.\" $OpenBSD: fuse_main.3,v 1.3 2018/07/05 10:29:36 helg Exp $
.\"
.\" Copyright (c) 2013 Sylvestre Gallon <ccna.syl@gmail.com>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: July 5 2018 $
.Dt FUSE_MAIN 3
.Os
.Sh NAME
.Nm fuse_main ,
.Nm fuse_version ,
.Nm fuse_new ,
.Nm fuse_parse_cmdline ,
.Nm fuse_mount ,
.Nm fuse_get_session ,
.Nm fuse_get_context ,
.Nm fuse_is_lib_option ,
.Nm fuse_loop ,
.Nm fuse_loop_mt ,
.Nm fuse_chan_fd ,
.Nm fuse_unmount ,
.Nm fuse_daemonize ,
.Nm fuse_destroy ,
.Nm fuse_teardown
.Nd FUSE implementation routines
.Sh SYNOPSIS
.In fuse.h
.Ft int
.Fn fuse_main "int argc" "char **argv" "const struct fuse_operations *ops" \
    "void *data"
.Ft int
.Fn fuse_version "void"
.Ft struct fuse *
.Fn fuse_new "struct fuse_chan *fc" "struct fuse_args *args" \
    "const struct fuse_operations *ops" "size_t size" "void *userdata"
.Ft int
.Fn fuse_parse_cmdline "struct fuse_args *args" "char **mp" "int *mt" "int *fg"
.Ft struct fuse_chan *
.Fn fuse_mount "const char *dir" "struct fuse_args *args"
.Ft struct fuse_session *
.Fn fuse_get_session "struct fuse *f"
.Ft struct fuse_context *
.Fn fuse_get_context "void"
.Ft int
.Fn fuse_is_lib_option "const char *opt"
.Ft int
.Fn fuse_loop "struct fuse *fuse"
.Ft int
.Fn fuse_loop_mt "struct fuse *fuse"
.Ft int
.Fn fuse_chan_fd "struct fuse_chan *ch"
.Ft void
.Fn fuse_unmount "const char *dir" "struct fuse_chan *ch"
.Ft int
.Fn fuse_daemonize "int foreground"
.Ft void
.Fn fuse_destroy "struct fuse *f"
.Ft void
.Fn fuse_teardown "struct fuse *f" "char *mp"
.Sh DESCRIPTION
The FUSE library provides routines to implement a filesystem in userspace.
.Pp
There are two ways of implementing a FUSE filesystem:
by calling only
.Fn fuse_main
and passing this function the
.Em ops
argument containing all the callbacks of the filesystem,
or by using the other functions,
as detailed below.
.Pp
.Fn fuse_version
returns the FUSE version number.
.Pp
.Fn fuse_new
returns a
.Fa struct fuse
that will be needed by
.Fn fuse_loop .
.Pp
.Fn fuse_parse_cmdline
parses the
.Fa struct fuse_args
given by the user and will set
.Fa mp
with a char * containing the mountpoint directory.
.Pp
.Fn fuse_mount
looks for an empty
.Xr fuse 4
device to create a connection.
If this function finds an available device it will open it for FUSE
communication with the FUSE VFS driver and will mount the filesystem.
This function will return a
.Fa struct fuse_chan
that will be needed by
.Fn fuse_new .
.Pp
.Fn fuse_get_session
returns a pointer to the structure
.Fa fuse_session
contained in a
.Fa struct fuse .
.Pp
.Fn fuse_get_context
returns a pointer to the structure
.Fa fuse_context .
The returned fuse_context is only available during the lifetime of a FUSE
operation.
.Pp
.Fn fuse_is_lib_option
checks if the string
.Fa opt
is an option handled by libfuse or by the FUSE client.
It returns 1 if it is handled by the lib and 0 otherwise.
.Pp
.Fn fuse_loop_mt
is unsupported.
.Pp
.Fn fuse_loop
is the main loop of a FUSE program.
This function looks for FUSE requests from the kernel and responds to them
using the
.Fa struct fuse_operation
present in the structure
.Fa fuse .
It will return only if something goes wrong
or if the kernel sends a
.Fa FUSE_DESTROY
opcode to libfuse.
.Pp
.Fn fuse_chan_fd
returns the filedescriptor used by the given
.Fa fuse_chan
structure.
.Pp
.Fn fuse_unmount
unmounts the
.Fa dir
mountpoint.
.Pp
.Fn fuse_daemonize
daemonises the FUSE library.
It runs the FUSE program in the background,
whilst continuing to handle kernel filesystem opcodes.
.Pp
.Fn fuse_destroy
is currently undocumented.
.Pp
.Fn fuse_teardown
calls
.Fn fuse_unmount
and
.Fn fuse_destroy .
.Sh EXAMPLES
Here is a simple example of a FUSE implementation:
.Bd -literal
#include <errno.h>
#include <fuse.h>
#include <string.h>

static int
fs_readdir(const char *path, void *data, fuse_fill_dir_t filler,
    off_t off, struct fuse_file_info *ffi)
{
	if (strcmp(path, "/") != 0)
		return (-ENOENT);

	filler(data, ".", NULL, 0);
	filler(data, "..", NULL, 0);
	filler(data, "file", NULL, 0);
	return (0);
}

static int
fs_read(const char *path, char *buf, size_t size, off_t off,
    struct fuse_file_info *ffi)
{
	if (off >= 5)
		return (0);

	size = 5 - off;
	memcpy(buf, "data." + off, size);
	return (size);
}

static int
fs_open(const char *path, struct fuse_file_info *ffi)
{
	if (strncmp(path, "/file", 10) != 0)
		return (-ENOENT);

	if ((ffi->flags & 3) != O_RDONLY)
		return (-EACCES);

	return (0);
}

static int
fs_getattr(const char *path, struct stat *st)
{
	if (strcmp(path, "/") == 0) {
		st->st_blksize = 512;
		st->st_mode = 0755;
		st->st_nlink = 2;
	} else if (strcmp(path, "/file") == 0) {
		st->st_mode = 0644;
		st->st_blksize = 512;
		st->st_nlink = 1;
		st->st_size = 5;
	} else {
		return (-ENOENT);
	}

	return (0);
}

struct fuse_operations fsops = {
	.readdir = fs_readdir,
	.read = fs_read,
	.open = fs_open,
	.getattr = fs_getattr,
};

int
main(int ac, char **av)
{
	return (fuse_main(ac, av, &fsops, NULL));
}
.Ed
.Sh SEE ALSO
.Xr fuse 4
.Sh STANDARDS
The original FUSE specification can be found at
.Lk http://libfuse.github.io/doxygen/ .
The original implementation can be found at
.Lk https://github.com/libfuse/libfuse/ .
.Sh HISTORY
The FUSE library first appeared in
.Ox 5.4 .
.Sh BUGS
This man page is woefully incomplete.