// SPDX-License-Identifier: GPL-2.0
/*
 * memfd test file-system
 * This file uses FUSE to create a dummy file-system with only one file /memfd.
 * This file is read-only and takes 1s per read.
 *
 * This file-system is used by the memfd test-cases to force the kernel to pin
 * pages during reads(). Due to the 1s delay of this file-system, this is a
 * nice way to test race-conditions against get_user_pages() in the kernel.
 *
 * We use direct_io==1 to force the kernel to use direct-IO for this
 * file-system.
 */

#define FUSE_USE_VERSION 26

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>

static const char memfd_content[] = "memfd-example-content";
static const char memfd_path[] = "/memfd";

static int memfd_getattr(const char *path, struct stat *st)
{
        memset(st, 0, sizeof(*st));

        if (!strcmp(path, "/")) {
                st->st_mode = S_IFDIR | 0755;
                st->st_nlink = 2;
        } else if (!strcmp(path, memfd_path)) {
                st->st_mode = S_IFREG | 0444;
                st->st_nlink = 1;
                st->st_size = strlen(memfd_content);
        } else {
                return -ENOENT;
        }

        return 0;
}

static int memfd_readdir(const char *path,
                         void *buf,
                         fuse_fill_dir_t filler,
                         off_t offset,
                         struct fuse_file_info *fi)
{
        if (strcmp(path, "/"))
                return -ENOENT;

        filler(buf, ".", NULL, 0);
        filler(buf, "..", NULL, 0);
        filler(buf, memfd_path + 1, NULL, 0);

        return 0;
}

static int memfd_open(const char *path, struct fuse_file_info *fi)
{
        if (strcmp(path, memfd_path))
                return -ENOENT;

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

        /* force direct-IO */
        fi->direct_io = 1;

        return 0;
}

static int memfd_read(const char *path,
                      char *buf,
                      size_t size,
                      off_t offset,
                      struct fuse_file_info *fi)
{
        size_t len;

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

        sleep(1);

        len = strlen(memfd_content);
        if (offset < len) {
                if (offset + size > len)
                        size = len - offset;

                memcpy(buf, memfd_content + offset, size);
        } else {
                size = 0;
        }

        return size;
}

static struct fuse_operations memfd_ops = {
        .getattr        = memfd_getattr,
        .readdir        = memfd_readdir,
        .open           = memfd_open,
        .read           = memfd_read,
};

int main(int argc, char *argv[])
{
        return fuse_main(argc, argv, &memfd_ops, NULL);
}