[RESEND PATCH v5 0/1] docs: driver-api: virtio: virtio on Linux

[RESEND PATCH v5 0/1] docs: driver-api: virtio: virtio on Linux

[Ricardo Cañuelo]

Basic documentation about virtio in the kernel and a small tutorial for
virtio drivers.

Tested on kernel/git/mst/vhost.git (linux-next)

Changes in v5:
  - remove already merged patch
  - grammar fixes
  - clarify some API details
  - rework example code

Changes in v4:
  - reword the intro paragraphs
  - grammar fixes

Changes in v3:
  - fix commit message in patch 1
  - minor additional fixes to virtio kerneldocs
  - use proper Sphinx markup for links to references

Changes in v2:
  - virtio spec links updated to v1.2
  - simplify virtio.rst and remove most low level parts that are
    already covered by the spec
  - split the kerneldocs fixes to a separate patch
  - remove :c:func: rst formatting

Ricardo Cañuelo (1):
  docs: driver-api: virtio: virtio on Linux

 Documentation/driver-api/index.rst            |   1 +
 Documentation/driver-api/virtio/index.rst     |  11 +
 Documentation/driver-api/virtio/virtio.rst    | 144 +++++++++++++
 .../virtio/writing_virtio_drivers.rst         | 197 ++++++++++++++++++
 MAINTAINERS                                   |   1 +
 5 files changed, 354 insertions(+)
 create mode 100644 Documentation/driver-api/virtio/index.rst
 create mode 100644 Documentation/driver-api/virtio/virtio.rst
 create mode 100644 Documentation/driver-api/virtio/writing_virtio_drivers.rst

-- 
2.25.1

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[RESEND PATCH v5 1/1] docs: driver-api: virtio: virtio on Linux

[Ricardo Cañuelo]

Basic doc about Virtio on Linux and a short tutorial on Virtio drivers.

Signed-off-by: Ricardo Cañuelo <ricardo.canuelo@collabora.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
---
 Documentation/driver-api/index.rst            |   1 +
 Documentation/driver-api/virtio/index.rst     |  11 +
 Documentation/driver-api/virtio/virtio.rst    | 144 +++++++++++++
 .../virtio/writing_virtio_drivers.rst         | 197 ++++++++++++++++++
 MAINTAINERS                                   |   1 +
 5 files changed, 354 insertions(+)
 create mode 100644 Documentation/driver-api/virtio/index.rst
 create mode 100644 Documentation/driver-api/virtio/virtio.rst
 create mode 100644 Documentation/driver-api/virtio/writing_virtio_drivers.rst

diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst
index d3a58f77328e..30a3de452b1d 100644
--- a/Documentation/driver-api/index.rst
+++ b/Documentation/driver-api/index.rst
@@ -106,6 +106,7 @@ available subsections can be seen below.
    vfio-mediated-device
    vfio
    vfio-pci-device-specific-driver-acceptance
+   virtio/index
    xilinx/index
    xillybus
    zorro
diff --git a/Documentation/driver-api/virtio/index.rst b/Documentation/driver-api/virtio/index.rst
new file mode 100644
index 000000000000..528b14b291e3
--- /dev/null
+++ b/Documentation/driver-api/virtio/index.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======
+Virtio
+======
+
+.. toctree::
+   :maxdepth: 1
+
+   virtio
+   writing_virtio_drivers
diff --git a/Documentation/driver-api/virtio/virtio.rst b/Documentation/driver-api/virtio/virtio.rst
new file mode 100644
index 000000000000..921758fc3b23
--- /dev/null
+++ b/Documentation/driver-api/virtio/virtio.rst
@@ -0,0 +1,144 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _virtio:
+
+===============
+Virtio on Linux
+===============
+
+Introduction
+============
+
+Virtio is an open standard that defines a protocol for communication
+between drivers and devices of different types, see Chapter 5 ("Device
+Types") of the virtio spec `[1]`_. Originally developed as a standard
+for paravirtualized devices implemented by a hypervisor, it can be used
+to interface any compliant device (real or emulated) with a driver.
+
+For illustrative purposes, this document will focus on the common case
+of a Linux kernel running in a virtual machine and using paravirtualized
+devices provided by the hypervisor, which exposes them as virtio devices
+via standard mechanisms such as PCI.
+
+
+Device - Driver communication: virtqueues
+=========================================
+
+Although the virtio devices are really an abstraction layer in the
+hypervisor, they're exposed to the guest as if they are physical devices
+using a specific transport method -- PCI, MMIO or CCW -- that is
+orthogonal to the device itself. The virtio spec defines these transport
+methods in detail, including device discovery, capabilities and
+interrupt handling.
+
+The communication between the driver in the guest OS and the device in
+the hypervisor is done through shared memory (that's what makes virtio
+devices so efficient) using specialized data structures called
+virtqueues, which are actually ring buffers [#f1]_ of buffer descriptors
+similar to the ones used in a network device:
+
+.. kernel-doc:: include/uapi/linux/virtio_ring.h
+    :identifiers: struct vring_desc
+
+All the buffers the descriptors point to are allocated by the guest and
+used by the host either for reading or for writing but not for both.
+
+Refer to Chapter 2.5 ("Virtqueues") of the virtio spec `[1]`_ for the
+reference definitions of virtqueues and to `[2]`_ for an illustrated
+overview of how the host device and the guest driver communicate.
+
+The :c:type:`vring_virtqueue` struct models a virtqueue, including the
+ring buffers and management data. Embedded in this struct is the
+:c:type:`virtqueue` struct, which is the data structure that's
+ultimately used by virtio drivers:
+
+.. kernel-doc:: include/linux/virtio.h
+    :identifiers: struct virtqueue
+
+The callback function pointed by this struct is triggered when the
+device has consumed the buffers provided by the driver. More
+specifically, the trigger will be an interrupt issued by the hypervisor
+(see vring_interrupt()). Interrupt request handlers are registered for
+a virtqueue during the virtqueue setup process (transport-specific).
+
+.. kernel-doc:: drivers/virtio/virtio_ring.c
+    :identifiers: vring_interrupt
+
+
+Device discovery and probing
+============================
+
+In the kernel, the virtio core contains the virtio bus driver and
+transport-specific drivers like `virtio-pci` and `virtio-mmio`. Then
+there are individual virtio drivers for specific device types that are
+registered to the virtio bus driver.
+
+How a virtio device is found and configured by the kernel depends on how
+the hypervisor defines it. Taking the `QEMU virtio-console
+<https://gitlab.com/qemu-project/qemu/-/blob/master/hw/char/virtio-console.c>`__
+device as an example. When using PCI as a transport method, the device
+will present itself on the PCI bus with vendor 0x1af4 (Red Hat, Inc.)
+and device id 0x1003 (virtio console), as defined in the spec, so the
+kernel will detect it as it would do with any other PCI device.
+
+During the PCI enumeration process, if a device is found to match the
+virtio-pci driver (according to the virtio-pci device table, any PCI
+device with vendor id = 0x1af4)::
+
+	/* Qumranet donated their vendor ID for devices 0x1000 thru 0x10FF. */
+	static const struct pci_device_id virtio_pci_id_table[] = {
+		{ PCI_DEVICE(PCI_VENDOR_ID_REDHAT_QUMRANET, PCI_ANY_ID) },
+		{ 0 }
+	};
+
+then the virtio-pci driver is probed and, if the probing goes well, the
+device is registered to the virtio bus::
+
+	static int virtio_pci_probe(struct pci_dev *pci_dev,
+				    const struct pci_device_id *id)
+	{
+		...
+
+		if (force_legacy) {
+			rc = virtio_pci_legacy_probe(vp_dev);
+			/* Also try modern mode if we can't map BAR0 (no IO space). */
+			if (rc == -ENODEV || rc == -ENOMEM)
+				rc = virtio_pci_modern_probe(vp_dev);
+			if (rc)
+				goto err_probe;
+		} else {
+			rc = virtio_pci_modern_probe(vp_dev);
+			if (rc == -ENODEV)
+				rc = virtio_pci_legacy_probe(vp_dev);
+			if (rc)
+				goto err_probe;
+		}
+
+		...
+
+		rc = register_virtio_device(&vp_dev->vdev);
+
+When the device is registered to the virtio bus the kernel will look
+for a driver in the bus that can handle the device and call that
+driver's ``probe`` method.
+
+It's at this stage that the virtqueues will be allocated and configured
+by calling the appropriate ``virtio_find`` helper function, such as
+virtio_find_single_vq() or virtio_find_vqs(), which will end up
+calling a transport-specific ``find_vqs`` method.
+
+
+References
+==========
+
+_`[1]` Virtio Spec v1.2:
+https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
+
+Check for later versions of the spec as well.
+
+_`[2]` Virtqueues and virtio ring: How the data travels
+https://www.redhat.com/en/blog/virtqueues-and-virtio-ring-how-data-travels
+
+.. rubric:: Footnotes
+
+.. [#f1] that's why they may be also referred to as virtrings.
diff --git a/Documentation/driver-api/virtio/writing_virtio_drivers.rst b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
new file mode 100644
index 000000000000..e14c58796d25
--- /dev/null
+++ b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
@@ -0,0 +1,197 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _writing_virtio_drivers:
+
+======================
+Writing Virtio Drivers
+======================
+
+Introduction
+============
+
+This document serves as a basic guideline for driver programmers that
+need to hack a new virtio driver or understand the essentials of the
+existing ones. See :ref:`Virtio on Linux <virtio>` for a general
+overview of virtio.
+
+
+Driver boilerplate
+==================
+
+As a bare minimum, a virtio driver needs to register in the virtio bus
+and configure the virtqueues for the device according to its spec, the
+configuration of the virtqueues in the driver side must match the
+virtqueue definitions in the device. A basic driver skeleton could look
+like this::
+
+	#include <linux/virtio.h>
+	#include <linux/virtio_ids.h>
+	#include <linux/virtio_config.h>
+	#include <linux/module.h>
+
+	/* device private data (one per device) */
+	struct virtio_dummy_dev {
+		struct virtqueue *vq;
+	};
+
+	static void virtio_dummy_recv_cb(struct virtqueue *vq)
+	{
+		struct virtio_dummy_dev *dev = vq->vdev->priv;
+		char *buf;
+		unsigned int len;
+
+		while ((buf = virtqueue_get_buf(dev->vq, &len)) != NULL) {
+			/* process the received data */
+		}
+	}
+
+	static int virtio_dummy_probe(struct virtio_device *vdev)
+	{
+		struct virtio_dummy_dev *dev = NULL;
+
+		/* initialize device data */
+		dev = kzalloc(sizeof(struct virtio_dummy_dev), GFP_KERNEL);
+		if (!dev)
+			return -ENOMEM;
+
+		/* the device has a single virtqueue */
+		dev->vq = virtio_find_single_vq(vdev, virtio_dummy_recv_cb, "input");
+		if (IS_ERR(dev->vq)) {
+			kfree(dev);
+			return PTR_ERR(dev->vq);
+
+		}
+		vdev->priv = dev;
+
+		/* from this point on, the device can notify and get callbacks */
+		virtio_device_ready(vdev);
+
+		return 0;
+	}
+
+	static void virtio_dummy_remove(struct virtio_device *vdev)
+	{
+		struct virtio_dummy_dev *dev = vdev->priv;
+
+		/*
+		 * disable vq interrupts: equivalent to
+		 * vdev->config->reset(vdev)
+		 */
+		virtio_reset_device(vdev);
+
+		/* detach unused buffers */
+		while ((buf = virtqueue_detach_unused_buf(dev->vq)) != NULL) {
+			kfree(buf);
+		}
+
+		/* remove virtqueues */
+		vdev->config->del_vqs(vdev);
+
+		kfree(dev);
+	}
+
+	static const struct virtio_device_id id_table[] = {
+		{ VIRTIO_ID_DUMMY, VIRTIO_DEV_ANY_ID },
+		{ 0 },
+	};
+
+	static struct virtio_driver virtio_dummy_driver = {
+		.driver.name =  KBUILD_MODNAME,
+		.driver.owner = THIS_MODULE,
+		.id_table =     id_table,
+		.probe =        virtio_dummy_probe,
+		.remove =       virtio_dummy_remove,
+	};
+
+	module_virtio_driver(virtio_dummy_driver);
+	MODULE_DEVICE_TABLE(virtio, id_table);
+	MODULE_DESCRIPTION("Dummy virtio driver");
+	MODULE_LICENSE("GPL");
+
+The device id ``VIRTIO_ID_DUMMY`` here is a placeholder, virtio drivers
+should be added only for devices that are defined in the spec, see
+include/uapi/linux/virtio_ids.h. Device ids need to be at least reserved
+in the virtio spec before being added to that file.
+
+If your driver doesn't have to do anything special in its ``init`` and
+``exit`` methods, you can use the module_virtio_driver() helper to
+reduce the amount of boilerplate code.
+
+The ``probe`` method does the minimum driver setup in this case
+(memory allocation for the device data) and initializes the
+virtqueue. virtio_device_ready() is used to enable the virtqueue and to
+notify the device that the driver is ready to manage the device
+("DRIVER_OK"). The virtqueues are anyway enabled automatically by the
+core after ``probe`` returns.
+
+.. kernel-doc:: include/linux/virtio_config.h
+    :identifiers: virtio_device_ready
+
+In any case, the virtqueues need to be enabled before adding buffers to
+them.
+
+Sending and receiving data
+==========================
+
+The virtio_dummy_recv_cb() callback in the code above will be triggered
+when the device notifies the driver after it finishes processing a
+descriptor or descriptor chain, either for reading or writing. However,
+that's only the second half of the virtio device-driver communication
+process, as the communication is always started by the driver regardless
+of the direction of the data transfer.
+
+To configure a buffer transfer from the driver to the device, first you
+have to add the buffers -- packed as `scatterlists` -- to the
+appropriate virtqueue using any of the virtqueue_add_inbuf(),
+virtqueue_add_outbuf() or virtqueue_add_sgs(), depending on whether you
+need to add one input `scatterlist` (for the device to fill in), one
+output `scatterlist` (for the device to consume) or multiple
+`scatterlists`, respectively. Then, once the virtqueue is set up, a call
+to virtqueue_kick() sends a notification that will be serviced by the
+hypervisor that implements the device::
+
+	struct scatterlist sg[1];
+	sg_init_one(sg, buffer, BUFLEN);
+	virtqueue_add_inbuf(dev->vq, sg, 1, buffer, GFP_ATOMIC);
+	virtqueue_kick(dev->vq);
+
+.. kernel-doc:: drivers/virtio/virtio_ring.c
+    :identifiers: virtqueue_add_inbuf
+
+.. kernel-doc:: drivers/virtio/virtio_ring.c
+    :identifiers: virtqueue_add_outbuf
+
+.. kernel-doc:: drivers/virtio/virtio_ring.c
+    :identifiers: virtqueue_add_sgs
+
+Then, after the device has read or written the buffers prepared by the
+driver and notifies it back, the driver can call virtqueue_get_buf() to
+read the data produced by the device (if the virtqueue was set up with
+input buffers) or simply to reclaim the buffers if they were already
+consumed by the device:
+
+.. kernel-doc:: drivers/virtio/virtio_ring.c
+    :identifiers: virtqueue_get_buf_ctx
+
+The virtqueue callbacks can be disabled and re-enabled using the
+virtqueue_disable_cb() and the family of virtqueue_enable_cb() functions
+respectively. See drivers/virtio/virtio_ring.c for more details:
+
+.. kernel-doc:: drivers/virtio/virtio_ring.c
+    :identifiers: virtqueue_disable_cb
+
+.. kernel-doc:: drivers/virtio/virtio_ring.c
+    :identifiers: virtqueue_enable_cb
+
+But note that some spurious callbacks can still be triggered under
+certain scenarios. The way to disable callbacks reliably is to reset the
+device or the virtqueue (virtio_reset_device()).
+
+
+References
+==========
+
+_`[1]` Virtio Spec v1.2:
+https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
+
+Check for later versions of the spec as well.
diff --git a/MAINTAINERS b/MAINTAINERS
index 8a5012ba6ff9..ec59f1189d46 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -21476,6 +21476,7 @@ S:	Maintained
 F:	Documentation/ABI/testing/sysfs-bus-vdpa
 F:	Documentation/ABI/testing/sysfs-class-vduse
 F:	Documentation/devicetree/bindings/virtio/
+F:	Documentation/driver-api/virtio/
 F:	drivers/block/virtio_blk.c
 F:	drivers/crypto/virtio/
 F:	drivers/net/virtio_net.c
-- 
2.25.1

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Re: [RESEND PATCH v5 1/1] docs: driver-api: virtio: virtio on Linux

[Cornelia Huck]

On Mon, Oct 10 2022, Bagas Sanjaya <bagasdotme@gmail.com> wrote:

> On Mon, Oct 10, 2022 at 08:43:59AM +0200, Ricardo Cañuelo wrote:
>> +
>> +References
>> +==========
>> +
>> +_`[1]` Virtio Spec v1.2:
>> +https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>> +
>> +Check for later versions of the spec as well.
>> +
>
> The version checking should be made comment (not visible on the output):
>
> ---- >8 ----
> diff --git a/Documentation/driver-api/virtio/virtio.rst b/Documentation/driver-api/virtio/virtio.rst
> index 70b3aa6bcf5518..4f3abbec4e8b2c 100644
> --- a/Documentation/driver-api/virtio/virtio.rst
> +++ b/Documentation/driver-api/virtio/virtio.rst
> @@ -134,7 +134,7 @@ References
>  _`[1]` Virtio Spec v1.2:
>  https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>  
> -Check for later versions of the spec as well.
> +.. Check for later versions of the spec as well.
>  
>  _`[2]` Virtqueues and virtio ring: How the data travels
>  https://www.redhat.com/en/blog/virtqueues-and-virtio-ring-how-data-travels
>
>> diff --git a/Documentation/driver-api/virtio/writing_virtio_drivers.rst b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>> new file mode 100644
>> index 000000000000..e14c58796d25
>> --- /dev/null
>> +++ b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>> <snipped>...
>> +References
>> +==========
>> +
>> +_`[1]` Virtio Spec v1.2:
>> +https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>> +
>> +Check for later versions of the spec as well.
>
> Same reply.

I don't think we should hide that in a comment -- unless you want to
update this file every time a new version of the virtio spec gets
released.

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Re: [RESEND PATCH v5 1/1] docs: driver-api: virtio: virtio on Linux

[Michael S. Tsirkin]

On Mon, Oct 10, 2022 at 03:43:46PM +0200, Cornelia Huck wrote:
> On Mon, Oct 10 2022, Bagas Sanjaya <bagasdotme@gmail.com> wrote:
> 
> > On Mon, Oct 10, 2022 at 08:43:59AM +0200, Ricardo Cañuelo wrote:
> >> +
> >> +References
> >> +==========
> >> +
> >> +_`[1]` Virtio Spec v1.2:
> >> +https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
> >> +
> >> +Check for later versions of the spec as well.
> >> +
> >
> > The version checking should be made comment (not visible on the output):
> >
> > ---- >8 ----
> > diff --git a/Documentation/driver-api/virtio/virtio.rst b/Documentation/driver-api/virtio/virtio.rst
> > index 70b3aa6bcf5518..4f3abbec4e8b2c 100644
> > --- a/Documentation/driver-api/virtio/virtio.rst
> > +++ b/Documentation/driver-api/virtio/virtio.rst
> > @@ -134,7 +134,7 @@ References
> >  _`[1]` Virtio Spec v1.2:
> >  https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
> >  
> > -Check for later versions of the spec as well.
> > +.. Check for later versions of the spec as well.
> >  
> >  _`[2]` Virtqueues and virtio ring: How the data travels
> >  https://www.redhat.com/en/blog/virtqueues-and-virtio-ring-how-data-travels
> >
> >> diff --git a/Documentation/driver-api/virtio/writing_virtio_drivers.rst b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
> >> new file mode 100644
> >> index 000000000000..e14c58796d25
> >> --- /dev/null
> >> +++ b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
> >> <snipped>...
> >> +References
> >> +==========
> >> +
> >> +_`[1]` Virtio Spec v1.2:
> >> +https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
> >> +
> >> +Check for later versions of the spec as well.
> >
> > Same reply.
> 
> I don't think we should hide that in a comment -- unless you want to
> update this file every time a new version of the virtio spec gets
> released.

What do you suggest? Just http://docs.oasis-open.org/virtio/virtio/ ?

-- 
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Re: [RESEND PATCH v5 1/1] docs: driver-api: virtio: virtio on Linux

[Cornelia Huck]

On Mon, Oct 10 2022, "Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Mon, Oct 10, 2022 at 03:43:46PM +0200, Cornelia Huck wrote:
>> On Mon, Oct 10 2022, Bagas Sanjaya <bagasdotme@gmail.com> wrote:
>> 
>> > On Mon, Oct 10, 2022 at 08:43:59AM +0200, Ricardo Cañuelo wrote:
>> >> +
>> >> +References
>> >> +==========
>> >> +
>> >> +_`[1]` Virtio Spec v1.2:
>> >> +https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>> >> +
>> >> +Check for later versions of the spec as well.
>> >> +
>> >
>> > The version checking should be made comment (not visible on the output):
>> >
>> > ---- >8 ----
>> > diff --git a/Documentation/driver-api/virtio/virtio.rst b/Documentation/driver-api/virtio/virtio.rst
>> > index 70b3aa6bcf5518..4f3abbec4e8b2c 100644
>> > --- a/Documentation/driver-api/virtio/virtio.rst
>> > +++ b/Documentation/driver-api/virtio/virtio.rst
>> > @@ -134,7 +134,7 @@ References
>> >  _`[1]` Virtio Spec v1.2:
>> >  https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>> >  
>> > -Check for later versions of the spec as well.
>> > +.. Check for later versions of the spec as well.
>> >  
>> >  _`[2]` Virtqueues and virtio ring: How the data travels
>> >  https://www.redhat.com/en/blog/virtqueues-and-virtio-ring-how-data-travels
>> >
>> >> diff --git a/Documentation/driver-api/virtio/writing_virtio_drivers.rst b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>> >> new file mode 100644
>> >> index 000000000000..e14c58796d25
>> >> --- /dev/null
>> >> +++ b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>> >> <snipped>...
>> >> +References
>> >> +==========
>> >> +
>> >> +_`[1]` Virtio Spec v1.2:
>> >> +https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>> >> +
>> >> +Check for later versions of the spec as well.
>> >
>> > Same reply.
>> 
>> I don't think we should hide that in a comment -- unless you want to
>> update this file every time a new version of the virtio spec gets
>> released.
>
> What do you suggest? Just http://docs.oasis-open.org/virtio/virtio/ ?

That one is ugly, as it is just a directory listing... my preference is
to link to the latest version at the time of writing, and mentioning
that there may be later versions available, i.e. what the patch does
right now.

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Re: [RESEND PATCH v5 1/1] docs: driver-api: virtio: virtio on Linux

[Cornelia Huck]

On Tue, Oct 11 2022, Bagas Sanjaya <bagasdotme@gmail.com> wrote:

> On 10/11/22 13:51, Cornelia Huck wrote:
>> On Mon, Oct 10 2022, "Michael S. Tsirkin" <mst@redhat.com> wrote:
>> 
>>> On Mon, Oct 10, 2022 at 03:43:46PM +0200, Cornelia Huck wrote:
>>>> On Mon, Oct 10 2022, Bagas Sanjaya <bagasdotme@gmail.com> wrote:
>>>>
>>>>> On Mon, Oct 10, 2022 at 08:43:59AM +0200, Ricardo Cañuelo wrote:
>>>>>> +
>>>>>> +References
>>>>>> +==========
>>>>>> +
>>>>>> +_`[1]` Virtio Spec v1.2:
>>>>>> +https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>>>>>> +
>>>>>> +Check for later versions of the spec as well.
>>>>>> +
>>>>>
>>>>> The version checking should be made comment (not visible on the output):
>>>>>
>>>>> ---- >8 ----
>>>>> diff --git a/Documentation/driver-api/virtio/virtio.rst b/Documentation/driver-api/virtio/virtio.rst
>>>>> index 70b3aa6bcf5518..4f3abbec4e8b2c 100644
>>>>> --- a/Documentation/driver-api/virtio/virtio.rst
>>>>> +++ b/Documentation/driver-api/virtio/virtio.rst
>>>>> @@ -134,7 +134,7 @@ References
>>>>>  _`[1]` Virtio Spec v1.2:
>>>>>  https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>>>>>  
>>>>> -Check for later versions of the spec as well.
>>>>> +.. Check for later versions of the spec as well.
>>>>>  
>>>>>  _`[2]` Virtqueues and virtio ring: How the data travels
>>>>>  https://www.redhat.com/en/blog/virtqueues-and-virtio-ring-how-data-travels
>>>>>
>>>>>> diff --git a/Documentation/driver-api/virtio/writing_virtio_drivers.rst b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>>>>>> new file mode 100644
>>>>>> index 000000000000..e14c58796d25
>>>>>> --- /dev/null
>>>>>> +++ b/Documentation/driver-api/virtio/writing_virtio_drivers.rst
>>>>>> <snipped>...
>>>>>> +References
>>>>>> +==========
>>>>>> +
>>>>>> +_`[1]` Virtio Spec v1.2:
>>>>>> +https://docs.oasis-open.org/virtio/virtio/v1.2/virtio-v1.2.html
>>>>>> +
>>>>>> +Check for later versions of the spec as well.
>>>>>
>>>>> Same reply.
>>>>
>>>> I don't think we should hide that in a comment -- unless you want to
>>>> update this file every time a new version of the virtio spec gets
>>>> released.
>>>
>>> What do you suggest? Just http://docs.oasis-open.org/virtio/virtio/ ?
>> 
>> That one is ugly, as it is just a directory listing... my preference is
>> to link to the latest version at the time of writing, and mentioning
>> that there may be later versions available, i.e. what the patch does
>> right now.
>> 
>
> IMO, we can link to current spec version and update it as newer version
> becomes public; without adding "check for later version" comment note.

Is it really that important to update? Unless the virtio innards change
radically, looking at an older version is likely to be sufficient.

["We should update it" is likely to become "Oh, we should have updated
it some time ago" IME :)]

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Re: [RESEND PATCH v5 1/1] docs: driver-api: virtio: virtio on Linux

[Ricardo Cañuelo]

Hi Bagas, thanks for the review, some comments below:

On lun, oct 10 2022 at 20:04:14, Bagas Sanjaya <bagasdotme@gmail.com> wrote:

> What link is for [2]? I think you'll need to spell out the link title.
> Also, the external reference pointers should be parenthesized to indicate
> that these are references:

That's a matter of personal opinion and I disagree with it. There's no
consensus across the kernel docs and I'm using the IEEE style, which is
fairly standard.


>  The :c:type:`vring_virtqueue` struct models a virtqueue, including the
>  ring buffers and management data. Embedded in this struct is the
>
>
> Personally speaking, ReST citations should do the job better (these
> links are external references, right?).

I don't want to use a full ReST code reference for that, as that struct
is not really part of the interface for virtio drivers and its
definition is an implementation detail. But I still want to have it
properly formatted in the html and pdf outputs, that's why I'm using
:c:type: there.


>> +It's at this stage that the virtqueues will be allocated and configured
>> +by calling the appropriate ``virtio_find`` helper function, such as
>> +virtio_find_single_vq() or virtio_find_vqs(), which will end up
>> +calling a transport-specific ``find_vqs`` method.
>> +
>
> Looks like the wording at the beginning confuses me, so better say:
>
> ---- >8 ----
> diff --git a/Documentation/driver-api/virtio/virtio.rst b/Documentation/driver-api/virtio/virtio.rst
> index 07fd2d7c51e689..7947b4ca690efd 100644
> --- a/Documentation/driver-api/virtio/virtio.rst
> +++ b/Documentation/driver-api/virtio/virtio.rst
> @@ -123,10 +123,10 @@ When the device is registered to the virtio bus the kernel will look
>  for a driver in the bus that can handle the device and call that
>  driver's ``probe`` method.

I think this is a matter of style as well, maybe a native speaker can
pitch in about the correctness of it.

Cheers,
Ricardo
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Re: [RESEND PATCH v5 1/1] docs: driver-api: virtio: virtio on Linux

[Michael S. Tsirkin]

On Tue, Oct 11, 2022 at 10:46:43AM +0200, Ricardo Cañuelo wrote:
> >> +It's at this stage that the virtqueues will be allocated and configured
> >> +by calling the appropriate ``virtio_find`` helper function, such as
> >> +virtio_find_single_vq() or virtio_find_vqs(), which will end up
> >> +calling a transport-specific ``find_vqs`` method.
> >> +
> >
> > Looks like the wording at the beginning confuses me, so better say:
> >
> > ---- >8 ----
> > diff --git a/Documentation/driver-api/virtio/virtio.rst b/Documentation/driver-api/virtio/virtio.rst
> > index 07fd2d7c51e689..7947b4ca690efd 100644
> > --- a/Documentation/driver-api/virtio/virtio.rst
> > +++ b/Documentation/driver-api/virtio/virtio.rst
> > @@ -123,10 +123,10 @@ When the device is registered to the virtio bus the kernel will look
> >  for a driver in the bus that can handle the device and call that
> >  driver's ``probe`` method.
> 
> I think this is a matter of style as well, maybe a native speaker can
> pitch in about the correctness of it.
> 
> Cheers,
> Ricardo

I think I agree with this comment.  This seems minor enough so I applied
the patch for now. Bagas would you like to post your suggestion as a patch on
top? Would be appreciated. Thanks!

-- 
MST

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Re: [RESEND PATCH v5 1/1] docs: driver-api: virtio: virtio on Linux

[Michael S. Tsirkin]

On Mon, Dec 19, 2022 at 03:38:11PM +0700, Bagas Sanjaya wrote:
> On 12/19/22 13:20, Michael S. Tsirkin wrote:
> > I think I agree with this comment.  This seems minor enough so I applied
> > the patch for now. Bagas would you like to post your suggestion as a patch on
> > top? Would be appreciated. Thanks!
> > 
> 
> I don't see the patch applied on your tree [1], or applied to where? Or
> even forget to push?
> 
> Thanks.
> 
> [1]: https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/

Here:

https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/log/?h=linux-next

> -- 
> An old man doll... just what I always wanted! - Clara

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