1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * memfd test file-system
4 * This file uses FUSE to create a dummy file-system with only one file /memfd.
5 * This file is read-only and takes 1s per read.
6 *
7 * This file-system is used by the memfd test-cases to force the kernel to pin
8 * pages during reads(). Due to the 1s delay of this file-system, this is a
9 * nice way to test race-conditions against get_user_pages() in the kernel.
10 *
11 * We use direct_io==1 to force the kernel to use direct-IO for this
12 * file-system.
13 */
14
15 #define FUSE_USE_VERSION 26
16
17 #include <fuse.h>
18 #include <stdio.h>
19 #include <string.h>
20 #include <errno.h>
21 #include <fcntl.h>
22 #include <unistd.h>
23
24 static const char memfd_content[] = "memfd-example-content";
25 static const char memfd_path[] = "/memfd";
26
27 static int memfd_getattr(const char *path, struct stat *st)
28 {
29 memset(st, 0, sizeof(*st));
30
31 if (!strcmp(path, "/")) {
32 st->st_mode = S_IFDIR | 0755;
33 st->st_nlink = 2;
34 } else if (!strcmp(path, memfd_path)) {
35 st->st_mode = S_IFREG | 0444;
36 st->st_nlink = 1;
37 st->st_size = strlen(memfd_content);
38 } else {
39 return -ENOENT;
40 }
41
42 return 0;
43 }
44
45 static int memfd_readdir(const char *path,
46 void *buf,
47 fuse_fill_dir_t filler,
48 off_t offset,
49 struct fuse_file_info *fi)
50 {
51 if (strcmp(path, "/"))
52 return -ENOENT;
53
54 filler(buf, ".", NULL, 0);
55 filler(buf, "..", NULL, 0);
56 filler(buf, memfd_path + 1, NULL, 0);
57
58 return 0;
59 }
60
61 static int memfd_open(const char *path, struct fuse_file_info *fi)
62 {
63 if (strcmp(path, memfd_path))
64 return -ENOENT;
65
66 if ((fi->flags & 3) != O_RDONLY)
67 return -EACCES;
68
69 /* force direct-IO */
70 fi->direct_io = 1;
71
72 return 0;
73 }
74
75 static int memfd_read(const char *path,
76 char *buf,
77 size_t size,
78 off_t offset,
79 struct fuse_file_info *fi)
80 {
81 size_t len;
82
83 if (strcmp(path, memfd_path) != 0)
84 return -ENOENT;
85
86 sleep(1);
87
88 len = strlen(memfd_content);
89 if (offset < len) {
90 if (offset + size > len)
91 size = len - offset;
92
93 memcpy(buf, memfd_content + offset, size);
94 } else {
95 size = 0;
96 }
97
98 return size;
99 }
100
101 static struct fuse_operations memfd_ops = {
102 .getattr = memfd_getattr,
103 .readdir = memfd_readdir,
104 .open = memfd_open,
105 .read = memfd_read,
106 };
107
108 int main(int argc, char *argv[])
109 {
110 return fuse_main(argc, argv, &memfd_ops, NULL);
111 }
112
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