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Re: [Qemu-devel] [PATCH v6 1/8] virtio_legacy_get_byteswap: endian-ambiv
From: |
Greg Kurz |
Subject: |
Re: [Qemu-devel] [PATCH v6 1/8] virtio_legacy_get_byteswap: endian-ambivalent targets using legacy virtio |
Date: |
Tue, 1 Apr 2014 13:54:16 +0200 |
On Mon, 31 Mar 2014 16:50:55 +0200
Alexander Graf <address@hidden> wrote:
> On 03/28/2014 11:57 AM, Greg Kurz wrote:
> > 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);
> > + }
>
> Couldn't you just reuse virtio_tswap32() here?
>
Yes. Good catch !
> Also, I think a "needs_byteswap" flag gets confusing. Devices shouldn't
> have any access to CPU endian specific RAM accessors.
>
> How about we introduce a flag like "is_bigendian" that we set depending
> on the CPU default endianness for legacy virtio. We can then change that
> flag accordingly. For the wrappers here, we could just use accessors
> like ldl_be_phys() or ldl_le_phys().
>
> That should make things a lot easier to understand - and for virtio 1.0
> we only need to set is_bigendian = false :).
>
Yeah definitely !
>
> Alex
>
>
Thanks.
--
Gregory Kurz address@hidden
address@hidden
Software Engineer @ IBM/Meiosys http://www.ibm.com
Tel +33 (0)562 165 496
"Anarchy is about taking complete responsibility for yourself."
Alan Moore.
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