Re: [PATCH v4 7/8] vhost: feature to set the vring endianness
On Wed, Apr 22, 2015 at 11:08:54AM +0200, Greg Kurz wrote:
On Tue, 21 Apr 2015 20:25:03 +0200
Michael S. Tsirkin m...@redhat.com wrote:
[ ... ]
@@ -630,6 +634,53 @@ static long vhost_set_memory(struct vhost_dev
*d, struct vhost_memory __user *m)
return 0;
}
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+int __user *argp)
+{
+ struct vhost_vring_state s;
+
+ if (vq-private_data)
+ return -EBUSY;
+
+ if (copy_from_user(s, argp, sizeof(s)))
+ return -EFAULT;
+
+ if (s.num s.num != 1)
s.num ~0x1
Since s.num is unsigned and I assume this won't change, what about
s.num 1 as suggested by Cornelia ?
I just tried and gcc optimizes
s.num != 0 s.num != 1 to s.num 1
The former will be more readable once we
replace 0 and 1 with defines.
So ignore my advice, keep code as is but use defines.
Ok.
[ ... ]
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -103,6 +103,15 @@ struct vhost_memory {
/* Get accessor: reads index, writes value in num */
#define VHOST_GET_VRING_BASE _IOWR(VHOST_VIRTIO, 0x12, struct
vhost_vring_state)
+/* Set the vring byte order in num. This is a legacy only API that
is simply
+ * ignored when VIRTIO_F_VERSION_1 is set.
+ * 0 to set to little-endian
+ * 1 to set to big-endian
How about defines for these?
Ok. I'll put the defines here so that all the cross-endian stuff
lies in the same hunk. Is it ok for you ?
Fine.
+ * other values return EINVAL.
Pls also add a note saying that not all kernel configurations support this
ioctl,
but all configurations that support SET also support GET.
Ok.
+ */
+#define VHOST_SET_VRING_BIG_ENDIAN _IOW(VHOST_VIRTIO, 0x13, struct
vhost_vring_state)
+#define VHOST_GET_VRING_BIG_ENDIAN _IOW(VHOST_VIRTIO, 0x14, struct
vhost_vring_state)
+
/* The following ioctls use eventfd file descriptors to signal and
poll
* for events. */
I'm inclined to think VHOST_SET_VRING_ENDIAN is a slightly better name.
What do you think?
Or VHOST_SET_VRING_CROSS_ENDIAN ? I like the idea to keep a hint that this
API is for cross-endian only... like the rest of this series.
--
Greg
I think VHOST_SET_VRING_CROSS_ENDIAN is not a good name -
it would imply 1 for cross endian, 0 for native endian.
--
MST
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Re: [PATCH v4 7/8] vhost: feature to set the vring endianness
On Tue, 21 Apr 2015 20:25:03 +0200
Michael S. Tsirkin m...@redhat.com wrote:
[ ... ]
@@ -630,6 +634,53 @@ static long vhost_set_memory(struct vhost_dev *d,
struct vhost_memory __user *m)
return 0;
}
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+ int __user *argp)
+{
+ struct vhost_vring_state s;
+
+ if (vq-private_data)
+ return -EBUSY;
+
+ if (copy_from_user(s, argp, sizeof(s)))
+ return -EFAULT;
+
+ if (s.num s.num != 1)
s.num ~0x1
Since s.num is unsigned and I assume this won't change, what about
s.num 1 as suggested by Cornelia ?
I just tried and gcc optimizes
s.num != 0 s.num != 1 to s.num 1
The former will be more readable once we
replace 0 and 1 with defines.
So ignore my advice, keep code as is but use defines.
Ok.
[ ... ]
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -103,6 +103,15 @@ struct vhost_memory {
/* Get accessor: reads index, writes value in num */
#define VHOST_GET_VRING_BASE _IOWR(VHOST_VIRTIO, 0x12, struct
vhost_vring_state)
+/* Set the vring byte order in num. This is a legacy only API that is
simply
+ * ignored when VIRTIO_F_VERSION_1 is set.
+ * 0 to set to little-endian
+ * 1 to set to big-endian
How about defines for these?
Ok. I'll put the defines here so that all the cross-endian stuff
lies in the same hunk. Is it ok for you ?
Fine.
+ * other values return EINVAL.
Pls also add a note saying that not all kernel configurations support this
ioctl,
but all configurations that support SET also support GET.
Ok.
+ */
+#define VHOST_SET_VRING_BIG_ENDIAN _IOW(VHOST_VIRTIO, 0x13, struct
vhost_vring_state)
+#define VHOST_GET_VRING_BIG_ENDIAN _IOW(VHOST_VIRTIO, 0x14, struct
vhost_vring_state)
+
/* The following ioctls use eventfd file descriptors to signal and poll
* for events. */
I'm inclined to think VHOST_SET_VRING_ENDIAN is a slightly better name.
What do you think?
Or VHOST_SET_VRING_CROSS_ENDIAN ? I like the idea to keep a hint that this
API is for cross-endian only... like the rest of this series.
--
Greg
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Re: [PATCH v4 7/8] vhost: feature to set the vring endianness
On Tue, Apr 21, 2015 at 05:48:20PM +0200, Greg Kurz wrote:
On Tue, 21 Apr 2015 16:04:23 +0200
Michael S. Tsirkin m...@redhat.com wrote:
On Fri, Apr 10, 2015 at 12:19:16PM +0200, Greg Kurz wrote:
This patch brings cross-endian support to vhost when used to implement
legacy virtio devices. Since it is a relatively rare situation, the
feature availability is controlled by a kernel config option (not set
by default).
The vq-is_le boolean field is added to cache the endianness to be
used for ring accesses. It defaults to native endian, as expected
by legacy virtio devices. When the ring gets active, we force little
endian if the device is modern. When the ring is deactivated, we
revert to the native endian default.
If cross-endian was compiled in, a vq-user_be boolean field is added
so that userspace may request a specific endianness. This field is
used to override the default when activating the ring of a legacy
device. It has no effect on modern devices.
Signed-off-by: Greg Kurz gk...@linux.vnet.ibm.com
---
drivers/vhost/Kconfig | 10 ++the
drivers/vhost/vhost.c | 76
+++-
drivers/vhost/vhost.h | 12 +--
include/uapi/linux/vhost.h |9 +
4 files changed, 103 insertions(+), 4 deletions(-)
Changes since v3:
- VHOST_SET_VRING_ENDIAN_LEGACY ioctl renamed to
VHOST_SET_VRING_BIG_ENDIAN
- ioctl API is now: 0 for le, 1 for be, other values are EINVAL
- ioctl doesn't filter out modern devices
- ioctl stubs return ENOIOCTLCMD
- forbid endianness changes when vring is active
- logic now handled with vq-is_le and vq-user_be according to device
start/stop as suggested by Michael
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 017a1e8..0aec88c 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -32,3 +32,13 @@ config VHOST
---help---
This option is selected by any driver which needs to access
the core of vhost.
+
+config VHOST_SET_ENDIAN_LEGACY
I'd prefer namin this VHOST_CROSS_ENDIAN_LEGACY
Yes, makes sense. I'll make sure most of the cross-endian changes are
easy to grep.
+ bool Cross-endian support for host kernel accelerator
+ default n
+ ---help---
+ This option allows vhost to support guests with a different byte
+ ordering from host. It is disabled by default since it adds overhead
+ and it is only needed by a few platforms (powerpc and arm).
and is only useful on a few platforms (powerpc and arm).
it seems to refer to overhead, which is rarely needed.
needed is a bit too strong, you can always e.g. run virtio
in userspace.
My poor English again... it seems you understood what I wanted to
write though :)
+
+ If unsure, say N.
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2ee2826..3eb756b 100644the
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -199,6 +199,10 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq-call = NULL;
vq-log_ctx = NULL;
vq-memory = NULL;
+ vq-is_le = virtio_legacy_is_little_endian();
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+ vq-user_be = !vq-is_le;
+#endif
add a wrapper for this too?
Will do.
}
static int vhost_worker(void *data)
@@ -630,6 +634,53 @@ static long vhost_set_memory(struct vhost_dev *d,
struct vhost_memory __user *m)
return 0;
}
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+int __user *argp)
+{
+ struct vhost_vring_state s;
+
+ if (vq-private_data)
+ return -EBUSY;
+
+ if (copy_from_user(s, argp, sizeof(s)))
+ return -EFAULT;
+
+ if (s.num s.num != 1)
s.num ~0x1
Since s.num is unsigned and I assume this won't change, what about
s.num 1 as suggested by Cornelia ?
I just tried and gcc optimizes
s.num != 0 s.num != 1 to s.num 1
The former will be more readable once we
replace 0 and 1 with defines.
So ignore my advice, keep code as is but use defines.
+ return -EINVAL;
+
+ vq-user_be = s.num;
+
+ return 0;
+}
+
+static long vhost_get_vring_big_endian(struct vhost_virtqueue *vq, u32
idx,
+int __user *argp)
+{
+ struct vhost_vring_state s = {
+ .index = idx,
+ .num = vq-user_be
+ };
+
+ if (copy_to_user(argp, s, sizeof(s)))
+ return -EFAULT;
+
+ return 0;
+}
+#else
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+int __user *argp)
+{
+ return -ENOIOCTLCMD;
+}
+
+static long vhost_get_vring_big_endian(struct vhost_virtqueue *vq, u32
idx,
+
Re: [PATCH v4 7/8] vhost: feature to set the vring endianness
On Fri, Apr 10, 2015 at 12:19:16PM +0200, Greg Kurz wrote:
This patch brings cross-endian support to vhost when used to implement
legacy virtio devices. Since it is a relatively rare situation, the
feature availability is controlled by a kernel config option (not set
by default).
The vq-is_le boolean field is added to cache the endianness to be
used for ring accesses. It defaults to native endian, as expected
by legacy virtio devices. When the ring gets active, we force little
endian if the device is modern. When the ring is deactivated, we
revert to the native endian default.
If cross-endian was compiled in, a vq-user_be boolean field is added
so that userspace may request a specific endianness. This field is
used to override the default when activating the ring of a legacy
device. It has no effect on modern devices.
Signed-off-by: Greg Kurz gk...@linux.vnet.ibm.com
---
drivers/vhost/Kconfig | 10 ++
drivers/vhost/vhost.c | 76
+++-
drivers/vhost/vhost.h | 12 +--
include/uapi/linux/vhost.h |9 +
4 files changed, 103 insertions(+), 4 deletions(-)
Changes since v3:
- VHOST_SET_VRING_ENDIAN_LEGACY ioctl renamed to VHOST_SET_VRING_BIG_ENDIAN
- ioctl API is now: 0 for le, 1 for be, other values are EINVAL
- ioctl doesn't filter out modern devices
- ioctl stubs return ENOIOCTLCMD
- forbid endianness changes when vring is active
- logic now handled with vq-is_le and vq-user_be according to device
start/stop as suggested by Michael
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 017a1e8..0aec88c 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -32,3 +32,13 @@ config VHOST
---help---
This option is selected by any driver which needs to access
the core of vhost.
+
+config VHOST_SET_ENDIAN_LEGACY
I'd prefer namin this VHOST_CROSS_ENDIAN_LEGACY
+ bool Cross-endian support for host kernel accelerator
+ default n
+ ---help---
+ This option allows vhost to support guests with a different byte
+ ordering from host. It is disabled by default since it adds overhead
+ and it is only needed by a few platforms (powerpc and arm).
and is only useful on a few platforms (powerpc and arm).
it seems to refer to overhead, which is rarely needed.
needed is a bit too strong, you can always e.g. run virtio
in userspace.
+
+ If unsure, say N.
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2ee2826..3eb756b 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -199,6 +199,10 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq-call = NULL;
vq-log_ctx = NULL;
vq-memory = NULL;
+ vq-is_le = virtio_legacy_is_little_endian();
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+ vq-user_be = !vq-is_le;
+#endif
add a wrapper for this too?
}
static int vhost_worker(void *data)
@@ -630,6 +634,53 @@ static long vhost_set_memory(struct vhost_dev *d, struct
vhost_memory __user *m)
return 0;
}
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+int __user *argp)
+{
+ struct vhost_vring_state s;
+
+ if (vq-private_data)
+ return -EBUSY;
+
+ if (copy_from_user(s, argp, sizeof(s)))
+ return -EFAULT;
+
+ if (s.num s.num != 1)
s.num ~0x1
+ return -EINVAL;
+
+ vq-user_be = s.num;
+
+ return 0;
+}
+
+static long vhost_get_vring_big_endian(struct vhost_virtqueue *vq, u32 idx,
+int __user *argp)
+{
+ struct vhost_vring_state s = {
+ .index = idx,
+ .num = vq-user_be
+ };
+
+ if (copy_to_user(argp, s, sizeof(s)))
+ return -EFAULT;
+
+ return 0;
+}
+#else
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+int __user *argp)
+{
+ return -ENOIOCTLCMD;
+}
+
+static long vhost_get_vring_big_endian(struct vhost_virtqueue *vq, u32 idx,
+int __user *argp)
+{
+ return -ENOIOCTLCMD;
+}
+#endif /* CONFIG_VHOST_SET_ENDIAN_LEGACY */
+
long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
{
struct file *eventfp, *filep = NULL;
@@ -806,6 +857,12 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl,
void __user *argp)
} else
filep = eventfp;
break;
+ case VHOST_SET_VRING_BIG_ENDIAN:
+ r = vhost_set_vring_big_endian(vq, argp);
+ break;
+ case VHOST_GET_VRING_BIG_ENDIAN:
+ r = vhost_get_vring_big_endian(vq, idx, argp);
+ break;
default:
r = -ENOIOCTLCMD;
}
@@ -1040,12 +1097,29 @@ static int
Re: [PATCH v4 7/8] vhost: feature to set the vring endianness
On Tue, 21 Apr 2015 16:04:23 +0200
Michael S. Tsirkin m...@redhat.com wrote:
On Fri, Apr 10, 2015 at 12:19:16PM +0200, Greg Kurz wrote:
This patch brings cross-endian support to vhost when used to implement
legacy virtio devices. Since it is a relatively rare situation, the
feature availability is controlled by a kernel config option (not set
by default).
The vq-is_le boolean field is added to cache the endianness to be
used for ring accesses. It defaults to native endian, as expected
by legacy virtio devices. When the ring gets active, we force little
endian if the device is modern. When the ring is deactivated, we
revert to the native endian default.
If cross-endian was compiled in, a vq-user_be boolean field is added
so that userspace may request a specific endianness. This field is
used to override the default when activating the ring of a legacy
device. It has no effect on modern devices.
Signed-off-by: Greg Kurz gk...@linux.vnet.ibm.com
---
drivers/vhost/Kconfig | 10 ++the
drivers/vhost/vhost.c | 76
+++-
drivers/vhost/vhost.h | 12 +--
include/uapi/linux/vhost.h |9 +
4 files changed, 103 insertions(+), 4 deletions(-)
Changes since v3:
- VHOST_SET_VRING_ENDIAN_LEGACY ioctl renamed to VHOST_SET_VRING_BIG_ENDIAN
- ioctl API is now: 0 for le, 1 for be, other values are EINVAL
- ioctl doesn't filter out modern devices
- ioctl stubs return ENOIOCTLCMD
- forbid endianness changes when vring is active
- logic now handled with vq-is_le and vq-user_be according to device
start/stop as suggested by Michael
diff --git a/drivers/vhost/Kconfig b/drivers/vhost/Kconfig
index 017a1e8..0aec88c 100644
--- a/drivers/vhost/Kconfig
+++ b/drivers/vhost/Kconfig
@@ -32,3 +32,13 @@ config VHOST
---help---
This option is selected by any driver which needs to access
the core of vhost.
+
+config VHOST_SET_ENDIAN_LEGACY
I'd prefer namin this VHOST_CROSS_ENDIAN_LEGACY
Yes, makes sense. I'll make sure most of the cross-endian changes are
easy to grep.
+ bool Cross-endian support for host kernel accelerator
+ default n
+ ---help---
+ This option allows vhost to support guests with a different byte
+ ordering from host. It is disabled by default since it adds overhead
+ and it is only needed by a few platforms (powerpc and arm).
and is only useful on a few platforms (powerpc and arm).
it seems to refer to overhead, which is rarely needed.
needed is a bit too strong, you can always e.g. run virtio
in userspace.
My poor English again... it seems you understood what I wanted to
write though :)
+
+ If unsure, say N.
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2ee2826..3eb756b 100644the
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -199,6 +199,10 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq-call = NULL;
vq-log_ctx = NULL;
vq-memory = NULL;
+ vq-is_le = virtio_legacy_is_little_endian();
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+ vq-user_be = !vq-is_le;
+#endif
add a wrapper for this too?
Will do.
}
static int vhost_worker(void *data)
@@ -630,6 +634,53 @@ static long vhost_set_memory(struct vhost_dev *d,
struct vhost_memory __user *m)
return 0;
}
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+ int __user *argp)
+{
+ struct vhost_vring_state s;
+
+ if (vq-private_data)
+ return -EBUSY;
+
+ if (copy_from_user(s, argp, sizeof(s)))
+ return -EFAULT;
+
+ if (s.num s.num != 1)
s.num ~0x1
Since s.num is unsigned and I assume this won't change, what about
s.num 1 as suggested by Cornelia ?
+ return -EINVAL;
+
+ vq-user_be = s.num;
+
+ return 0;
+}
+
+static long vhost_get_vring_big_endian(struct vhost_virtqueue *vq, u32 idx,
+ int __user *argp)
+{
+ struct vhost_vring_state s = {
+ .index = idx,
+ .num = vq-user_be
+ };
+
+ if (copy_to_user(argp, s, sizeof(s)))
+ return -EFAULT;
+
+ return 0;
+}
+#else
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+ int __user *argp)
+{
+ return -ENOIOCTLCMD;
+}
+
+static long vhost_get_vring_big_endian(struct vhost_virtqueue *vq, u32 idx,
+ int __user *argp)
+{
+ return -ENOIOCTLCMD;
+}
+#endif /* CONFIG_VHOST_SET_ENDIAN_LEGACY */
+
long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
{
struct file *eventfp, *filep = NULL;
@@ -806,6 +857,12 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl,
void __user *argp)
Re: [PATCH v4 7/8] vhost: feature to set the vring endianness
On Tue, 14 Apr 2015 16:20:23 +0200
Cornelia Huck cornelia.h...@de.ibm.com wrote:
On Fri, 10 Apr 2015 12:19:16 +0200
Greg Kurz gk...@linux.vnet.ibm.com wrote:
This patch brings cross-endian support to vhost when used to implement
legacy virtio devices. Since it is a relatively rare situation, the
feature availability is controlled by a kernel config option (not set
by default).
The vq-is_le boolean field is added to cache the endianness to be
used for ring accesses. It defaults to native endian, as expected
by legacy virtio devices. When the ring gets active, we force little
endian if the device is modern. When the ring is deactivated, we
revert to the native endian default.
If cross-endian was compiled in, a vq-user_be boolean field is added
so that userspace may request a specific endianness. This field is
used to override the default when activating the ring of a legacy
device. It has no effect on modern devices.
Signed-off-by: Greg Kurz gk...@linux.vnet.ibm.com
---
drivers/vhost/Kconfig | 10 ++
drivers/vhost/vhost.c | 76
+++-
drivers/vhost/vhost.h | 12 +--
include/uapi/linux/vhost.h |9 +
4 files changed, 103 insertions(+), 4 deletions(-)
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+ int __user *argp)
+{
+ struct vhost_vring_state s;
+
+ if (vq-private_data)
+ return -EBUSY;
+
+ if (copy_from_user(s, argp, sizeof(s)))
+ return -EFAULT;
+
+ if (s.num s.num != 1)
Checking for s.num 1 might be more obvious at a glance?
Sure since s.num is unsigned.
+ return -EINVAL;
+
+ vq-user_be = s.num;
+
+ return 0;
+}
+
(...)
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static void vhost_init_is_le(struct vhost_virtqueue *vq)
+{
+ vq-is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq-user_be;
So if the endianness is not explicitly set to BE, it will be forced to
LE (instead of native endian)? Won't that break userspace that does not
yet use the new interface when CONFIG_VHOST_SET_ENDIAN_LEGACY is set?
If userspace doesn't use the new interface, then vq-user_be will retain its
default value that was set in vhost_vq_reset(), i.e. :
vq-user_be = !virtio_legacy_is_little_endian();
This means default is native endian.
What about adding this comment ?
static void vhost_init_is_le(struct vhost_virtqueue *vq)
{
/* Note for legacy virtio: user_be is initialized in vhost_vq_reset()
* according to the host endianness. If userspace does not set an
* explicit endianness, the default behavior is native endian, as
* expected by legacy virtio.
*/
vq-is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq-user_be;
}
+}
+#else
+static void vhost_init_is_le(struct vhost_virtqueue *vq)
+{
+ if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
+ vq-is_le = true;
+}
+#endif
+
int vhost_init_used(struct vhost_virtqueue *vq)
{
__virtio16 last_used_idx;
int r;
- if (!vq-private_data)
+ if (!vq-private_data) {
+ vq-is_le = virtio_legacy_is_little_endian();
return 0;
+ }
+
+ vhost_init_is_le(vq);
r = vhost_update_used_flags(vq);
if (r)
--
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Re: [PATCH v4 7/8] vhost: feature to set the vring endianness
On Tue, 14 Apr 2015 17:13:52 +0200
Greg Kurz gk...@linux.vnet.ibm.com wrote:
On Tue, 14 Apr 2015 16:20:23 +0200
Cornelia Huck cornelia.h...@de.ibm.com wrote:
On Fri, 10 Apr 2015 12:19:16 +0200
Greg Kurz gk...@linux.vnet.ibm.com wrote:
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static void vhost_init_is_le(struct vhost_virtqueue *vq)
+{
+ vq-is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq-user_be;
So if the endianness is not explicitly set to BE, it will be forced to
LE (instead of native endian)? Won't that break userspace that does not
yet use the new interface when CONFIG_VHOST_SET_ENDIAN_LEGACY is set?
If userspace doesn't use the new interface, then vq-user_be will retain its
default value that was set in vhost_vq_reset(), i.e. :
vq-user_be = !virtio_legacy_is_little_endian();
This means default is native endian.
What about adding this comment ?
static void vhost_init_is_le(struct vhost_virtqueue *vq)
{
/* Note for legacy virtio: user_be is initialized in vhost_vq_reset()
* according to the host endianness. If userspace does not set an
* explicit endianness, the default behavior is native endian, as
* expected by legacy virtio.
*/
Good idea, as this is easy to miss.
vq-is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq-user_be;
}
+}
+#else
+static void vhost_init_is_le(struct vhost_virtqueue *vq)
+{
+ if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
+ vq-is_le = true;
+}
+#endif
+
int vhost_init_used(struct vhost_virtqueue *vq)
{
__virtio16 last_used_idx;
int r;
- if (!vq-private_data)
+ if (!vq-private_data) {
+ vq-is_le = virtio_legacy_is_little_endian();
return 0;
+ }
+
+ vhost_init_is_le(vq);
r = vhost_update_used_flags(vq);
if (r)
--
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Re: [PATCH v4 7/8] vhost: feature to set the vring endianness
On Fri, 10 Apr 2015 12:19:16 +0200
Greg Kurz gk...@linux.vnet.ibm.com wrote:
This patch brings cross-endian support to vhost when used to implement
legacy virtio devices. Since it is a relatively rare situation, the
feature availability is controlled by a kernel config option (not set
by default).
The vq-is_le boolean field is added to cache the endianness to be
used for ring accesses. It defaults to native endian, as expected
by legacy virtio devices. When the ring gets active, we force little
endian if the device is modern. When the ring is deactivated, we
revert to the native endian default.
If cross-endian was compiled in, a vq-user_be boolean field is added
so that userspace may request a specific endianness. This field is
used to override the default when activating the ring of a legacy
device. It has no effect on modern devices.
Signed-off-by: Greg Kurz gk...@linux.vnet.ibm.com
---
drivers/vhost/Kconfig | 10 ++
drivers/vhost/vhost.c | 76
+++-
drivers/vhost/vhost.h | 12 +--
include/uapi/linux/vhost.h |9 +
4 files changed, 103 insertions(+), 4 deletions(-)
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static long vhost_set_vring_big_endian(struct vhost_virtqueue *vq,
+int __user *argp)
+{
+ struct vhost_vring_state s;
+
+ if (vq-private_data)
+ return -EBUSY;
+
+ if (copy_from_user(s, argp, sizeof(s)))
+ return -EFAULT;
+
+ if (s.num s.num != 1)
Checking for s.num 1 might be more obvious at a glance?
+ return -EINVAL;
+
+ vq-user_be = s.num;
+
+ return 0;
+}
+
(...)
+#ifdef CONFIG_VHOST_SET_ENDIAN_LEGACY
+static void vhost_init_is_le(struct vhost_virtqueue *vq)
+{
+ vq-is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq-user_be;
So if the endianness is not explicitly set to BE, it will be forced to
LE (instead of native endian)? Won't that break userspace that does not
yet use the new interface when CONFIG_VHOST_SET_ENDIAN_LEGACY is set?
+}
+#else
+static void vhost_init_is_le(struct vhost_virtqueue *vq)
+{
+ if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
+ vq-is_le = true;
+}
+#endif
+
int vhost_init_used(struct vhost_virtqueue *vq)
{
__virtio16 last_used_idx;
int r;
- if (!vq-private_data)
+ if (!vq-private_data) {
+ vq-is_le = virtio_legacy_is_little_endian();
return 0;
+ }
+
+ vhost_init_is_le(vq);
r = vhost_update_used_flags(vq);
if (r)
--
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