libfuse
cuse.c File Reference
#include <config.h>
#include <cuse_lowlevel.h>
#include <fuse_opt.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include "ioctl.h"

Detailed Description

This example demonstrates how to implement a character device in userspace ("CUSE"). This is only allowed for root. The character device should appear in /dev under the specified name. It can be tested with the cuse_client.c program.

Mount the file system with:

cuse -f --name=mydevice

You should now have a new /dev/mydevice character device. To "unmount" it, kill the "cuse" process.

To compile this example, run

gcc -Wall cuse.c `pkg-config fuse3 --cflags --libs` -o cuse

Source code

/*
CUSE example: Character device in Userspace
Copyright (C) 2008-2009 SUSE Linux Products GmbH
Copyright (C) 2008-2009 Tejun Heo <tj@kernel.org>
This program can be distributed under the terms of the GNU GPL.
See the file COPYING.
*/
#define FUSE_USE_VERSION 30
#include <config.h>
#include <cuse_lowlevel.h>
#include <fuse_opt.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include "ioctl.h"
static void *cusexmp_buf;
static size_t cusexmp_size;
static const char *usage =
"usage: cusexmp [options]\n"
"\n"
"options:\n"
" --help|-h print this help message\n"
" --maj=MAJ|-M MAJ device major number\n"
" --min=MIN|-m MIN device minor number\n"
" --name=NAME|-n NAME device name (mandatory)\n"
" -d -o debug enable debug output (implies -f)\n"
" -f foreground operation\n"
" -s disable multi-threaded operation\n"
"\n";
static int cusexmp_resize(size_t new_size)
{
void *new_buf;
if (new_size == cusexmp_size)
return 0;
new_buf = realloc(cusexmp_buf, new_size);
if (!new_buf && new_size)
return -ENOMEM;
if (new_size > cusexmp_size)
memset(new_buf + cusexmp_size, 0, new_size - cusexmp_size);
cusexmp_buf = new_buf;
cusexmp_size = new_size;
return 0;
}
static int cusexmp_expand(size_t new_size)
{
if (new_size > cusexmp_size)
return cusexmp_resize(new_size);
return 0;
}
static void cusexmp_open(fuse_req_t req, struct fuse_file_info *fi)
{
fuse_reply_open(req, fi);
}
static void cusexmp_read(fuse_req_t req, size_t size, off_t off,
struct fuse_file_info *fi)
{
(void)fi;
if (off >= cusexmp_size)
off = cusexmp_size;
if (size > cusexmp_size - off)
size = cusexmp_size - off;
fuse_reply_buf(req, cusexmp_buf + off, size);
}
static void cusexmp_write(fuse_req_t req, const char *buf, size_t size,
off_t off, struct fuse_file_info *fi)
{
(void)fi;
if (cusexmp_expand(off + size)) {
fuse_reply_err(req, ENOMEM);
return;
}
memcpy(cusexmp_buf + off, buf, size);
fuse_reply_write(req, size);
}
static void fioc_do_rw(fuse_req_t req, void *addr, const void *in_buf,
size_t in_bufsz, size_t out_bufsz, int is_read)
{
const struct fioc_rw_arg *arg;
struct iovec in_iov[2], out_iov[3], iov[3];
size_t cur_size;
/* read in arg */
in_iov[0].iov_base = addr;
in_iov[0].iov_len = sizeof(*arg);
if (!in_bufsz) {
fuse_reply_ioctl_retry(req, in_iov, 1, NULL, 0);
return;
}
arg = in_buf;
in_buf += sizeof(*arg);
in_bufsz -= sizeof(*arg);
/* prepare size outputs */
out_iov[0].iov_base =
addr + offsetof(struct fioc_rw_arg, prev_size);
out_iov[0].iov_len = sizeof(arg->prev_size);
out_iov[1].iov_base =
addr + offsetof(struct fioc_rw_arg, new_size);
out_iov[1].iov_len = sizeof(arg->new_size);
/* prepare client buf */
if (is_read) {
out_iov[2].iov_base = arg->buf;
out_iov[2].iov_len = arg->size;
if (!out_bufsz) {
fuse_reply_ioctl_retry(req, in_iov, 1, out_iov, 3);
return;
}
} else {
in_iov[1].iov_base = arg->buf;
in_iov[1].iov_len = arg->size;
if (arg->size && !in_bufsz) {
fuse_reply_ioctl_retry(req, in_iov, 2, out_iov, 2);
return;
}
}
/* we're all set */
cur_size = cusexmp_size;
iov[0].iov_base = &cur_size;
iov[0].iov_len = sizeof(cur_size);
iov[1].iov_base = &cusexmp_size;
iov[1].iov_len = sizeof(cusexmp_size);
if (is_read) {
size_t off = arg->offset;
size_t size = arg->size;
if (off >= cusexmp_size)
off = cusexmp_size;
if (size > cusexmp_size - off)
size = cusexmp_size - off;
iov[2].iov_base = cusexmp_buf + off;
iov[2].iov_len = size;
fuse_reply_ioctl_iov(req, size, iov, 3);
} else {
if (cusexmp_expand(arg->offset + in_bufsz)) {
fuse_reply_err(req, ENOMEM);
return;
}
memcpy(cusexmp_buf + arg->offset, in_buf, in_bufsz);
fuse_reply_ioctl_iov(req, in_bufsz, iov, 2);
}
}
static void cusexmp_ioctl(fuse_req_t req, int cmd, void *arg,
struct fuse_file_info *fi, unsigned flags,
const void *in_buf, size_t in_bufsz, size_t out_bufsz)
{
int is_read = 0;
(void)fi;
if (flags & FUSE_IOCTL_COMPAT) {
fuse_reply_err(req, ENOSYS);
return;
}
switch (cmd) {
case FIOC_GET_SIZE:
if (!out_bufsz) {
struct iovec iov = { arg, sizeof(size_t) };
fuse_reply_ioctl_retry(req, NULL, 0, &iov, 1);
} else
fuse_reply_ioctl(req, 0, &cusexmp_size,
sizeof(cusexmp_size));
break;
case FIOC_SET_SIZE:
if (!in_bufsz) {
struct iovec iov = { arg, sizeof(size_t) };
fuse_reply_ioctl_retry(req, &iov, 1, NULL, 0);
} else {
cusexmp_resize(*(size_t *)in_buf);
fuse_reply_ioctl(req, 0, NULL, 0);
}
break;
case FIOC_READ:
is_read = 1;
/* no break */
case FIOC_WRITE:
fioc_do_rw(req, arg, in_buf, in_bufsz, out_bufsz, is_read);
break;
default:
fuse_reply_err(req, EINVAL);
}
}
struct cusexmp_param {
unsigned major;
unsigned minor;
char *dev_name;
int is_help;
};
#define CUSEXMP_OPT(t, p) { t, offsetof(struct cusexmp_param, p), 1 }
static const struct fuse_opt cusexmp_opts[] = {
CUSEXMP_OPT("-M %u", major),
CUSEXMP_OPT("--maj=%u", major),
CUSEXMP_OPT("-m %u", minor),
CUSEXMP_OPT("--min=%u", minor),
CUSEXMP_OPT("-n %s", dev_name),
CUSEXMP_OPT("--name=%s", dev_name),
FUSE_OPT_KEY("-h", 0),
FUSE_OPT_KEY("--help", 0),
};
static int cusexmp_process_arg(void *data, const char *arg, int key,
struct fuse_args *outargs)
{
struct cusexmp_param *param = data;
(void)outargs;
(void)arg;
switch (key) {
case 0:
param->is_help = 1;
fprintf(stderr, "%s", usage);
return fuse_opt_add_arg(outargs, "-ho");
default:
return 1;
}
}
static const struct cuse_lowlevel_ops cusexmp_clop = {
.open = cusexmp_open,
.read = cusexmp_read,
.write = cusexmp_write,
.ioctl = cusexmp_ioctl,
};
int main(int argc, char **argv)
{
struct fuse_args args = FUSE_ARGS_INIT(argc, argv);
struct cusexmp_param param = { 0, 0, NULL, 0 };
char dev_name[128] = "DEVNAME=";
const char *dev_info_argv[] = { dev_name };
struct cuse_info ci;
if (fuse_opt_parse(&args, &param, cusexmp_opts, cusexmp_process_arg)) {
printf("failed to parse option\n");
return 1;
}
if (!param.is_help) {
if (!param.dev_name) {
fprintf(stderr, "Error: device name missing\n");
return 1;
}
strncat(dev_name, param.dev_name, sizeof(dev_name) - 9);
}
memset(&ci, 0, sizeof(ci));
ci.dev_major = param.major;
ci.dev_minor = param.minor;
ci.dev_info_argc = 1;
ci.dev_info_argv = dev_info_argv;
ci.flags = CUSE_UNRESTRICTED_IOCTL;
return cuse_lowlevel_main(args.argc, args.argv, &ci, &cusexmp_clop,
NULL);
}