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vhost-user: add slave-req-fd support
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Learn to give a socket to the slave to let him make requests to the
master.

Signed-off-by: Marc-André Lureau <[email protected]>
Signed-off-by: Maxime Coquelin <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>
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@elmarco @lacraig2
elmarco authored and lacraig2 committed Jan 22, 2024
1 parent 7a220d7 commit 1f337c1
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Showing 2 changed files with 158 additions and 8 deletions.
32 changes: 30 additions & 2 deletions docs/specs/vhost-user.txt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -139,6 +139,7 @@ in the ancillary data:
* VHOST_USER_SET_VRING_KICK
* VHOST_USER_SET_VRING_CALL
* VHOST_USER_SET_VRING_ERR
* VHOST_USER_SET_SLAVE_REQ_FD

If Master is unable to send the full message or receives a wrong reply it will
close the connection. An optional reconnection mechanism can be implemented.
Expand Down Expand Up @@ -252,6 +253,18 @@ Once the source has finished migration, rings will be stopped by
the source. No further update must be done before rings are
restarted.

Slave communication
-------------------

An optional communication channel is provided if the slave declares
VHOST_USER_PROTOCOL_F_SLAVE_REQ protocol feature, to allow the slave to make
requests to the master.

The fd is provided via VHOST_USER_SET_SLAVE_REQ_FD ancillary data.

A slave may then send VHOST_USER_SLAVE_* messages to the master
using this fd communication channel.

Protocol features
-----------------

Expand All @@ -260,9 +273,10 @@ Protocol features
#define VHOST_USER_PROTOCOL_F_RARP 2
#define VHOST_USER_PROTOCOL_F_REPLY_ACK 3
#define VHOST_USER_PROTOCOL_F_MTU 4
#define VHOST_USER_PROTOCOL_F_SLAVE_REQ 5

Message types
-------------
Master message types
--------------------

* VHOST_USER_GET_FEATURES

Expand Down Expand Up @@ -486,6 +500,20 @@ Message types
If VHOST_USER_PROTOCOL_F_REPLY_ACK is negotiated, slave must respond
with zero in case the specified MTU is valid, or non-zero otherwise.

* VHOST_USER_SET_SLAVE_REQ_FD

Id: 21
Equivalent ioctl: N/A
Master payload: N/A

Set the socket file descriptor for slave initiated requests. It is passed
in the ancillary data.
This request should be sent only when VHOST_USER_F_PROTOCOL_FEATURES
has been negotiated, and protocol feature bit VHOST_USER_PROTOCOL_F_SLAVE_REQ
bit is present in VHOST_USER_GET_PROTOCOL_FEATURES.
If VHOST_USER_PROTOCOL_F_REPLY_ACK is negotiated, slave must respond
with zero for success, non-zero otherwise.

VHOST_USER_PROTOCOL_F_REPLY_ACK:
-------------------------------
The original vhost-user specification only demands replies for certain
Expand Down
134 changes: 128 additions & 6 deletions hw/virtio/vhost-user.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@ enum VhostUserProtocolFeature {
VHOST_USER_PROTOCOL_F_RARP = 2,
VHOST_USER_PROTOCOL_F_REPLY_ACK = 3,
VHOST_USER_PROTOCOL_F_NET_MTU = 4,
VHOST_USER_PROTOCOL_F_SLAVE_REQ = 5,

VHOST_USER_PROTOCOL_F_MAX
};
Expand Down Expand Up @@ -61,9 +62,15 @@ typedef enum VhostUserRequest {
VHOST_USER_SET_VRING_ENABLE = 18,
VHOST_USER_SEND_RARP = 19,
VHOST_USER_NET_SET_MTU = 20,
VHOST_USER_SET_SLAVE_REQ_FD = 21,
VHOST_USER_MAX
} VhostUserRequest;

typedef enum VhostUserSlaveRequest {
VHOST_USER_SLAVE_NONE = 0,
VHOST_USER_SLAVE_MAX
} VhostUserSlaveRequest;

typedef struct VhostUserMemoryRegion {
uint64_t guest_phys_addr;
uint64_t memory_size;
Expand Down Expand Up @@ -111,6 +118,11 @@ static VhostUserMsg m __attribute__ ((unused));
/* The version of the protocol we support */
#define VHOST_USER_VERSION (0x1)

struct vhost_user {
CharBackend *chr;
int slave_fd;
};

static bool ioeventfd_enabled(void)
{
return kvm_enabled() && kvm_eventfds_enabled();
Expand Down Expand Up @@ -573,16 +585,110 @@ static int vhost_user_reset_device(struct vhost_dev *dev)
return 0;
}

static int vhost_user_slave_handle_config_change(struct vhost_dev *dev)
static void slave_read(void *opaque)
{
int ret = -1;
struct vhost_dev *dev = opaque;
struct vhost_user *u = dev->opaque;
VhostUserMsg msg = { 0, };
int size, ret = 0;

/* Read header */
size = read(u->slave_fd, &msg, VHOST_USER_HDR_SIZE);
if (size != VHOST_USER_HDR_SIZE) {
error_report("Failed to read from slave.");
goto err;
}

if (msg.size > VHOST_USER_PAYLOAD_SIZE) {
error_report("Failed to read msg header."
" Size %d exceeds the maximum %zu.", msg.size,
VHOST_USER_PAYLOAD_SIZE);
goto err;
}

/* Read payload */
size = read(u->slave_fd, &msg.payload, msg.size);
if (size != msg.size) {
error_report("Failed to read payload from slave.");
goto err;
}

switch (msg.request) {
default:
error_report("Received unexpected msg type.");
ret = -EINVAL;
}

/*
* REPLY_ACK feature handling. Other reply types has to be managed
* directly in their request handlers.
*/
if (msg.flags & VHOST_USER_NEED_REPLY_MASK) {
msg.flags &= ~VHOST_USER_NEED_REPLY_MASK;
msg.flags |= VHOST_USER_REPLY_MASK;

if (!dev->config_ops) {
msg.payload.u64 = !!ret;
msg.size = sizeof(msg.payload.u64);

size = write(u->slave_fd, &msg, VHOST_USER_HDR_SIZE + msg.size);
if (size != VHOST_USER_HDR_SIZE + msg.size) {
error_report("Failed to send msg reply to slave.");
goto err;
}
}

return;

err:
qemu_set_fd_handler(u->slave_fd, NULL, NULL, NULL);
close(u->slave_fd);
u->slave_fd = -1;
return;
}

static int vhost_setup_slave_channel(struct vhost_dev *dev)
{
VhostUserMsg msg = {
.request = VHOST_USER_SET_SLAVE_REQ_FD,
.flags = VHOST_USER_VERSION,
};
struct vhost_user *u = dev->opaque;
int sv[2], ret = 0;
bool reply_supported = virtio_has_feature(dev->protocol_features,
VHOST_USER_PROTOCOL_F_REPLY_ACK);

if (!virtio_has_feature(dev->protocol_features,
VHOST_USER_PROTOCOL_F_SLAVE_REQ)) {
return 0;
}

if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
error_report("socketpair() failed");
return -1;
}

if (dev->config_ops->vhost_dev_config_notifier) {
ret = dev->config_ops->vhost_dev_config_notifier(dev);
u->slave_fd = sv[0];
qemu_set_fd_handler(u->slave_fd, slave_read, NULL, dev);

if (reply_supported) {
msg.flags |= VHOST_USER_NEED_REPLY_MASK;
}

ret = vhost_user_write(dev, &msg, &sv[1], 1);
if (ret) {
goto out;
}

if (reply_supported) {
ret = process_message_reply(dev, &msg);
}

out:
close(sv[1]);
if (ret) {
qemu_set_fd_handler(u->slave_fd, NULL, NULL, NULL);
close(u->slave_fd);
u->slave_fd = -1;
}

return ret;
Expand All @@ -595,7 +701,10 @@ static int vhost_user_init(struct vhost_dev *dev, void *opaque)

assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);

dev->opaque = opaque;
u = g_new0(struct vhost_user, 1);
u->chr = opaque;
u->slave_fd = -1;
dev->opaque = u;

err = vhost_user_get_features(dev, &features);
if (err < 0) {
Expand Down Expand Up @@ -635,13 +744,26 @@ static int vhost_user_init(struct vhost_dev *dev, void *opaque)
"VHOST_USER_PROTOCOL_F_LOG_SHMFD feature.");
}

err = vhost_setup_slave_channel(dev);
if (err < 0) {
return err;
}

return 0;
}

static int vhost_user_cleanup(struct vhost_dev *dev)
{
struct vhost_user *u;

assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);

u = dev->opaque;
if (u->slave_fd >= 0) {
close(u->slave_fd);
u->slave_fd = -1;
}
g_free(u);
dev->opaque = 0;

return 0;
Expand Down

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