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seat: preserve current VT on transient update failures and fix errno semantics for free-VT lookup #4

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seat: preserve current VT on transient update failures and fix errno semantics for free-VT lookup #4

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8244959
Initial plan
Copilot Jun 2, 2026
fb71d1f
feat(control): expose VT management over DDE control socket
Jun 2, 2026
ef50dcd
fix(seat): keep cur_vt stable on VT query errors
Copilot Jun 2, 2026
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14 changes: 14 additions & 0 deletions include/control.h
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Original file line number Diff line number Diff line change
Expand Up @@ -18,8 +18,14 @@ struct server;
enum control_opcode {
CONTROL_CREATE_GROUP_VT = 1,
CONTROL_DESTROY_GROUP_VT = 2,
CONTROL_GET_ACTIVE_VT = 3,
CONTROL_FIND_FREE_VT = 4,
CONTROL_SWITCH_VT = 5,
CONTROL_GROUP_VT_CREATED = 100,
CONTROL_VT_CHANGED = 101,
CONTROL_OK = 102,
CONTROL_ACTIVE_VT = 103,
CONTROL_FREE_VT = 104,
CONTROL_ERROR = 255,
};

Expand All @@ -39,11 +45,19 @@ struct control_destroy_group_vt_request {
int32_t vt;
};

struct control_switch_vt_request {
int32_t vt;
};

struct control_group_vt_created_event {
int32_t owner_pid;
int32_t vt;
};

struct control_vt_state_event {
int32_t vt;
};

struct control_vt_change_event {
int32_t old_vt;
int32_t new_vt;
Expand Down
3 changes: 3 additions & 0 deletions include/seat.h
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,9 @@ struct seat_device *seat_find_device(struct client *client, int device_id);
int seat_set_next_session(struct client *client, int session);
int seat_vt_activate(struct seat *seat);
int seat_vt_release(struct seat *seat);
int seat_get_active_vt(struct seat *seat);
int seat_find_available_vt(struct seat *seat);
int seat_switch_vt(struct seat *seat, int vt);
int seat_create_group_vt(struct seat *seat, struct client *owner, int requested_vt,
const char *user, const char *session);
int seat_destroy_group_vt(struct seat *seat, int vt);
Expand Down
76 changes: 76 additions & 0 deletions seatd/control.c
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Original file line number Diff line number Diff line change
Expand Up @@ -129,6 +129,17 @@ static int control_send_error(struct control_client *client, int error_code) {
return control_client_flush(client);
}

static int control_send_ok(struct control_client *client) {
struct control_header header = {
.opcode = CONTROL_OK,
.size = 0,
};
if (connection_put(&client->connection, &header, sizeof(header)) == -1) {
return -1;
}
return control_client_flush(client);
}

static int control_send_message(struct control_client *client, uint16_t opcode,
const void *payload, uint16_t payload_size) {
struct control_header header = {
Expand All @@ -150,6 +161,13 @@ static int control_send_group_vt_created(struct control_client *client, pid_t ow
return control_send_message(client, CONTROL_GROUP_VT_CREATED, &event, sizeof(event));
}

static int control_send_vt_state(struct control_client *client, uint16_t opcode, int vt) {
struct control_vt_state_event event = {
.vt = vt,
};
return control_send_message(client, opcode, &event, sizeof(event));
}

static int control_send_vt_change(struct control_client *client, int old_vt, int new_vt) {
struct control_vt_change_event event = {
.old_vt = old_vt,
Expand Down Expand Up @@ -221,6 +239,49 @@ static int handle_destroy_group_vt(struct control_client *client) {
return 0;
}

static int handle_get_active_vt(struct control_client *client) {
struct seat *seat = server_get_seat(client->server, "seat0");
if (seat == NULL) {
return control_send_error(client, ENOENT);
}

int vt = seat_get_active_vt(seat);
if (vt == -1) {
return control_send_error(client, errno);
}
return control_send_vt_state(client, CONTROL_ACTIVE_VT, vt);
}

static int handle_find_free_vt(struct control_client *client) {
struct seat *seat = server_get_seat(client->server, "seat0");
if (seat == NULL) {
return control_send_error(client, ENOENT);
}

int vt = seat_find_available_vt(seat);
if (vt == -1) {
return control_send_error(client, errno);
}
return control_send_vt_state(client, CONTROL_FREE_VT, vt);
}

static int handle_switch_vt(struct control_client *client) {
struct control_switch_vt_request request;
if (connection_get(&client->connection, &request, sizeof(request)) == -1) {
return 0;
}

struct seat *seat = server_get_seat(client->server, "seat0");
if (seat == NULL) {
return control_send_error(client, ENOENT);
}

if (seat_switch_vt(seat, request.vt) == -1) {
return control_send_error(client, errno);
}
return control_send_ok(client);
}

static int control_client_handle_opcode(struct control_client *client, uint16_t opcode,
uint16_t size) {
switch (opcode) {
Expand All @@ -234,6 +295,21 @@ static int control_client_handle_opcode(struct control_client *client, uint16_t
return control_send_error(client, EPROTO);
}
return handle_destroy_group_vt(client);
case CONTROL_GET_ACTIVE_VT:
if (size != 0) {
return control_send_error(client, EPROTO);
}
return handle_get_active_vt(client);
case CONTROL_FIND_FREE_VT:
if (size != 0) {
return control_send_error(client, EPROTO);
}
return handle_find_free_vt(client);
case CONTROL_SWITCH_VT:
if (size != sizeof(struct control_switch_vt_request)) {
return control_send_error(client, EPROTO);
}
return handle_switch_vt(client);
default:
return control_send_error(client, EPROTO);
}
Expand Down
95 changes: 89 additions & 6 deletions seatd/seat.c
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,7 @@ struct seat *seat_create(const char *seat_name, bool vt_bound) {
linked_list_init(&seat->group_vts);
seat->vt_bound = vt_bound;
seat->seat_name = strdup(seat_name);
seat->cur_vt = 0;
seat->cur_vt = -1;
if (seat->seat_name == NULL) {
free(seat);
return NULL;
Expand Down Expand Up @@ -74,14 +74,23 @@ void seat_destroy(struct seat *seat) {
free(seat);
}

static void seat_update_vt(struct seat *seat) {
static int seat_update_vt(struct seat *seat) {
int tty0fd = terminal_open(0);
if (tty0fd == -1) {
log_errorf("Could not open tty0 to update VT: %s", strerror(errno));
return;
return -1;
}
seat->cur_vt = terminal_current_vt(tty0fd);

int vt = terminal_current_vt(tty0fd);
int saved_errno = errno;
close(tty0fd);
if (vt <= 0) {
errno = saved_errno != 0 ? saved_errno : ENOENT;
return -1;
}

seat->cur_vt = vt;
return 0;
}

static int vt_open(int vt) {
Expand Down Expand Up @@ -117,8 +126,20 @@ static int vt_switch(struct seat *seat, int vt) {
log_errorf("Could not open terminal to switch to VT %d: %s", vt, strerror(errno));
return -1;
}
terminal_set_process_switching(ttyfd, true);
terminal_switch_vt(ttyfd, vt);

if (terminal_set_process_switching(ttyfd, true) == -1) {
int saved_errno = errno;
close(ttyfd);
errno = saved_errno;
return -1;
}
if (terminal_switch_vt(ttyfd, vt) == -1) {
int saved_errno = errno;
close(ttyfd);
errno = saved_errno;
return -1;
}

close(ttyfd);
return 0;
}
Expand Down Expand Up @@ -939,6 +960,68 @@ int seat_vt_release(struct seat *seat) {
return 0;
}

int seat_get_active_vt(struct seat *seat) {
if (!seat->vt_bound) {
errno = EINVAL;
return -1;
}

if (seat_update_vt(seat) == -1) {
return -1;
}
return seat->cur_vt;
}

int seat_find_available_vt(struct seat *seat) {
if (!seat->vt_bound) {
errno = EINVAL;
return -1;
}

int tty0fd = terminal_open(0);
if (tty0fd == -1) {
return -1;
}

int vt = terminal_find_available(tty0fd);
int saved_errno = errno;
close(tty0fd);
if (vt == -1) {
errno = saved_errno;
}
return vt;
}

int seat_switch_vt(struct seat *seat, int vt) {
if (!seat->vt_bound) {
errno = EINVAL;
return -1;
}
if (vt <= 0) {
errno = EINVAL;
return -1;
}

if (seat_update_vt(seat) == -1) {
return -1;
}
if (seat->cur_vt == vt) {
return 0;
}

if (seat->pending_vt_switch > 0) {
errno = EBUSY;
return -1;
}

seat->pending_vt_switch = vt;
if (vt_switch(seat, vt) == -1) {
seat->pending_vt_switch = 0;
return -1;
}
return 0;
}

int seat_create_group_vt(struct seat *seat, struct client *owner, int requested_vt,
const char *user, const char *session) {
if (!seat->vt_bound) {
Expand Down
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