[v6,2/3] virtio-dmabuf: introduce virtio-dmabuf

This API manages objects (in this iteration,
dmabuf fds) that can be shared along different
virtio devices, associated to a UUID.

The API allows the different devices to add,
remove and/or retrieve the objects by simply
invoking the public functions that reside in the
virtio-dmabuf file.

For vhost backends, the API stores the pointer
to the backend holding the object.

Suggested-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
 MAINTAINERS                       |   7 ++
 hw/display/meson.build            |   1 +
 hw/display/virtio-dmabuf.c        | 134 +++++++++++++++++++++++++++++
 include/hw/virtio/virtio-dmabuf.h | 103 ++++++++++++++++++++++
 tests/unit/meson.build            |   1 +
 tests/unit/test-virtio-dmabuf.c   | 137 ++++++++++++++++++++++++++++++
 6 files changed, 383 insertions(+)
 create mode 100644 hw/display/virtio-dmabuf.c
 create mode 100644 include/hw/virtio/virtio-dmabuf.h
 create mode 100644 tests/unit/test-virtio-dmabuf.c

On Wed, Sep 6, 2023 at 1:15 PM Albert Esteve <aesteve@redhat.com> wrote:

> This API manages objects (in this iteration,
> dmabuf fds) that can be shared along different
> virtio devices, associated to a UUID.
>
> The API allows the different devices to add,
> remove and/or retrieve the objects by simply
> invoking the public functions that reside in the
> virtio-dmabuf file.
>
> For vhost backends, the API stores the pointer
> to the backend holding the object.
>
> Suggested-by: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
>  MAINTAINERS                       |   7 ++
>  hw/display/meson.build            |   1 +
>  hw/display/virtio-dmabuf.c        | 134 +++++++++++++++++++++++++++++
>  include/hw/virtio/virtio-dmabuf.h | 103 ++++++++++++++++++++++
>  tests/unit/meson.build            |   1 +
>  tests/unit/test-virtio-dmabuf.c   | 137 ++++++++++++++++++++++++++++++
>  6 files changed, 383 insertions(+)
>  create mode 100644 hw/display/virtio-dmabuf.c
>  create mode 100644 include/hw/virtio/virtio-dmabuf.h
>  create mode 100644 tests/unit/test-virtio-dmabuf.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 3b29568ed4..fb0f7b823f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2150,6 +2150,13 @@ T: git https://gitlab.com/cohuck/qemu.git s390-next
>  T: git https://github.com/borntraeger/qemu.git s390-next
>  L: qemu-s390x@nongnu.org
>
> +virtio-dmabuf
> +M: Albert Esteve <aesteve@redhat.com>
> +S: Supported
> +F: hw/display/virtio-dmabuf.c
> +F: include/hw/virtio/virtio-dmabuf.h
> +F: tests/unit/test-virtio-dmabuf.c
> +
>  virtiofs
>  M: Stefan Hajnoczi <stefanha@redhat.com>
>  S: Supported
> diff --git a/hw/display/meson.build b/hw/display/meson.build
> index 413ba4ab24..05619c6968 100644
> --- a/hw/display/meson.build
> +++ b/hw/display/meson.build
> @@ -37,6 +37,7 @@ system_ss.add(when: 'CONFIG_MACFB', if_true:
> files('macfb.c'))
>  system_ss.add(when: 'CONFIG_NEXTCUBE', if_true: files('next-fb.c'))
>
>  system_ss.add(when: 'CONFIG_VGA', if_true: files('vga.c'))
> +system_ss.add(when: 'CONFIG_VIRTIO', if_true: files('virtio-dmabuf.c'))
>
>  if (config_all_devices.has_key('CONFIG_VGA_CIRRUS') or
>      config_all_devices.has_key('CONFIG_VGA_PCI') or
> diff --git a/hw/display/virtio-dmabuf.c b/hw/display/virtio-dmabuf.c
> new file mode 100644
> index 0000000000..268ffe81ec
> --- /dev/null
> +++ b/hw/display/virtio-dmabuf.c
> @@ -0,0 +1,134 @@
> +/*
> + * Virtio Shared dma-buf
> + *
> + * Copyright Red Hat, Inc. 2023
> + *
> + * Authors:
> + *     Albert Esteve <aesteve@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or
> later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "hw/virtio/virtio-dmabuf.h"
> +
> +
> +static GMutex lock;
> +static GHashTable *resource_uuids;
> +
> +/*
> + * uuid_equal_func: wrapper for UUID is_equal function to
> + * satisfy g_hash_table_new expected parameters signatures.
> + */
> +static int uuid_equal_func(const void *lhv, const void *rhv)
> +{
> +    return qemu_uuid_is_equal(lhv, rhv);
> +}
> +
> +static bool virtio_add_resource(QemuUUID *uuid, VirtioSharedObject *value)
> +{
> +    bool result;
> +    g_mutex_lock(&lock);
> +    if (resource_uuids == NULL) {
> +        resource_uuids = g_hash_table_new_full(
> +            qemu_uuid_hash, uuid_equal_func, NULL, g_free);
> +    }
> +    if (g_hash_table_lookup(resource_uuids, uuid) != NULL) {
> +        g_mutex_unlock(&lock);
> +        return false;
> +    }
> +    result = g_hash_table_insert(resource_uuids, uuid, value);
> +    g_mutex_unlock(&lock);
> +
> +    return result;
> +}
> +
> +bool virtio_add_dmabuf(QemuUUID *uuid, int udmabuf_fd)
> +{
> +    bool result;
> +    VirtioSharedObject *vso;
> +    if (udmabuf_fd < 0) {
> +        return false;
> +    }
> +    vso = g_new(VirtioSharedObject, 1);
> +    vso->type = TYPE_DMABUF;
> +    vso->value = GINT_TO_POINTER(udmabuf_fd);
> +    result = virtio_add_resource(uuid, vso);
> +
> +    return result;
>

Just realized that the result variable is not required anymore
with the last change.

Not sure if it is worth sending a new review for this...
I can take it into account for a follow-up refactor for the next
update I make on the file. Or just send a separate trivial patch.


> +}
> +
> +bool virtio_add_vhost_device(QemuUUID *uuid, struct vhost_dev *dev)
> +{
> +    bool result;
> +    VirtioSharedObject *vso;
> +    if (dev == NULL) {
> +        return false;
> +    }
> +    vso = g_new(VirtioSharedObject, 1);
> +    vso->type = TYPE_VHOST_DEV;
> +    vso->value = dev;
> +    result = virtio_add_resource(uuid, vso);
> +
> +    return result;
> +}
> +
> +bool virtio_remove_resource(const QemuUUID *uuid)
> +{
> +    bool result;
> +    g_mutex_lock(&lock);
> +    result = g_hash_table_remove(resource_uuids, uuid);
> +    g_mutex_unlock(&lock);
> +
> +    return result;
> +}
> +
> +static VirtioSharedObject *get_shared_object(const QemuUUID *uuid)
> +{
> +    g_mutex_lock(&lock);
> +    if (resource_uuids == NULL) {
> +        g_mutex_unlock(&lock);
> +        return NULL;
> +    }
> +    gpointer lookup_res = g_hash_table_lookup(resource_uuids, uuid);
> +    g_mutex_unlock(&lock);
> +    return (VirtioSharedObject*) lookup_res;
> +}
> +
> +int virtio_lookup_dmabuf(const QemuUUID *uuid)
> +{
> +    VirtioSharedObject *vso = get_shared_object(uuid);
> +    if (vso == NULL) {
> +        return -1;
> +    }
> +    assert(vso->type == TYPE_DMABUF);
> +    return GPOINTER_TO_INT(vso->value);
> +}
> +
> +struct vhost_dev *virtio_lookup_vhost_device(const QemuUUID *uuid)
> +{
> +    VirtioSharedObject *vso = get_shared_object(uuid);
> +    if (vso == NULL) {
> +        return NULL;
> +    }
> +    assert(vso->type == TYPE_VHOST_DEV);
> +    return (struct vhost_dev *) vso->value;
> +}
> +
> +SharedObjectType virtio_object_type(const QemuUUID *uuid)
> +{
> +    VirtioSharedObject *vso = get_shared_object(uuid);
> +    if (vso == NULL) {
> +        return TYPE_INVALID;
> +    }
> +    return vso->type;
> +}
> +
> +void virtio_free_resources(void)
> +{
> +    g_mutex_lock(&lock);
> +    g_hash_table_destroy(resource_uuids);
> +    /* Reference count shall be 0 after the implicit unref on destroy */
> +    resource_uuids = NULL;
> +    g_mutex_unlock(&lock);
> +}
> diff --git a/include/hw/virtio/virtio-dmabuf.h
> b/include/hw/virtio/virtio-dmabuf.h
> new file mode 100644
> index 0000000000..202eec5868
> --- /dev/null
> +++ b/include/hw/virtio/virtio-dmabuf.h
> @@ -0,0 +1,103 @@
> +/*
> + * Virtio Shared dma-buf
> + *
> + * Copyright Red Hat, Inc. 2023
> + *
> + * Authors:
> + *     Albert Esteve <aesteve@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#ifndef VIRTIO_DMABUF_H
> +#define VIRTIO_DMABUF_H
> +
> +#include "qemu/osdep.h"
> +
> +#include <glib.h>
> +#include "qemu/uuid.h"
> +#include "vhost.h"
> +
> +typedef enum SharedObjectType {
> +    TYPE_INVALID = 0,
> +    TYPE_DMABUF,
> +    TYPE_VHOST_DEV,
> +} SharedObjectType;
> +
> +typedef struct VirtioSharedObject {
> +    SharedObjectType type;
> +    gpointer value;
> +} VirtioSharedObject;
> +
> +/**
> + * virtio_add_dmabuf() - Add a new dma-buf resource to the lookup table
> + * @uuid: new resource's UUID
> + * @dmabuf_fd: the dma-buf descriptor that will be stored and shared with
> + *             other virtio devices. The caller retains ownership over the
> + *             descriptor and its lifecycle.
> + *
> + * Note: @dmabuf_fd must be a valid (non-negative) file descriptor.
> + *
> + * Return: true if the UUID did not exist and the resource has been added,
> + * false if another resource with the same UUID already existed.
> + * Note that if it finds a repeated UUID, the resource is not inserted in
> + * the lookup table.
> + */
> +bool virtio_add_dmabuf(QemuUUID *uuid, int dmabuf_fd);
> +
> +/**
> + * virtio_add_vhost_device() - Add a new exporter vhost device that holds
> the
> + * resource with the associated UUID
> + * @uuid: new resource's UUID
> + * @dev: the pointer to the vhost device that holds the resource. The
> caller
> + *       retains ownership over the device struct and its lifecycle.
> + *
> + * Return: true if the UUID did not exist and the device has been tracked,
> + * false if another resource with the same UUID already existed.
> + * Note that if it finds a repeated UUID, the resource is not inserted in
> + * the lookup table.
> + */
> +bool virtio_add_vhost_device(QemuUUID *uuid, struct vhost_dev *dev);
> +
> +/**
> + * virtio_remove_resource() - Removes a resource from the lookup table
> + * @uuid: resource's UUID
> + *
> + * Return: true if the UUID has been found and removed from the lookup
> table.
> + */
> +bool virtio_remove_resource(const QemuUUID *uuid);
> +
> +/**
> + * virtio_lookup_dmabuf() - Looks for a dma-buf resource in the lookup
> table
> + * @uuid: resource's UUID
> + *
> + * Return: the dma-buf file descriptor integer, or -1 if the key is not
> found.
> + */
> +int virtio_lookup_dmabuf(const QemuUUID *uuid);
> +
> +/**
> + * virtio_lookup_vhost_device() - Looks for an exporter vhost device in
> the
> + * lookup table
> + * @uuid: resource's UUID
> + *
> + * Return: pointer to the vhost_dev struct, or NULL if the key is not
> found.
> + */
> +struct vhost_dev *virtio_lookup_vhost_device(const QemuUUID *uuid);
> +
> +/**
> + * virtio_object_type() - Looks for the type of resource in the lookup
> table
> + * @uuid: resource's UUID
> + *
> + * Return: the type of resource associated with the UUID, or TYPE_INVALID
> if
> + * the key is not found.
> + */
> +SharedObjectType virtio_object_type(const QemuUUID *uuid);
> +
> +/**
> + * virtio_free_resources() - Destroys all keys and values of the shared
> + * resources lookup table, and frees them
> + */
> +void virtio_free_resources(void);
> +
> +#endif /* VIRTIO_DMABUF_H */
> diff --git a/tests/unit/meson.build b/tests/unit/meson.build
> index 93977cc32d..425ecc30fb 100644
> --- a/tests/unit/meson.build
> +++ b/tests/unit/meson.build
> @@ -50,6 +50,7 @@ tests = {
>    'test-qapi-util': [],
>    'test-interval-tree': [],
>    'test-xs-node': [qom],
> +  'test-virtio-dmabuf': [meson.project_source_root() /
> 'hw/display/virtio-dmabuf.c'],
>  }
>
>  if have_system or have_tools
> diff --git a/tests/unit/test-virtio-dmabuf.c
> b/tests/unit/test-virtio-dmabuf.c
> new file mode 100644
> index 0000000000..40fe262538
> --- /dev/null
> +++ b/tests/unit/test-virtio-dmabuf.c
> @@ -0,0 +1,137 @@
> +/*
> + * QEMU tests for shared dma-buf API
> + *
> + * Copyright (c) 2023 Red Hat, Inc.
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, see <
> http://www.gnu.org/licenses/>.
> + *
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/virtio/virtio-dmabuf.h"
> +
> +
> +static void test_add_remove_resources(void)
> +{
> +    QemuUUID uuid;
> +    int i, dmabuf_fd;
> +
> +    for (i = 0; i < 100; ++i) {
> +        qemu_uuid_generate(&uuid);
> +        dmabuf_fd = g_random_int_range(3, 500);
> +        /* Add a new resource */
> +        g_assert(virtio_add_dmabuf(&uuid, dmabuf_fd));
> +        g_assert_cmpint(virtio_lookup_dmabuf(&uuid), ==, dmabuf_fd);
> +        /* Remove the resource */
> +        g_assert(virtio_remove_resource(&uuid));
> +        /* Resource is not found anymore */
> +        g_assert_cmpint(virtio_lookup_dmabuf(&uuid), ==, -1);
> +    }
> +}
> +
> +static void test_add_remove_dev(void)
> +{
> +    QemuUUID uuid;
> +    struct vhost_dev *dev = g_new0(struct vhost_dev, 1);
> +    int i;
> +
> +    for (i = 0; i < 100; ++i) {
> +        qemu_uuid_generate(&uuid);
> +        virtio_add_vhost_device(&uuid, dev);
> +        /* vhost device is found */
> +        g_assert(virtio_lookup_vhost_device(&uuid) != NULL);
> +        /* Remove the vhost device */
> +        g_assert(virtio_remove_resource(&uuid));
> +        /* vhost device is not found anymore */
> +        g_assert(virtio_lookup_vhost_device(&uuid) == NULL);
> +    }
> +    g_free(dev);
> +}
> +
> +static void test_remove_invalid_resource(void)
> +{
> +    QemuUUID uuid;
> +    int i;
> +
> +    for (i = 0; i < 20; ++i) {
> +        qemu_uuid_generate(&uuid);
> +        g_assert_cmpint(virtio_lookup_dmabuf(&uuid), ==, -1);
> +        /* Removing a resource that does not exist returns false */
> +        g_assert_false(virtio_remove_resource(&uuid));
> +    }
> +}
> +
> +static void test_add_invalid_resource(void)
> +{
> +    QemuUUID uuid;
> +    struct vhost_dev *dev = NULL;
> +    int i, dmabuf_fd = -2, alt_dmabuf = 2;
> +
> +    for (i = 0; i < 20; ++i) {
> +        qemu_uuid_generate(&uuid);
> +        /* Add a new resource with invalid (negative) resource fd */
> +        g_assert_false(virtio_add_dmabuf(&uuid, dmabuf_fd));
> +        /* Resource is not found */
> +        g_assert_cmpint(virtio_lookup_dmabuf(&uuid), ==, -1);
> +        /* Add a new vhost device with invalid (NULL) pointer */
> +        g_assert_false(virtio_add_vhost_device(&uuid, dev));
> +        /* vhost device is not found */
> +        g_assert(virtio_lookup_vhost_device(&uuid) == NULL);
> +    }
> +
> +    for (i = 0; i < 20; ++i) {
> +        /* Add a valid resource */
> +        qemu_uuid_generate(&uuid);
> +        dmabuf_fd = g_random_int_range(3, 500);
> +        g_assert(virtio_add_dmabuf(&uuid, dmabuf_fd));
> +        g_assert_cmpint(virtio_lookup_dmabuf(&uuid), ==, dmabuf_fd);
> +        /* Add a new resource with repeated uuid returns false */
> +        g_assert_false(virtio_add_dmabuf(&uuid, alt_dmabuf));
> +        /* The value for the uuid key is not replaced */
> +        g_assert_cmpint(virtio_lookup_dmabuf(&uuid), ==, dmabuf_fd);
> +    }
> +}
> +
> +static void test_free_resources(void)
> +{
> +    QemuUUID uuids[20];
> +    int i, dmabuf_fd;
> +
> +    for (i = 0; i < ARRAY_SIZE(uuids); ++i) {
> +        qemu_uuid_generate(&uuids[i]);
> +        dmabuf_fd = g_random_int_range(3, 500);
> +        g_assert(virtio_add_dmabuf(&uuids[i], dmabuf_fd));
> +        g_assert_cmpint(virtio_lookup_dmabuf(&uuids[i]), ==, dmabuf_fd);
> +    }
> +    virtio_free_resources();
> +    for (i = 0; i < ARRAY_SIZE(uuids); ++i) {
> +        /* None of the resources is found after free'd */
> +        g_assert_cmpint(virtio_lookup_dmabuf(&uuids[i]), ==, -1);
> +    }
> +
> +}
> +
> +int main(int argc, char **argv)
> +{
> +    g_test_init(&argc, &argv, NULL);
> +    g_test_add_func("/virtio-dmabuf/add_rm_res",
> test_add_remove_resources);
> +        g_test_add_func("/virtio-dmabuf/add_rm_dev", test_add_remove_dev);
> +    g_test_add_func("/virtio-dmabuf/rm_invalid_res",
> +                    test_remove_invalid_resource);
> +    g_test_add_func("/virtio-dmabuf/add_invalid_res",
> +                    test_add_invalid_resource);
> +    g_test_add_func("/virtio-dmabuf/free_res", test_free_resources);
> +
> +    return g_test_run();
> +}
> --
> 2.41.0
>
>

On 6/9/23 13:15, Albert Esteve wrote:
> This API manages objects (in this iteration,
> dmabuf fds) that can be shared along different
> virtio devices, associated to a UUID.
> 
> The API allows the different devices to add,
> remove and/or retrieve the objects by simply
> invoking the public functions that reside in the
> virtio-dmabuf file.
> 
> For vhost backends, the API stores the pointer
> to the backend holding the object.
> 
> Suggested-by: Gerd Hoffmann <kraxel@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
>   MAINTAINERS                       |   7 ++
>   hw/display/meson.build            |   1 +
>   hw/display/virtio-dmabuf.c        | 134 +++++++++++++++++++++++++++++
>   include/hw/virtio/virtio-dmabuf.h | 103 ++++++++++++++++++++++
>   tests/unit/meson.build            |   1 +
>   tests/unit/test-virtio-dmabuf.c   | 137 ++++++++++++++++++++++++++++++
>   6 files changed, 383 insertions(+)
>   create mode 100644 hw/display/virtio-dmabuf.c
>   create mode 100644 include/hw/virtio/virtio-dmabuf.h
>   create mode 100644 tests/unit/test-virtio-dmabuf.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 3b29568ed4..fb0f7b823f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2150,6 +2150,13 @@ T: git https://gitlab.com/cohuck/qemu.git s390-next
>   T: git https://github.com/borntraeger/qemu.git s390-next
>   L: qemu-s390x@nongnu.org
>   
> +virtio-dmabuf
> +M: Albert Esteve <aesteve@redhat.com>
> +S: Supported
> +F: hw/display/virtio-dmabuf.c
> +F: include/hw/virtio/virtio-dmabuf.h
> +F: tests/unit/test-virtio-dmabuf.c
> +
>   virtiofs
>   M: Stefan Hajnoczi <stefanha@redhat.com>
>   S: Supported
> diff --git a/hw/display/meson.build b/hw/display/meson.build
> index 413ba4ab24..05619c6968 100644
> --- a/hw/display/meson.build
> +++ b/hw/display/meson.build
> @@ -37,6 +37,7 @@ system_ss.add(when: 'CONFIG_MACFB', if_true: files('macfb.c'))
>   system_ss.add(when: 'CONFIG_NEXTCUBE', if_true: files('next-fb.c'))
>   
>   system_ss.add(when: 'CONFIG_VGA', if_true: files('vga.c'))
> +system_ss.add(when: 'CONFIG_VIRTIO', if_true: files('virtio-dmabuf.c'))
>   
>   if (config_all_devices.has_key('CONFIG_VGA_CIRRUS') or
>       config_all_devices.has_key('CONFIG_VGA_PCI') or
> diff --git a/hw/display/virtio-dmabuf.c b/hw/display/virtio-dmabuf.c
> new file mode 100644
> index 0000000000..268ffe81ec
> --- /dev/null
> +++ b/hw/display/virtio-dmabuf.c
> @@ -0,0 +1,134 @@
> +/*
> + * Virtio Shared dma-buf
> + *
> + * Copyright Red Hat, Inc. 2023
> + *
> + * Authors:
> + *     Albert Esteve <aesteve@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + */
> +
> +#include "hw/virtio/virtio-dmabuf.h"
> +
> +
> +static GMutex lock;
> +static GHashTable *resource_uuids;
> +
> +/*
> + * uuid_equal_func: wrapper for UUID is_equal function to
> + * satisfy g_hash_table_new expected parameters signatures.
> + */
> +static int uuid_equal_func(const void *lhv, const void *rhv)
> +{
> +    return qemu_uuid_is_equal(lhv, rhv);
> +}
> +
> +static bool virtio_add_resource(QemuUUID *uuid, VirtioSharedObject *value)
> +{
> +    bool result;
> +    g_mutex_lock(&lock);
> +    if (resource_uuids == NULL) {
> +        resource_uuids = g_hash_table_new_full(
> +            qemu_uuid_hash, uuid_equal_func, NULL, g_free);
> +    }
> +    if (g_hash_table_lookup(resource_uuids, uuid) != NULL) {
> +        g_mutex_unlock(&lock);
> +        return false;
> +    }
> +    result = g_hash_table_insert(resource_uuids, uuid, value);
> +    g_mutex_unlock(&lock);
> +
> +    return result;
> +}

Alternatively same logic, but simpler / safer:

static bool virtio_add_resource(...)
{
     bool result = false;

     g_mutex_lock(&lock);
     if (resource_uuids == NULL) {
         resource_uuids = g_hash_table_new_full(qemu_uuid_hash,
                                                uuid_equal_func,
                                                NULL,
                                                g_free);
     }
     if (g_hash_table_lookup(resource_uuids, uuid) == NULL) {
        result = g_hash_table_insert(resource_uuids, uuid, value);
     }
     g_mutex_unlock(&lock);

     return result;
}

> +static VirtioSharedObject *get_shared_object(const QemuUUID *uuid)
> +{
> +    g_mutex_lock(&lock);
> +    if (resource_uuids == NULL) {
> +        g_mutex_unlock(&lock);
> +        return NULL;
> +    }
> +    gpointer lookup_res = g_hash_table_lookup(resource_uuids, uuid);
> +    g_mutex_unlock(&lock);
> +    return (VirtioSharedObject*) lookup_res;
> +}

Similarly:

static VirtioSharedObject *get_shared_object(const QemuUUID *uuid)
{
     gpointer lookup_res = NULL;

     g_mutex_lock(&lock);
     if (resource_uuids != NULL) {
         lookup_res = g_hash_table_lookup(resource_uuids, uuid);
     }
     g_mutex_unlock(&lock);

     return (VirtioSharedObject *)lookup_res;
}

> +int main(int argc, char **argv)
> +{
> +    g_test_init(&argc, &argv, NULL);
> +    g_test_add_func("/virtio-dmabuf/add_rm_res", test_add_remove_resources);
> +        g_test_add_func("/virtio-dmabuf/add_rm_dev", test_add_remove_dev);

Mis-indent.

> +    g_test_add_func("/virtio-dmabuf/rm_invalid_res",
> +                    test_remove_invalid_resource);
> +    g_test_add_func("/virtio-dmabuf/add_invalid_res",
> +                    test_add_invalid_resource);
> +    g_test_add_func("/virtio-dmabuf/free_res", test_free_resources);
> +
> +    return g_test_run();
> +}

Thanks for updating, LGTM!

On Wed, Sep 6, 2023 at 4:21 PM Philippe Mathieu-Daudé <philmd@linaro.org>
wrote:

> On 6/9/23 13:15, Albert Esteve wrote:
> > This API manages objects (in this iteration,
> > dmabuf fds) that can be shared along different
> > virtio devices, associated to a UUID.
> >
> > The API allows the different devices to add,
> > remove and/or retrieve the objects by simply
> > invoking the public functions that reside in the
> > virtio-dmabuf file.
> >
> > For vhost backends, the API stores the pointer
> > to the backend holding the object.
> >
> > Suggested-by: Gerd Hoffmann <kraxel@redhat.com>
> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
> > ---
> >   MAINTAINERS                       |   7 ++
> >   hw/display/meson.build            |   1 +
> >   hw/display/virtio-dmabuf.c        | 134 +++++++++++++++++++++++++++++
> >   include/hw/virtio/virtio-dmabuf.h | 103 ++++++++++++++++++++++
> >   tests/unit/meson.build            |   1 +
> >   tests/unit/test-virtio-dmabuf.c   | 137 ++++++++++++++++++++++++++++++
> >   6 files changed, 383 insertions(+)
> >   create mode 100644 hw/display/virtio-dmabuf.c
> >   create mode 100644 include/hw/virtio/virtio-dmabuf.h
> >   create mode 100644 tests/unit/test-virtio-dmabuf.c
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 3b29568ed4..fb0f7b823f 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -2150,6 +2150,13 @@ T: git https://gitlab.com/cohuck/qemu.git
> s390-next
> >   T: git https://github.com/borntraeger/qemu.git s390-next
> >   L: qemu-s390x@nongnu.org
> >
> > +virtio-dmabuf
> > +M: Albert Esteve <aesteve@redhat.com>
> > +S: Supported
> > +F: hw/display/virtio-dmabuf.c
> > +F: include/hw/virtio/virtio-dmabuf.h
> > +F: tests/unit/test-virtio-dmabuf.c
> > +
> >   virtiofs
> >   M: Stefan Hajnoczi <stefanha@redhat.com>
> >   S: Supported
> > diff --git a/hw/display/meson.build b/hw/display/meson.build
> > index 413ba4ab24..05619c6968 100644
> > --- a/hw/display/meson.build
> > +++ b/hw/display/meson.build
> > @@ -37,6 +37,7 @@ system_ss.add(when: 'CONFIG_MACFB', if_true:
> files('macfb.c'))
> >   system_ss.add(when: 'CONFIG_NEXTCUBE', if_true: files('next-fb.c'))
> >
> >   system_ss.add(when: 'CONFIG_VGA', if_true: files('vga.c'))
> > +system_ss.add(when: 'CONFIG_VIRTIO', if_true: files('virtio-dmabuf.c'))
> >
> >   if (config_all_devices.has_key('CONFIG_VGA_CIRRUS') or
> >       config_all_devices.has_key('CONFIG_VGA_PCI') or
> > diff --git a/hw/display/virtio-dmabuf.c b/hw/display/virtio-dmabuf.c
> > new file mode 100644
> > index 0000000000..268ffe81ec
> > --- /dev/null
> > +++ b/hw/display/virtio-dmabuf.c
> > @@ -0,0 +1,134 @@
> > +/*
> > + * Virtio Shared dma-buf
> > + *
> > + * Copyright Red Hat, Inc. 2023
> > + *
> > + * Authors:
> > + *     Albert Esteve <aesteve@redhat.com>
> > + *
> > + * This work is licensed under the terms of the GNU GPL, version 2 or
> later.
> > + * See the COPYING file in the top-level directory.
> > + */
> > +
> > +#include "hw/virtio/virtio-dmabuf.h"
> > +
> > +
> > +static GMutex lock;
> > +static GHashTable *resource_uuids;
> > +
> > +/*
> > + * uuid_equal_func: wrapper for UUID is_equal function to
> > + * satisfy g_hash_table_new expected parameters signatures.
> > + */
> > +static int uuid_equal_func(const void *lhv, const void *rhv)
> > +{
> > +    return qemu_uuid_is_equal(lhv, rhv);
> > +}
> > +
> > +static bool virtio_add_resource(QemuUUID *uuid, VirtioSharedObject
> *value)
> > +{
> > +    bool result;
> > +    g_mutex_lock(&lock);
> > +    if (resource_uuids == NULL) {
> > +        resource_uuids = g_hash_table_new_full(
> > +            qemu_uuid_hash, uuid_equal_func, NULL, g_free);
> > +    }
> > +    if (g_hash_table_lookup(resource_uuids, uuid) != NULL) {
> > +        g_mutex_unlock(&lock);
> > +        return false;
> > +    }
> > +    result = g_hash_table_insert(resource_uuids, uuid, value);
> > +    g_mutex_unlock(&lock);
> > +
> > +    return result;
> > +}
>
> Alternatively same logic, but simpler / safer:
>
> static bool virtio_add_resource(...)
> {
>      bool result = false;
>
>      g_mutex_lock(&lock);
>      if (resource_uuids == NULL) {
>          resource_uuids = g_hash_table_new_full(qemu_uuid_hash,
>                                                 uuid_equal_func,
>                                                 NULL,
>                                                 g_free);
>      }
>      if (g_hash_table_lookup(resource_uuids, uuid) == NULL) {
>         result = g_hash_table_insert(resource_uuids, uuid, value);
>      }
>      g_mutex_unlock(&lock);
>
>      return result;
> }
>
> > +static VirtioSharedObject *get_shared_object(const QemuUUID *uuid)
> > +{
> > +    g_mutex_lock(&lock);
> > +    if (resource_uuids == NULL) {
> > +        g_mutex_unlock(&lock);
> > +        return NULL;
> > +    }
> > +    gpointer lookup_res = g_hash_table_lookup(resource_uuids, uuid);
> > +    g_mutex_unlock(&lock);
> > +    return (VirtioSharedObject*) lookup_res;
> > +}
>
> Similarly:
>
> static VirtioSharedObject *get_shared_object(const QemuUUID *uuid)
> {
>      gpointer lookup_res = NULL;
>
>      g_mutex_lock(&lock);
>      if (resource_uuids != NULL) {
>          lookup_res = g_hash_table_lookup(resource_uuids, uuid);
>      }
>      g_mutex_unlock(&lock);
>
>      return (VirtioSharedObject *)lookup_res;
> }
>
> > +int main(int argc, char **argv)
> > +{
> > +    g_test_init(&argc, &argv, NULL);
> > +    g_test_add_func("/virtio-dmabuf/add_rm_res",
> test_add_remove_resources);
> > +        g_test_add_func("/virtio-dmabuf/add_rm_dev",
> test_add_remove_dev);
>
> Mis-indent.
>
> > +    g_test_add_func("/virtio-dmabuf/rm_invalid_res",
> > +                    test_remove_invalid_resource);
> > +    g_test_add_func("/virtio-dmabuf/add_invalid_res",
> > +                    test_add_invalid_resource);
> > +    g_test_add_func("/virtio-dmabuf/free_res", test_free_resources);
> > +
> > +    return g_test_run();
> > +}
>
> Thanks for updating, LGTM!
>
> Suggestions look good, and is true that will lead to more safe and
maintanable code in the future,
if we add more branches where the mutex has to be handled.
I will send another revision then, thanks!