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/*
* Copyright (C) 2026 Daniel Golle <daniel@makrotopia.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation
*
* This program 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 General Public License for more details.
*/
#ifndef __STDIO_FDS_H
#define __STDIO_FDS_H
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#define STDIO_FDS_NUM 3
#define FDS_NUM_MAX (STDIO_FDS_NUM + 1)
/*
* ubus carries a single file descriptor per request, so descriptor sets
* travel as SCM_RIGHTS over a socket pair whose receiving end is what gets
* passed to ubus_invoke_fd(). The payload byte carries the count.
*/
static inline int fds_send(const int *fds, int num)
{
char cmsgbuf[CMSG_SPACE(FDS_NUM_MAX * sizeof(int))];
struct msghdr msg = { 0 };
struct cmsghdr *cmsg;
struct iovec iov;
char count;
int sp[2];
if (num < 1 || num > FDS_NUM_MAX)
return -1;
if (socketpair(AF_UNIX, SOCK_STREAM, 0, sp))
return -1;
count = num;
iov.iov_base = &count;
iov.iov_len = sizeof(count);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = cmsgbuf;
msg.msg_controllen = CMSG_SPACE(num * sizeof(int));
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(num * sizeof(int));
memcpy(CMSG_DATA(cmsg), fds, num * sizeof(int));
if (sendmsg(sp[0], &msg, 0) < 0) {
close(sp[0]);
close(sp[1]);
return -1;
}
close(sp[0]);
return sp[1];
}
static inline int fds_recv(int sock, int *fds, int max)
{
char cmsgbuf[CMSG_SPACE(FDS_NUM_MAX * sizeof(int))];
int tmp[FDS_NUM_MAX];
struct msghdr msg = { 0 };
struct cmsghdr *cmsg;
struct iovec iov;
char count;
int num, i;
iov.iov_base = &count;
iov.iov_len = sizeof(count);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
msg.msg_control = cmsgbuf;
msg.msg_controllen = sizeof(cmsgbuf);
if (recvmsg(sock, &msg, MSG_CMSG_CLOEXEC | MSG_DONTWAIT) < 1)
return -1;
cmsg = CMSG_FIRSTHDR(&msg);
if (!cmsg || cmsg->cmsg_level != SOL_SOCKET ||
cmsg->cmsg_type != SCM_RIGHTS ||
cmsg->cmsg_len < CMSG_LEN(sizeof(int)) ||
cmsg->cmsg_len > CMSG_LEN(FDS_NUM_MAX * sizeof(int)))
return -1;
num = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
memcpy(tmp, CMSG_DATA(cmsg), num * sizeof(int));
if (num != count || num > max) {
for (i = 0; i < num; i++)
close(tmp[i]);
return -1;
}
memcpy(fds, tmp, num * sizeof(int));
return num;
}
static inline int stdio_notify_fds_send(const int *stdio_fds, int notify_fd)
{
int fds[FDS_NUM_MAX];
int num = 0;
if (stdio_fds) {
memcpy(fds, stdio_fds, STDIO_FDS_NUM * sizeof(int));
num = STDIO_FDS_NUM;
}
if (notify_fd > -1)
fds[num++] = notify_fd;
if (!num)
return -1;
return fds_send(fds, num);
}
static inline int stdio_notify_fds_recv(int sock, int *stdio_fds, int *notify_fd)
{
int fds[FDS_NUM_MAX];
int num;
num = fds_recv(sock, fds, FDS_NUM_MAX);
switch (num) {
case 1:
*notify_fd = fds[0];
return 0;
case STDIO_FDS_NUM + 1:
*notify_fd = fds[STDIO_FDS_NUM];
/* fallthrough */
case STDIO_FDS_NUM:
memcpy(stdio_fds, fds, STDIO_FDS_NUM * sizeof(int));
return 0;
default:
while (num > 0)
close(fds[--num]);
return -1;
}
}
static inline void stdio_fds_close(int *fds)
{
int i;
for (i = 0; i < STDIO_FDS_NUM; i++) {
if (fds[i] < 0)
continue;
close(fds[i]);
fds[i] = -1;
}
}
#endif
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