[Qemu-devel] [PATCH v6 1/8] virtio_legacy_get_byteswap: endian-ambivalent targets using legacy virtio

[Greg Kurz]

From: Rusty Russell <address@hidden>

virtio data structures are defined as "target endian", which assumes
that's a fixed value.  In fact, that actually means it's platform-specific.
The OASIS virtio 1.0 spec will fix this, by making all little endian.

We need to support both implementations and we want to share as much code
as possible.

A good way to do it is to introduce a per-device boolean property to tell
memory accessors whether they should swap bytes or not. This flag should
be set at device reset time, because:
- endianness won't change while the device is in use, and if we reboot
  into a different endianness, a new device reset will occur
- as suggested by Alexander Graf, we can keep all the logic to set the
  property in a single place and share all the virtio memory accessors
  between the two implementations

For legacy devices, we rely on a per-platform hook to set the flag. The
virtio 1.0 implementation will just have to add some more logic in
virtio_reset() instead of calling the hook:

if (vdev->legacy) {
   vdev->needs_byteswap = virtio_legacy_get_byteswap();
} else {
#ifdef HOST_WORDS_BIGENDIAN
   vdev->needs_byteswap = true;
#else
   vdev->needs_byteswap = false;
#endif
}

The needs_byteswap flag is preserved accross migrations.

Signed-off-by: Rusty Russell <address@hidden>
[ fixed checkpatch.pl error with the virtio_byteswap initialisation,
  ldq_phys() API change,
  relicensed virtio-access.h to GPLv2+ on Rusty's request,
  introduce a per-device needs_byteswap flag,
  add VirtIODevice * arg to virtio helpers,
  rename virtio_get_byteswap to virtio_legacy_get_byteswap,
  Greg Kurz <address@hidden> ]
Signed-off-by: Greg Kurz <address@hidden>
---
 hw/virtio/virtio.c                |    5 +
 include/hw/virtio/virtio-access.h |  139 +++++++++++++++++++++++++++++++++++++
 include/hw/virtio/virtio.h        |    3 +
 stubs/Makefile.objs               |    1 
 stubs/virtio_get_byteswap.c       |    6 ++
 5 files changed, 154 insertions(+)
 create mode 100644 include/hw/virtio/virtio-access.h
 create mode 100644 stubs/virtio_get_byteswap.c

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index aeabf3a..24b565f 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -19,6 +19,7 @@
 #include "hw/virtio/virtio.h"
 #include "qemu/atomic.h"
 #include "hw/virtio/virtio-bus.h"
+#include "hw/virtio/virtio-access.h"
 
 /*
  * The alignment to use between consumer and producer parts of vring.
@@ -546,6 +547,8 @@ void virtio_reset(void *opaque)
 
     virtio_set_status(vdev, 0);
 
+    vdev->needs_byteswap = virtio_legacy_get_byteswap();
+
     if (k->reset) {
         k->reset(vdev);
     }
@@ -845,6 +848,7 @@ void virtio_save(VirtIODevice *vdev, QEMUFile *f)
 
     qemu_put_8s(f, &vdev->status);
     qemu_put_8s(f, &vdev->isr);
+    qemu_put_8s(f, (uint8_t *) &vdev->needs_byteswap);
     qemu_put_be16s(f, &vdev->queue_sel);
     qemu_put_be32s(f, &vdev->guest_features);
     qemu_put_be32(f, vdev->config_len);
@@ -905,6 +909,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f)
 
     qemu_get_8s(f, &vdev->status);
     qemu_get_8s(f, &vdev->isr);
+    qemu_get_8s(f, (uint8_t *) &vdev->needs_byteswap);
     qemu_get_be16s(f, &vdev->queue_sel);
     qemu_get_be32s(f, &features);
 
diff --git a/include/hw/virtio/virtio-access.h 
b/include/hw/virtio/virtio-access.h
new file mode 100644
index 0000000..70dd1e2
--- /dev/null
+++ b/include/hw/virtio/virtio-access.h
@@ -0,0 +1,139 @@
+/*
+ * Virtio Accessor Support: In case your target can change endian.
+ *
+ * Copyright IBM, Corp. 2013
+ *
+ * Authors:
+ *  Rusty Russell   <address@hidden>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ */
+#ifndef _QEMU_VIRTIO_ACCESS_H
+#define _QEMU_VIRTIO_ACCESS_H
+#include "hw/virtio/virtio.h"
+
+static inline uint16_t virtio_lduw_phys(AddressSpace *as, hwaddr pa,
+                                        struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        return bswap16(lduw_phys(as, pa));
+    }
+    return lduw_phys(as, pa);
+}
+
+static inline uint32_t virtio_ldl_phys(AddressSpace *as, hwaddr pa,
+                                       struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        return bswap32(ldl_phys(as, pa));
+    }
+    return ldl_phys(as, pa);
+}
+
+static inline uint64_t virtio_ldq_phys(AddressSpace *as, hwaddr pa,
+                                       struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        return bswap64(ldq_phys(as, pa));
+    }
+    return ldq_phys(as, pa);
+}
+
+static inline void virtio_stw_phys(AddressSpace *as, hwaddr pa, uint16_t value,
+                                   struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        stw_phys(as, pa, bswap16(value));
+    } else {
+        stw_phys(as, pa, value);
+    }
+}
+
+static inline void virtio_stl_phys(AddressSpace *as, hwaddr pa, uint32_t value,
+                                   struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        stl_phys(as, pa, bswap32(value));
+    } else {
+        stl_phys(as, pa, value);
+    }
+}
+
+static inline void virtio_stw_p(void *ptr, uint16_t v,
+                                struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        stw_p(ptr, bswap16(v));
+    } else {
+        stw_p(ptr, v);
+    }
+}
+
+static inline void virtio_stl_p(void *ptr, uint32_t v,
+                                struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        stl_p(ptr, bswap32(v));
+    } else {
+        stl_p(ptr, v);
+    }
+}
+
+static inline void virtio_stq_p(void *ptr, uint64_t v,
+                                struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        stq_p(ptr, bswap64(v));
+    } else {
+        stq_p(ptr, v);
+    }
+}
+
+static inline int virtio_lduw_p(const void *ptr, struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        return bswap16(lduw_p(ptr));
+    } else {
+        return lduw_p(ptr);
+    }
+}
+
+static inline int virtio_ldl_p(const void *ptr, struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        return bswap32(ldl_p(ptr));
+    } else {
+        return ldl_p(ptr);
+    }
+}
+
+static inline uint64_t virtio_ldq_p(const void *ptr, struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        return bswap64(ldq_p(ptr));
+    } else {
+        return ldq_p(ptr);
+    }
+}
+
+static inline uint32_t virtio_tswap32(uint32_t s, struct VirtIODevice *vdev)
+{
+    if (vdev->needs_byteswap) {
+        return bswap32(tswap32(s));
+    } else {
+        return tswap32(s);
+    }
+}
+
+static inline void virtio_tswap32s(uint32_t *s, struct VirtIODevice *vdev)
+{
+    tswap32s(s);
+    if (vdev->needs_byteswap) {
+        *s = bswap32(*s);
+    }
+}
+#endif /* _QEMU_VIRTIO_ACCESS_H */
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 3e54e90..3595da5 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -121,6 +121,7 @@ struct VirtIODevice
     bool vm_running;
     VMChangeStateEntry *vmstate;
     char *bus_name;
+    bool needs_byteswap;
 };
 
 typedef struct VirtioDeviceClass {
@@ -253,4 +254,6 @@ void virtio_queue_set_host_notifier_fd_handler(VirtQueue 
*vq, bool assign,
                                                bool set_handler);
 void virtio_queue_notify_vq(VirtQueue *vq);
 void virtio_irq(VirtQueue *vq);
+
+extern bool virtio_legacy_get_byteswap(void);
 #endif
diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
index 5ed1d38..a13381a 100644
--- a/stubs/Makefile.objs
+++ b/stubs/Makefile.objs
@@ -30,3 +30,4 @@ stub-obj-y += vmstate.o
 stub-obj-$(CONFIG_WIN32) += fd-register.o
 stub-obj-y += cpus.o
 stub-obj-y += kvm.o
+stub-obj-y += virtio_get_byteswap.o
diff --git a/stubs/virtio_get_byteswap.c b/stubs/virtio_get_byteswap.c
new file mode 100644
index 0000000..28af5e3
--- /dev/null
+++ b/stubs/virtio_get_byteswap.c
@@ -0,0 +1,6 @@
+#include "hw/virtio/virtio.h"
+
+bool virtio_legacy_get_byteswap(void)
+{
+    return false;
+}