linux/arch/um/drivers/ubd_user.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2016 Anton Ivanov (aivanov@brocade.com)
 * Copyright (C) 2000, 2001, 2002 Jeff Dike (jdike@karaya.com)
 * Copyright (C) 2001 Ridgerun,Inc (glonnon@ridgerun.com)
 */

#include <stddef.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>
#include <signal.h>
#include <string.h>
#include <netinet/in.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <endian.h>
#include <byteswap.h>

#include "ubd.h"
#include <os.h>
#include <poll.h>

struct pollfd kernel_pollfd;

int start_io_thread(unsigned long sp, int *fd_out)
{
	int pid, fds[2], err;

	err = os_pipe(fds, 1, 1);
	if(err < 0){
		printk("start_io_thread - os_pipe failed, err = %d\n", -err);
		goto out;
	}

	kernel_fd = fds[0];
	kernel_pollfd.fd = kernel_fd;
	kernel_pollfd.events = POLLIN;
	*fd_out = fds[1];

	err = os_set_fd_block(*fd_out, 0);
	err = os_set_fd_block(kernel_fd, 0);
	if (err) {
		printk("start_io_thread - failed to set nonblocking I/O.\n");
		goto out_close;
	}

	pid = clone(io_thread, (void *) sp, CLONE_FILES | CLONE_VM, NULL);
	if(pid < 0){
		err = -errno;
		printk("start_io_thread - clone failed : errno = %d\n", errno);
		goto out_close;
	}

	return(pid);

 out_close:
	os_close_file(fds[0]);
	os_close_file(fds[1]);
	kernel_fd = -1;
	*fd_out = -1;
 out:
	return err;
}

int ubd_read_poll(int timeout)
{
	kernel_pollfd.events = POLLIN;
	return poll(&kernel_pollfd, 1, timeout);
}
int ubd_write_poll(int timeout)
{
	kernel_pollfd.events = POLLOUT;
	return poll(&kernel_pollfd, 1, timeout);
}