The vhost-user specification states that VHOST_USER_GET_QUEUE_NUM should
return the maximum number of queues supported by the back-end, not the
number of virtqueues. Since each queue pair consists of RX and TX
virtqueues, we need to divide VHOST_USER_MAX_QUEUES by 2 to get the
correct queue count.

Also rename VHOST_USER_MAX_QUEUES to VHOST_USER_MAX_VQS throughout the
codebase to better reflect that it represents the maximum number of
virtqueues, not queue pairs.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

This patch refactors the handling of vhost-user memory regions by
introducing a new `struct vdev_memory` to encapsulate the regions
array and their count (`nregions`) within the main `vu_dev` structure.

This new `vdev_memory` structure is then passed to the packet pool by
re-using the existing `p->buf` field. A `p->buf_size` of 0 indicates
that `p->buf` holds a pointer to `struct vdev_memory` instead of a
regular packet buffer. A new helper, `get_vdev_memory()`, is added to
abstract this access pattern.

Previous implementation was using a marker at the end of the memory
regions array. We can now uses all the slots.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

We always use imperative (no 'Returns:'), no tab after the ':' and
only one space, the first character is always lowercase.

This is fixed with:

 sed -i "s/Returns:/Return:/;s/Return:    /Return: /;s/Return:  */Return: /;s/Return: \([A-Z]\)/Return: \L\1/" *.[ch]

And manually updated to fix alignment of multiline comment and words
that must keep uppercase (like IPv4, TCP, UDP, Layer-4).

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Standardize and fix issues in `virtio.c` and `virtio.h` comment headers.

Improvements include:
- Added `()` to function names in comment summaries.
- Added colons after parameter and enum member tags.
- Changed `/*` to `/**` for `virtq_avail_event()` comment.
- Fixed typos (e.g., "file"->"fill", "virqueue"->"virtqueue").
- Added missing `Return:` tag for `vu_queue_rewind()`.
- Corrected parameter names in `virtio.h` comments to match code.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

vhost-user added several functions which are exposed in headers, but not
used outside the file where they're defined.  I can't tell if these are
really internal functions, or of they're logically supposed to be exported,
but we don't happen to have anything using them yet.

For the time being, just remove the exports.  We can add them back if we
need to.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Introduce facilities for guest migration on top of vhost-user
infrastructure.  Add migration facilities based on top of the current
vhost-user infrastructure, moving vu_migrate() and related functions
to migrate.c.

Versioned migration stages define function pointers to be called on
source or target, or data sections that need to be transferred.

The migration header consists of a magic number, a version number for the
encoding, and a "compat_version" which represents the oldest version which
is compatible with the current one.  We don't use it yet, but that allows
for the future possibility of backwards compatible protocol extensions.

Co-authored-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Set the file descriptor to use to transfer the
backend device state during migration.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
[sbrivio: Fixed nits and coding style here and there]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

After transferring the back-end’s internal state during migration,
check whether the back-end was able to successfully fully process
the state.

The value returned indicates success or error;
0 is success, any non-zero value is an error.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Sets logging shared memory space.

When the back-end has VHOST_USER_PROTOCOL_F_LOG_SHMFD protocol feature,
the log memory fd is provided in the ancillary data of
VHOST_USER_SET_LOG_BASE message, the size and offset of shared memory
area provided in the message.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
[sbrivio: Fix coding style in a bunch of places]
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

vu_dev will be needed to log page update.

Add the parameter to:

  vring_used_write()
  vu_queue_fill_by_index()
  vu_queue_fill()
  vring_used_idx_set()
  vu_queue_flush()

The new parameter is unused for now.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>