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.

Signed-off-by: Greg Kurz <gk...@linux.vnet.ibm.com>
---
 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;
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index e25a23692822..e2644a301fa5 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1276,6 +1276,9 @@ 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 eec2f11809ff..6be863dcbd13 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)
 {
@@ -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 4772862b71a7..8a62041959fe 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__);       \

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