broccofsその1(FUSEサンプル)です。

of_icon.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>
  Copyright (C) 2020       furandon_pig <furandon.pig@gmail.com>

  This program can be distributed under the terms of the GNU GPLv2.
  See the file COPYING.
*/

/*
 * gcc -g -o of_icon of_icon.c `pkg-config fuse3 --cflags --libs`
 */


#define FUSE_USE_VERSION 31

#include <fuse.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <stddef.h>
#include <assert.h>

static struct options {
	const char *filename;
	const char *contents;
	int count;
	int max;
	char **icons;
} options;

#define OPTION(t, p)                           \
    { t, offsetof(struct options, p), 1 }
static const struct fuse_opt option_spec[] = {
	FUSE_OPT_END
};

static void *hello_init(struct fuse_conn_info *conn,
			struct fuse_config *cfg)
{
	(void) conn;
	cfg->kernel_cache = 0;
	return NULL;
}

static int hello_getattr(const char *path, struct stat *stbuf,
			 struct fuse_file_info *fi)
{
	(void) fi;
	int res = 0;

	memset(stbuf, 0, sizeof(struct stat));
	if (strcmp(path, "/") == 0) {
		stbuf->st_mode = S_IFDIR | 0755;
		stbuf->st_nlink = 2;
	} else if (strcmp(path+1, options.filename) == 0) {
		stbuf->st_mode = S_IFREG | 0444;
		stbuf->st_nlink = 1;
		stbuf->st_size = strlen(options.contents);
	} else
		res = -ENOENT;

	return res;
}

static int hello_readdir(const char *path, void *buf, fuse_fill_dir_t filler,
			 off_t offset, struct fuse_file_info *fi,
			 enum fuse_readdir_flags flags)
{
	(void) offset;
	(void) fi;
	(void) flags;

	if (strcmp(path, "/") != 0)
		return -ENOENT;

	filler(buf, ".", NULL, 0, 0);
	filler(buf, "..", NULL, 0, 0);
	filler(buf, options.filename, NULL, 0, 0);

	return 0;
}

static int hello_open(const char *path, struct fuse_file_info *fi)
{
	if (strcmp(path+1, options.filename) != 0)
		return -ENOENT;

	if ((fi->flags & O_ACCMODE) != O_RDONLY)
		return -EACCES;

	return 0;
}

static int hello_read(const char *path, char *buf, size_t size, off_t offset,
		      struct fuse_file_info *fi)
{
	size_t len;
	(void) fi;
	if(strcmp(path+1, options.filename) != 0)
		return -ENOENT;

	len = strlen(options.contents);
	memcpy(buf, options.contents, len);

	if (++(options.count) >= options.max) {
		options.count = 0;
	}
	options.contents = options.icons[options.count];

	return size;
}

static const struct fuse_operations hello_oper = {
	.init           = hello_init,
	.getattr	= hello_getattr,
	.readdir	= hello_readdir,
	.open		= hello_open,
	.read		= hello_read,
};

int main(int argc, char *argv[])
{
	int ret;
	struct fuse_args args = FUSE_ARGS_INIT(argc, argv);

	options.filename = strdup("icon.txt");
	char *icons[] = {
		"OF_icon_1.png.resized.sixel",
		"OF_icon_2.png.resized.sixel",
		"OF_icon_3.png.resized.sixel",
		"OF_icon_4.png.resized.sixel",
		"OF_icon_5.png.resized.sixel",
		"OF_icon_6.png.resized.sixel",
		"OF_icon_7.png.resized.sixel",
		"OF_icon_8.png.resized.sixel",
		NULL
	};
	for (options.max = 0; icons[options.max] != NULL; options.max++)
		;
	options.icons = malloc(sizeof(char *) * options.count);
	if (options.icons) {
		FILE *fp;
		for (int i = 0; i < options.max; i++) {
			size_t sz = sizeof(char) * (BUFSIZ * 20);
			FILE *fp = fopen(icons[i], "r");
			options.icons[i] = malloc(sz);
			if (options.icons[i] != NULL && fp != NULL) {
				fread(options.icons[i], sz, 1, fp);
				//fclose(fp);
			}
		}
	}
	options.count = 0;
	options.contents = options.icons[0];

	/* Parse options */
	if (fuse_opt_parse(&args, &options, option_spec, NULL) == -1)
		return 1;

	ret = fuse_main(args.argc, args.argv, &hello_oper, NULL);
	fuse_opt_free_args(&args);
	return ret;
}