1GETDENTS(2) Linux Programmer's Manual GETDENTS(2)
2
6 getdents, getdents64 - get directory entries
7
9 int getdents(unsigned int fd, struct linux_dirent *dirp,
10 unsigned int count);
11 int getdents64(unsigned int fd, struct linux_dirent64 *dirp,
12 unsigned int count);
13 Note: There is no glibc wrapper for getdents(); see NOTES.
15
17 These are not the interfaces you are interested in. Look at readdir(3)
18 for the POSIX-conforming C library interface. This page documents the
19 bare kernel system call interfaces.
20 getdents()
22 The system call getdents() reads several linux_dirent structures from
23 the directory referred to by the open file descriptor fd into the buf‐
24 fer pointed to by dirp. The argument count specifies the size of that
25 buffer.
26 The linux_dirent structure is declared as follows:
28 struct linux_dirent {
30 unsigned long d_ino; /* Inode number */
31 unsigned long d_off; /* Offset to next linux_dirent */
32 unsigned short d_reclen; /* Length of this linux_dirent */
33 char d_name[]; /* Filename (null-terminated) */
34 /* length is actually (d_reclen - 2 -
35 offsetof(struct linux_dirent, d_name)) */
36 /*
37 char pad; // Zero padding byte
38 char d_type; // File type (only since Linux
39 // 2.6.4); offset is (d_reclen - 1)
40 */
41 }
42 d_ino is an inode number. d_off is the distance from the start of the
44 directory to the start of the next linux_dirent. d_reclen is the size
45 of this entire linux_dirent. d_name is a null-terminated filename.
46 d_type is a byte at the end of the structure that indicates the file
48 type. It contains one of the following values (defined in <dirent.h>):
49 DT_BLK This is a block device.
51 DT_CHR This is a character device.
53 DT_DIR This is a directory.
55 DT_FIFO This is a named pipe (FIFO).
57 DT_LNK This is a symbolic link.
59 DT_REG This is a regular file.
61 DT_SOCK This is a UNIX domain socket.
63 DT_UNKNOWN The file type is unknown.
65 The d_type field is implemented since Linux 2.6.4. It occupies a space
67 that was previously a zero-filled padding byte in the linux_dirent
68 structure. Thus, on kernels up to and including 2.6.3, attempting to
69 access this field always provides the value 0 (DT_UNKNOWN).
70 Currently, only some filesystems (among them: Btrfs, ext2, ext3, and
72 ext4) have full support for returning the file type in d_type. All
73 applications must properly handle a return of DT_UNKNOWN.
74 getdents64()
76 The original Linux getdents() system call did not handle large filesys‐
77 tems and large file offsets. Consequently, Linux 2.4 added get‐
78 dents64(), with wider types for the d_ino and d_off fields. In addi‐
79 tion, getdents64() supports an explicit d_type field.
80 The getdents64() system call is like getdents(), except that its second
82 argument is a pointer to a buffer containing structures of the follow‐
83 ing type:
84 struct linux_dirent64 {
86 ino64_t d_ino; /* 64-bit inode number */
87 off64_t d_off; /* 64-bit offset to next structure */
88 unsigned short d_reclen; /* Size of this dirent */
89 unsigned char d_type; /* File type */
90 char d_name[]; /* Filename (null-terminated) */
91 };
92
94 On success, the number of bytes read is returned. On end of directory,
95 0 is returned. On error, -1 is returned, and errno is set appropri‐
96 ately.
97
99 EBADF Invalid file descriptor fd.
100 EFAULT Argument points outside the calling process's address space.
102 EINVAL Result buffer is too small.
104 ENOENT No such directory.
106 ENOTDIR
108 File descriptor does not refer to a directory.
109
111 SVr4.
112
114 Library support for getdents64() was added in glibc 2.30; there is no
115 glibc wrapper for getdents(). Calling getdents() (or getdents64() on
116 earlier glibc versions) requires the use of syscall(2). In that case
117 you will need to define the linux_dirent or linux_dirent64 structure
118 yourself.
119 Probably, you probably want to use readdir(3) instead of these system
121 calls.
122 These calls supersede readdir(2).
124
126 The program below demonstrates the use of getdents(). The following
127 output shows an example of what we see when running this program on an
128 ext2 directory:
129 $ ./a.out /testfs/
131 --------------- nread=120 ---------------
132 inode# file type d_reclen d_off d_name
133 2 directory 16 12 .
134 2 directory 16 24 ..
135 11 directory 24 44 lost+found
136 12 regular 16 56 a
137 228929 directory 16 68 sub
138 16353 directory 16 80 sub2
139 130817 directory 16 4096 sub3
140 Program source
142 #define _GNU_SOURCE
144 #include <dirent.h> /* Defines DT_* constants */
145 #include <fcntl.h>
146 #include <stdio.h>
147 #include <unistd.h>
148 #include <stdlib.h>
149 #include <sys/stat.h>
150 #include <sys/syscall.h>
151 #define handle_error(msg) \
153 do { perror(msg); exit(EXIT_FAILURE); } while (0)
154 struct linux_dirent {
156 unsigned long d_ino;
157 off_t d_off;
158 unsigned short d_reclen;
159 char d_name[];
160 };
161 #define BUF_SIZE 1024
163 int
165 main(int argc, char *argv[])
166 {
167 int fd, nread;
168 char buf[BUF_SIZE];
169 struct linux_dirent *d;
170 int bpos;
171 char d_type;
172 fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
174 if (fd == -1)
175 handle_error("open");
176 for ( ; ; ) {
178 nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
179 if (nread == -1)
180 handle_error("getdents");
181 if (nread == 0)
183 break;
184 printf("--------------- nread=%d ---------------\n", nread);
186 printf("inode# file type d_reclen d_off d_name\n");
187 for (bpos = 0; bpos < nread;) {
188 d = (struct linux_dirent *) (buf + bpos);
189 printf("%8ld ", d->d_ino);
190 d_type = *(buf + bpos + d->d_reclen - 1);
191 printf("%-10s ", (d_type == DT_REG) ? "regular" :
192 (d_type == DT_DIR) ? "directory" :
193 (d_type == DT_FIFO) ? "FIFO" :
194 (d_type == DT_SOCK) ? "socket" :
195 (d_type == DT_LNK) ? "symlink" :
196 (d_type == DT_BLK) ? "block dev" :
197 (d_type == DT_CHR) ? "char dev" : "???");
198 printf("%4d %10lld %s\n", d->d_reclen,
199 (long long) d->d_off, d->d_name);
200 bpos += d->d_reclen;
201 }
202 }
203 exit(EXIT_SUCCESS);
205 }
206
208 readdir(2), readdir(3), inode(7)
209
211 This page is part of release 5.07 of the Linux man-pages project. A
212 description of the project, information about reporting bugs, and the
213 latest version of this page, can be found at
214 https://www.kernel.org/doc/man-pages/.
215Linux 2020-06-09 GETDENTS(2)