/*-
 * Copyright (c) 2011 Advanced Computing Technologies LLC
 * Written by: John H. Baldwin <jhb@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

/*
 * Simple driver to demonstrate the d_mmap_single() method as well as
 * the cdevpriv(9) API.  It provides a simple shared memory file
 * descriptor similar to shm_open() with SHM_ANON.
 */

#include <sys/param.h>
#include <sys/conf.h>
#include <sys/fcntl.h>
#include <sys/kernel.h>
#include <sys/module.h>
#include <sys/proc.h>
#include <sys/systm.h>
#include <vm/vm.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pager.h>

static d_open_t		memfd_open;
static d_mmap_single_t	memfd_mmap_single;
static void		memfd_dtor(void *);

static struct cdevsw memfd_cdevsw = {
	.d_version =	D_VERSION,
	.d_open =	memfd_open,
	.d_mmap_single = memfd_mmap_single,
	.d_name =	"memfd",
};

static int
memfd_open(struct cdev *cdev, int oflags, int devtype, struct thread *td)
{
	vm_object_t mem;
	int error;

	/* Read-only and write-only opens make no sense. */
	if ((oflags & (FREAD | FWRITE)) != (FREAD | FWRITE))
		return (EINVAL);

	/* Create a default VM object for each open file descriptor. */
	mem = vm_pager_allocate(OBJT_DEFAULT, NULL, 0, VM_PROT_DEFAULT, 0,
	    curthread->td_ucred);
	VM_OBJECT_LOCK(mem);
	vm_object_clear_flag(mem, OBJ_ONEMAPPING);
	vm_object_set_flag(mem, OBJ_NOSPLIT);
	VM_OBJECT_UNLOCK(mem);
	error = devfs_set_cdevpriv(mem, memfd_dtor);
	if (error != 0)
		vm_object_deallocate(mem);
	return (error);
}

static int
memfd_mmap_single(struct cdev *cdev, vm_ooffset_t *offset, vm_size_t size,
    vm_object_t *object, int nprot)
{
	vm_object_t mem;
	vm_pindex_t objsize;
	vm_ooffset_t delta;
	int error;

	error = devfs_get_cdevpriv((void **)&mem);
	if (error != 0)
		return (error);

	/* Grow object if necessary. */
	objsize = OFF_TO_IDX(*offset + size + PAGE_MASK);
	VM_OBJECT_LOCK(mem);
	if (objsize > mem->size) {
		/* Attempt to reserve swap space. */
		delta = ptoa(objsize - mem->size);
		if (!swap_reserve_by_cred(delta, mem->cred)) {
			VM_OBJECT_UNLOCK(mem);
			return (ENOMEM);
		}
		mem->charge += delta;
		mem->size = objsize;
	}
	vm_object_reference_locked(mem);
	*object = mem;
	VM_OBJECT_UNLOCK(mem);
	return (0);
}

static void
memfd_dtor(void *arg)
{
	vm_object_t mem;

	mem = arg;
	vm_object_deallocate(mem);
}

static int
memfd_modevent(module_t mod, int type, void *arg)
{
	static struct cdev *memfd;

	switch (type) {
	case MOD_LOAD:
		memfd = make_dev(&memfd_cdevsw, 0, UID_ROOT, GID_WHEEL, 0666,
		    "memfd");
		if (memfd == NULL) {
			printf("memfd: Failed to create /dev/memfd\n");
			return (ENXIO);
		}
		break;
	case MOD_UNLOAD:
		if (memfd != NULL)
			destroy_dev(memfd);
		break;
	case MOD_SHUTDOWN:
		break;
	default:
		return (EOPNOTSUPP);
	}
	return (0);
}

DEV_MODULE(memfd, memfd_modevent, NULL);