ad2146a9ab2d..e688eb801d43 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c

@@ -113,6 +113,12 @@ static void vhost_init_is_le(struct vhost_virtqueue *vq)
 }
 #endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */
 
+void vhost_set_is_le(struct vhost_virtqueue *vq)
+{
+	vhost_init_is_le(vq);
+}
+EXPORT_SYMBOL_GPL(vhost_set_is_le);
+
 static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
 			    poll_table *pt)
 {  

Why do we need this wrapper? Why not just export vhost_init_is_le?

This is a tentative workaround to:

WARNING: EXPORT_SYMBOL(foo); should immediately follow its function/variable
#35: FILE: drivers/vhost/vhost.c:116:
+EXPORT_SYMBOL_GPL(vhost_init_is_le);

Other possibility is to put the EXPORT_SYMBOL_GPL statement in both
conditional compilation blocks. Maybe better ?

That, or ignore the warning.

quoted

Or rename vhost_init_is_le->vhost_set_is_le if you prefer.

quoted

@@ -1156,12 +1162,8 @@ int vhost_init_used(struct vhost_virtqueue *vq)
 {
 	__virtio16 last_used_idx;
 	int r;
-	if (!vq->private_data) {
-		vq->is_le = virtio_legacy_is_little_endian();
+	if (!vq->private_data)
 		return 0;
-	}
-
-	vhost_init_is_le(vq);
 
 	r = vhost_update_used_flags(vq);
 	if (r)

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index d3f767448a72..af5d33797937 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h

@@ -162,6 +162,7 @@ bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
 
 int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
 		    unsigned int log_num, u64 len);
+void vhost_set_is_le(struct vhost_virtqueue *vq);
 
 #define vq_err(vq, fmt, ...) do {                                  \
 		pr_debug(pr_fmt(fmt), ##__VA_ARGS__);       \