On Mon, Feb 17, 2025 at 05:40:04PM +0100, Albert Esteve wrote:
> Add SHMEM_MAP/UNMAP requests to vhost-user to
> handle VIRTIO Shared Memory mappings.
>
> This request allows backends to dynamically map
> fds into a VIRTIO Shared Memory Region indentified
> by its `shmid`. The map is performed by calling
> `memory_region_init_ram_from_fd` and adding the
> new region as a subregion of the shmem container
> MR. Then, the fd memory is advertised to the
> driver as a base addres + offset, so it can be
> read/written (depending on the mmap flags
> requested) while it is valid.
>
> The backend can unmap the memory range
> in a given VIRTIO Shared Memory Region (again,
> identified by its `shmid`), to free it.
> Upon receiving this message, the front-end
> must delete the MR as a subregion of
> the shmem container region and free its
> resources.
>
> Note that commit all these operations need
> to be delayed to after we respond the request
> to the backend to avoid deadlocks.
>
> The device model needs to create VirtSharedMemory
> instances for the VirtIO Shared Memory Regions
> and add them to the `VirtIODevice` instance.
>
> Signed-off-by: Albert Esteve <aest...@redhat.com>
> ---
> hw/virtio/vhost-user.c | 134 ++++++++++++++++++++++
> hw/virtio/virtio.c | 81 +++++++++++++
> include/hw/virtio/virtio.h | 27 +++++
> subprojects/libvhost-user/libvhost-user.c | 70 +++++++++++
> subprojects/libvhost-user/libvhost-user.h | 55 +++++++++
> 5 files changed, 367 insertions(+)
>
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 267b612587..d88e6f8c3c 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -115,6 +115,8 @@ typedef enum VhostUserBackendRequest {
> VHOST_USER_BACKEND_SHARED_OBJECT_ADD = 6,
> VHOST_USER_BACKEND_SHARED_OBJECT_REMOVE = 7,
> VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP = 8,
> + VHOST_USER_BACKEND_SHMEM_MAP = 9,
> + VHOST_USER_BACKEND_SHMEM_UNMAP = 10,
> VHOST_USER_BACKEND_MAX
> } VhostUserBackendRequest;
>
> @@ -192,6 +194,24 @@ typedef struct VhostUserShared {
> unsigned char uuid[16];
> } VhostUserShared;
>
> +/* For the flags field of VhostUserMMap */
> +#define VHOST_USER_FLAG_MAP_R (1u << 0)
> +#define VHOST_USER_FLAG_MAP_W (1u << 1)
> +
> +typedef struct {
> + /* VIRTIO Shared Memory Region ID */
> + uint8_t shmid;
> + uint8_t padding[7];
> + /* File offset */
> + uint64_t fd_offset;
> + /* Offset within the VIRTIO Shared Memory Region */
> + uint64_t shm_offset;
> + /* Size of the mapping */
> + uint64_t len;
> + /* Flags for the mmap operation, from VHOST_USER_FLAG_* */
> + uint64_t flags;
> +} VhostUserMMap;
> +
> typedef struct {
> VhostUserRequest request;
>
> @@ -224,6 +244,7 @@ typedef union {
> VhostUserInflight inflight;
> VhostUserShared object;
> VhostUserTransferDeviceState transfer_state;
> + VhostUserMMap mmap;
> } VhostUserPayload;
>
> typedef struct VhostUserMsg {
> @@ -1770,6 +1791,111 @@ vhost_user_backend_handle_shared_object_lookup(struct
> vhost_user *u,
> return 0;
> }
>
> +static int
> +vhost_user_backend_handle_shmem_map(struct vhost_dev *dev,
> + QIOChannel *ioc,
> + VhostUserHeader *hdr,
> + VhostUserPayload *payload,
> + int fd, Error **errp)
> +{
> + VirtSharedMemory *shmem = NULL;
> + VhostUserMMap *vu_mmap = &payload->mmap;
> + g_autoptr(GString) shm_name = g_string_new(NULL);
> +
> + if (fd < 0) {
> + error_report("Bad fd for map");
> + return -EBADF;
> + }
> +
> + if (!dev->vdev->shmem_list ||
> + dev->vdev->n_shmem_regions <= vu_mmap->shmid) {
> + error_report("Device only has %d VIRTIO Shared Memory Regions. "
> + "Requested ID: %d",
> + dev->vdev->n_shmem_regions, vu_mmap->shmid);
> + return -EFAULT;
> + }
> +
> + shmem = &dev->vdev->shmem_list[vu_mmap->shmid];
> +
> + if (!shmem) {
> + error_report("VIRTIO Shared Memory Region at "
> + "ID %d unitialized", vu_mmap->shmid);
> + return -EFAULT;
> + }
> +
> + if ((vu_mmap->shm_offset + vu_mmap->len) < vu_mmap->len ||
> + (vu_mmap->shm_offset + vu_mmap->len) > shmem->mr->size) {
> + error_report("Bad offset/len for mmap %" PRIx64 "+%" PRIx64,
> + vu_mmap->shm_offset, vu_mmap->len);
> + return -EFAULT;
> + }
> +
> + g_string_printf(shm_name, "virtio-shm%i-%lu",
> + vu_mmap->shmid, vu_mmap->shm_offset);
> +
> + memory_region_transaction_begin();
> + virtio_add_shmem_map(shmem, shm_name->str, vu_mmap->shm_offset,
> + vu_mmap->fd_offset, vu_mmap->len, fd, errp);
Error handling is missing. In particular, if virtio_add_shmem_map() sets
errp due to an error, then vhost_user_send_resp() will crash if it also
needs to set the error. An Error object can only be filled in once.
> +
> + hdr->size = sizeof(payload->u64);
> + vhost_user_send_resp(ioc, hdr, payload, errp);
payload->u64 has not been initialized. It contains the contents of
payload->mmap, which is not the u64 return value that must be sent here.
I think something like the following is necessary:
payload->u64 = 0;
> + memory_region_transaction_commit();
> +
> + return 0;
> +}
> +
> +static int
> +vhost_user_backend_handle_shmem_unmap(struct vhost_dev *dev,
> + QIOChannel *ioc,
> + VhostUserHeader *hdr,
> + VhostUserPayload *payload,
> + Error **errp)
> +{
> + VirtSharedMemory *shmem = NULL;
> + MappedMemoryRegion *mmap = NULL;
> + VhostUserMMap *vu_mmap = &payload->mmap;
> +
> + if (!dev->vdev->shmem_list ||
> + dev->vdev->n_shmem_regions <= vu_mmap->shmid) {
> + error_report("Device only has %d VIRTIO Shared Memory Regions. "
> + "Requested ID: %d",
> + dev->vdev->n_shmem_regions, vu_mmap->shmid);
> + return -EFAULT;
> + }
> +
> + shmem = &dev->vdev->shmem_list[vu_mmap->shmid];
> +
> + if (!shmem) {
> + error_report("VIRTIO Shared Memory Region at "
> + "ID %d unitialized", vu_mmap->shmid);
> + return -EFAULT;
> + }
> +
> + if ((vu_mmap->shm_offset + vu_mmap->len) < vu_mmap->len ||
> + (vu_mmap->shm_offset + vu_mmap->len) > shmem->mr->size) {
> + error_report("Bad offset/len for unmmap %" PRIx64 "+%" PRIx64,
> + vu_mmap->shm_offset, vu_mmap->len);
> + return -EFAULT;
> + }
> +
> + mmap = virtio_find_shmem_map(shmem, vu_mmap->shm_offset, vu_mmap->len);
> + if (!mmap) {
> + return -EFAULT;
> + }
> +
> + memory_region_transaction_begin();
> + memory_region_del_subregion(shmem->mr, mmap->mem);
> +
> + hdr->size = sizeof(payload->u64);
> + vhost_user_send_resp(ioc, hdr, payload, errp);
Same uninitialized payload->u64 issue here.
> + memory_region_transaction_commit();
> +
> + /* Free the MemoryRegion only after vhost_commit */
> + virtio_del_shmem_map(shmem, vu_mmap->shm_offset, vu_mmap->len);
> +
> + return 0;
> +}
> +
> static void close_backend_channel(struct vhost_user *u)
> {
> g_source_destroy(u->backend_src);
> @@ -1837,6 +1963,14 @@ static gboolean backend_read(QIOChannel *ioc,
> GIOCondition condition,
> case VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP:
> ret = vhost_user_backend_handle_shared_object_lookup(dev->opaque,
> ioc,
> &hdr, &payload);
> + case VHOST_USER_BACKEND_SHMEM_MAP:
> + ret = vhost_user_backend_handle_shmem_map(dev, ioc, &hdr, &payload,
> + fd ? fd[0] : -1,
> &local_err);
> + break;
> + case VHOST_USER_BACKEND_SHMEM_UNMAP:
> + ret = vhost_user_backend_handle_shmem_unmap(dev, ioc, &hdr, &payload,
> + &local_err);
> + break;
> break;
> default:
> error_report("Received unexpected msg type: %d.", hdr.request);
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 85110bce37..47d0ddb820 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -3063,6 +3063,75 @@ int virtio_save(VirtIODevice *vdev, QEMUFile *f)
> return vmstate_save_state(f, &vmstate_virtio, vdev, NULL);
> }
>
> +VirtSharedMemory *virtio_new_shmem_region(VirtIODevice *vdev)
> +{
> + ++vdev->n_shmem_regions;
> + vdev->shmem_list = g_renew(VirtSharedMemory, vdev->shmem_list,
> + vdev->n_shmem_regions);
> + vdev->shmem_list[vdev->n_shmem_regions - 1].mr = g_new0(MemoryRegion, 1);
> + QTAILQ_INIT(&vdev->shmem_list[vdev->n_shmem_regions - 1].mmaps);
QTAILQ cannot be used inside a struct that is reallocated using
g_renew() because a dangling tql_prev pointer will be left after
reallocation. From QTAILQ_INIT():
(head)->tqh_circ.tql_prev = &(head)->tqh_circ; <--- not realloc-safe
Instead of using g_renew() on an array, consider using a list from
"qemu/queue.h". Lookup by shmid becomes O(n) instead of O(1), but it
doesn't matter in practice since existing devices have a small number of
VIRTIO Shared Memory Regions.
> + return &vdev->shmem_list[vdev->n_shmem_regions - 1];
> +}
> +
> +void virtio_add_shmem_map(VirtSharedMemory *shmem, const char *shm_name,
> + hwaddr shm_offset, hwaddr fd_offset, uint64_t size,
> + int fd, Error **errp)
> +{
> + MappedMemoryRegion *mmap;
> + fd = dup(fd);
> + if (fd < 0) {
> + error_setg_errno(errp, errno, "Failed to duplicate fd");
> + return;
> + }
> +
> + if (shm_offset + size > shmem->mr->size) {
> + error_setg(errp, "Memory exceeds the shared memory boundaries");
> + return;
fd is leaked here.
> + }
> +
> + mmap = g_new0(MappedMemoryRegion, 1);
> + mmap->mem = g_new0(MemoryRegion, 1);
> + mmap->offset = shm_offset;
> + if (!memory_region_init_ram_from_fd(mmap->mem,
> + OBJECT(shmem->mr),
> + shm_name, size, RAM_SHARED,
> + fd, fd_offset, errp)) {
> + error_setg(errp, "Failed to mmap region %s", shm_name);
> + close(fd);
> + g_free(mmap->mem);
> + g_free(mmap);
> + return;
> + }
> + memory_region_add_subregion(shmem->mr, shm_offset, mmap->mem);
> +
> + QTAILQ_INSERT_TAIL(&shmem->mmaps, mmap, link);
> +}
> +
> +MappedMemoryRegion *virtio_find_shmem_map(VirtSharedMemory *shmem,
> + hwaddr offset, uint64_t size)
> +{
> + MappedMemoryRegion *mmap;
> + QTAILQ_FOREACH(mmap, &shmem->mmaps, link) {
> + if (mmap->offset == offset && mmap->mem->size == size) {
> + return mmap;
> + }
> + }
> + return NULL;
> +}
> +
> +void virtio_del_shmem_map(VirtSharedMemory *shmem, hwaddr offset,
> + uint64_t size)
> +{
> + MappedMemoryRegion *mmap = virtio_find_shmem_map(shmem, offset, size);
> + if (mmap == NULL) {
> + return;
> + }
> +
> + object_unparent(OBJECT(mmap->mem));
> + QTAILQ_REMOVE(&shmem->mmaps, mmap, link);
> + g_free(mmap);
> +}
> +
> /* A wrapper for use as a VMState .put function */
> static int virtio_device_put(QEMUFile *f, void *opaque, size_t size,
> const VMStateField *field, JSONWriter *vmdesc)
> @@ -3492,6 +3561,8 @@ void virtio_init(VirtIODevice *vdev, uint16_t
> device_id, size_t config_size)
> virtio_vmstate_change, vdev);
> vdev->device_endian = virtio_default_endian();
> vdev->use_guest_notifier_mask = true;
> + vdev->shmem_list = NULL;
> + vdev->n_shmem_regions = 0;
> }
>
> /*
> @@ -4005,11 +4076,21 @@ static void
> virtio_device_free_virtqueues(VirtIODevice *vdev)
> static void virtio_device_instance_finalize(Object *obj)
> {
> VirtIODevice *vdev = VIRTIO_DEVICE(obj);
> + VirtSharedMemory *shmem = NULL;
> + int i;
>
> virtio_device_free_virtqueues(vdev);
>
> g_free(vdev->config);
> g_free(vdev->vector_queues);
> + for (i = 0; i< vdev->n_shmem_regions; i++) {
> + shmem = &vdev->shmem_list[i];
> + while (!QTAILQ_EMPTY(&shmem->mmaps)) {
> + MappedMemoryRegion *mmap_reg = QTAILQ_FIRST(&shmem->mmaps);
> + QTAILQ_REMOVE(&shmem->mmaps, mmap_reg, link);
> + g_free(mmap_reg);
Is it possible to reuse virtio_del_shmem_map() to avoid code duplication
and inconsistencies?
while (!QTAILQ_EMPTY(&shmem->mmaps)) {
MappedMemoryRegion *mmap_reg = QTAILQ_FIRST(&shmem->mmaps);
virtio_del_shmem_map(shmem, mmap_reg->offset, mmap_reg->mem->size);
}
> + }
> + }
Missing g_free(vdev->shmem_list).
> }
>
> static const Property virtio_properties[] = {
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 6386910280..a778547c79 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -98,6 +98,21 @@ enum virtio_device_endian {
> VIRTIO_DEVICE_ENDIAN_BIG,
> };
>
> +struct MappedMemoryRegion {
> + MemoryRegion *mem;
> + hwaddr offset;
> + QTAILQ_ENTRY(MappedMemoryRegion) link;
> +};
> +
> +typedef struct MappedMemoryRegion MappedMemoryRegion;
> +
> +struct VirtSharedMemory {
> + MemoryRegion *mr;
> + QTAILQ_HEAD(, MappedMemoryRegion) mmaps;
> +};
> +
> +typedef struct VirtSharedMemory VirtSharedMemory;
> +
> /**
> * struct VirtIODevice - common VirtIO structure
> * @name: name of the device
> @@ -167,6 +182,9 @@ struct VirtIODevice
> */
> EventNotifier config_notifier;
> bool device_iotlb_enabled;
> + /* Shared memory region for vhost-user mappings. */
This is core VIRTIO code and Shared Memory Regions are a VIRTIO concept.
It is possible that built-in (non-vhost) devices might also add their
shared memory regions with virtio_new_shmem_region(), so let's not talk
about vhost-user specifically.
> + VirtSharedMemory *shmem_list;
> + int n_shmem_regions;
> };
>
> struct VirtioDeviceClass {
> @@ -289,6 +307,15 @@ void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);
>
> int virtio_save(VirtIODevice *vdev, QEMUFile *f);
>
> +VirtSharedMemory *virtio_new_shmem_region(VirtIODevice *vdev);
> +void virtio_add_shmem_map(VirtSharedMemory *shmem, const char *shm_name,
> + hwaddr shm_offset, hwaddr fd_offset, uint64_t size,
> + int fd, Error **errp);
> +MappedMemoryRegion *virtio_find_shmem_map(VirtSharedMemory *shmem, hwaddr
> offset,
> + uint64_t size);
> +void virtio_del_shmem_map(VirtSharedMemory *shmem, hwaddr offset,
> + uint64_t size);
> +
> extern const VMStateInfo virtio_vmstate_info;
>
> #define VMSTATE_VIRTIO_DEVICE \
> diff --git a/subprojects/libvhost-user/libvhost-user.c
> b/subprojects/libvhost-user/libvhost-user.c
> index 9c630c2170..034cbfdc3c 100644
> --- a/subprojects/libvhost-user/libvhost-user.c
> +++ b/subprojects/libvhost-user/libvhost-user.c
> @@ -1592,6 +1592,76 @@ vu_rm_shared_object(VuDev *dev, unsigned char
> uuid[UUID_LEN])
> return vu_send_message(dev, &msg);
> }
>
> +bool
> +vu_shmem_map(VuDev *dev, uint8_t shmid, uint64_t fd_offset,
> + uint64_t shm_offset, uint64_t len, uint64_t flags, int fd)
> +{
> + VhostUserMsg vmsg = {
> + .request = VHOST_USER_BACKEND_SHMEM_MAP,
> + .size = sizeof(vmsg.payload.mmap),
> + .flags = VHOST_USER_VERSION,
> + .payload.mmap = {
> + .shmid = shmid,
> + .fd_offset = fd_offset,
> + .shm_offset = shm_offset,
> + .len = len,
> + .flags = flags,
> + },
> + .fd_num = 1,
> + .fds[0] = fd,
> + };
> +
> + if (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SHMEM)) {
> + return false;
> + }
> +
> + if (vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_REPLY_ACK)) {
> + vmsg.flags |= VHOST_USER_NEED_REPLY_MASK;
> + }
Setting this flag is inconsistent with
vhost_user_backend_handle_shmem_map() and
vhost_user_backend_handle_shmem_unmap(). They call
vhost_user_send_resp() explicitly instead of relying on backend_read()
to send the return value when VHOST_USER_NEED_REPLY_MASK is set. This
inconsistency means that a successful return message will be sent twice
when VHOST_USER_NEED_REPLY_MASK is set.
Either these new vhost-user messages could be specified with a mandatory
reply payload or the patch could be updated to avoid the explicit
vhost_user_send_resp() calls. I think the latter is more commonly used
by other vhost-user messages, so it's probably best to do it the same
way.
> +
> + pthread_mutex_lock(&dev->backend_mutex);
> + if (!vu_message_write(dev, dev->backend_fd, &vmsg)) {
> + pthread_mutex_unlock(&dev->backend_mutex);
> + return false;
> + }
> +
> + /* Also unlocks the backend_mutex */
> + return vu_process_message_reply(dev, &vmsg);
> +}
> +
> +bool
> +vu_shmem_unmap(VuDev *dev, uint8_t shmid, uint64_t shm_offset, uint64_t len)
> +{
> + VhostUserMsg vmsg = {
> + .request = VHOST_USER_BACKEND_SHMEM_UNMAP,
> + .size = sizeof(vmsg.payload.mmap),
> + .flags = VHOST_USER_VERSION,
> + .payload.mmap = {
> + .shmid = shmid,
> + .fd_offset = 0,
> + .shm_offset = shm_offset,
> + .len = len,
> + },
> + };
> +
> + if (!vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_SHMEM)) {
> + return false;
> + }
> +
> + if (vu_has_protocol_feature(dev, VHOST_USER_PROTOCOL_F_REPLY_ACK)) {
> + vmsg.flags |= VHOST_USER_NEED_REPLY_MASK;
> + }
> +
> + pthread_mutex_lock(&dev->backend_mutex);
> + if (!vu_message_write(dev, dev->backend_fd, &vmsg)) {
> + pthread_mutex_unlock(&dev->backend_mutex);
> + return false;
> + }
> +
> + /* Also unlocks the backend_mutex */
> + return vu_process_message_reply(dev, &vmsg);
> +}
> +
> static bool
> vu_set_vring_call_exec(VuDev *dev, VhostUserMsg *vmsg)
> {
> diff --git a/subprojects/libvhost-user/libvhost-user.h
> b/subprojects/libvhost-user/libvhost-user.h
> index 2ffc58c11b..e9adb836f0 100644
> --- a/subprojects/libvhost-user/libvhost-user.h
> +++ b/subprojects/libvhost-user/libvhost-user.h
> @@ -69,6 +69,8 @@ enum VhostUserProtocolFeature {
> /* Feature 16 is reserved for VHOST_USER_PROTOCOL_F_STATUS. */
> /* Feature 17 reserved for VHOST_USER_PROTOCOL_F_XEN_MMAP. */
> VHOST_USER_PROTOCOL_F_SHARED_OBJECT = 18,
> + /* Feature 19 is reserved for VHOST_USER_PROTOCOL_F_DEVICE_STATE */
> + VHOST_USER_PROTOCOL_F_SHMEM = 20,
> VHOST_USER_PROTOCOL_F_MAX
> };
>
> @@ -127,6 +129,8 @@ typedef enum VhostUserBackendRequest {
> VHOST_USER_BACKEND_SHARED_OBJECT_ADD = 6,
> VHOST_USER_BACKEND_SHARED_OBJECT_REMOVE = 7,
> VHOST_USER_BACKEND_SHARED_OBJECT_LOOKUP = 8,
> + VHOST_USER_BACKEND_SHMEM_MAP = 9,
> + VHOST_USER_BACKEND_SHMEM_UNMAP = 10,
> VHOST_USER_BACKEND_MAX
> } VhostUserBackendRequest;
>
> @@ -186,6 +190,24 @@ typedef struct VhostUserShared {
> unsigned char uuid[UUID_LEN];
> } VhostUserShared;
>
> +/* For the flags field of VhostUserMMap */
> +#define VHOST_USER_FLAG_MAP_R (1u << 0)
> +#define VHOST_USER_FLAG_MAP_W (1u << 1)
> +
> +typedef struct {
> + /* VIRTIO Shared Memory Region ID */
> + uint8_t shmid;
> + uint8_t padding[7];
> + /* File offset */
> + uint64_t fd_offset;
> + /* Offset within the VIRTIO Shared Memory Region */
> + uint64_t shm_offset;
> + /* Size of the mapping */
> + uint64_t len;
> + /* Flags for the mmap operation, from VHOST_USER_FLAG_* */
> + uint64_t flags;
> +} VhostUserMMap;
> +
> #define VU_PACKED __attribute__((packed))
>
> typedef struct VhostUserMsg {
> @@ -210,6 +232,7 @@ typedef struct VhostUserMsg {
> VhostUserVringArea area;
> VhostUserInflight inflight;
> VhostUserShared object;
> + VhostUserMMap mmap;
> } payload;
>
> int fds[VHOST_MEMORY_BASELINE_NREGIONS];
> @@ -593,6 +616,38 @@ bool vu_add_shared_object(VuDev *dev, unsigned char
> uuid[UUID_LEN]);
> */
> bool vu_rm_shared_object(VuDev *dev, unsigned char uuid[UUID_LEN]);
>
> +/**
> + * vu_shmem_map:
> + * @dev: a VuDev context
> + * @shmid: VIRTIO Shared Memory Region ID
> + * @fd_offset: File offset
> + * @shm_offset: Offset within the VIRTIO Shared Memory Region
> + * @len: Size of the mapping
> + * @flags: Flags for the mmap operation
> + * @fd: A file descriptor
> + *
> + * Advertises a new mapping to be made in a given VIRTIO Shared Memory
> Region.
> + *
> + * Returns: TRUE on success, FALSE on failure.
> + */
> +bool vu_shmem_map(VuDev *dev, uint8_t shmid, uint64_t fd_offset,
> + uint64_t shm_offset, uint64_t len, uint64_t flags, int fd);
> +
> +/**
> + * vu_shmem_unmap:
> + * @dev: a VuDev context
> + * @shmid: VIRTIO Shared Memory Region ID
> + * @fd_offset: File offset
> + * @len: Size of the mapping
> + *
> + * The front-end un-mmaps a given range in the VIRTIO Shared Memory Region
> + * with the requested `shmid`.
> + *
> + * Returns: TRUE on success, FALSE on failure.
> + */
> +bool vu_shmem_unmap(VuDev *dev, uint8_t shmid, uint64_t shm_offset,
> + uint64_t len);
> +
> /**
> * vu_queue_set_notification:
> * @dev: a VuDev context
> --
> 2.48.1
>
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