1GETDENTS(2) Linux Programmer's Manual GETDENTS(2)
2
6 getdents, getdents64 - get directory entries
7
9 long getdents(unsigned int fd, struct linux_dirent *dirp,
10 unsigned int count);
11 #define _GNU_SOURCE /* See feature_test_macros(7) */
13 #include <dirent.h>
14 ssize_t getdents64(int fd, void *dirp, size_t count);
16 Note: There is no glibc wrapper for getdents(); see NOTES.
18
20 These are not the interfaces you are interested in. Look at readdir(3)
21 for the POSIX-conforming C library interface. This page documents the
22 bare kernel system call interfaces.
23 getdents()
25 The system call getdents() reads several linux_dirent structures from
26 the directory referred to by the open file descriptor fd into the buf‐
27 fer pointed to by dirp. The argument count specifies the size of that
28 buffer.
29 The linux_dirent structure is declared as follows:
31 struct linux_dirent {
33 unsigned long d_ino; /* Inode number */
34 unsigned long d_off; /* Offset to next linux_dirent */
35 unsigned short d_reclen; /* Length of this linux_dirent */
36 char d_name[]; /* Filename (null-terminated) */
37 /* length is actually (d_reclen - 2 -
38 offsetof(struct linux_dirent, d_name)) */
39 /*
40 char pad; // Zero padding byte
41 char d_type; // File type (only since Linux
42 // 2.6.4); offset is (d_reclen - 1)
43 */
44 }
45 d_ino is an inode number. d_off is the distance from the start of the
47 directory to the start of the next linux_dirent. d_reclen is the size
48 of this entire linux_dirent. d_name is a null-terminated filename.
49 d_type is a byte at the end of the structure that indicates the file
51 type. It contains one of the following values (defined in <dirent.h>):
52 DT_BLK This is a block device.
54 DT_CHR This is a character device.
56 DT_DIR This is a directory.
58 DT_FIFO This is a named pipe (FIFO).
60 DT_LNK This is a symbolic link.
62 DT_REG This is a regular file.
64 DT_SOCK This is a UNIX domain socket.
66 DT_UNKNOWN The file type is unknown.
68 The d_type field is implemented since Linux 2.6.4. It occupies a space
70 that was previously a zero-filled padding byte in the linux_dirent
71 structure. Thus, on kernels up to and including 2.6.3, attempting to
72 access this field always provides the value 0 (DT_UNKNOWN).
73 Currently, only some filesystems (among them: Btrfs, ext2, ext3, and
75 ext4) have full support for returning the file type in d_type. All ap‐
76 plications must properly handle a return of DT_UNKNOWN.
77 getdents64()
79 The original Linux getdents() system call did not handle large filesys‐
80 tems and large file offsets. Consequently, Linux 2.4 added get‐
81 dents64(), with wider types for the d_ino and d_off fields. In addi‐
82 tion, getdents64() supports an explicit d_type field.
83 The getdents64() system call is like getdents(), except that its second
85 argument is a pointer to a buffer containing structures of the follow‐
86 ing type:
87 struct linux_dirent64 {
89 ino64_t d_ino; /* 64-bit inode number */
90 off64_t d_off; /* 64-bit offset to next structure */
91 unsigned short d_reclen; /* Size of this dirent */
92 unsigned char d_type; /* File type */
93 char d_name[]; /* Filename (null-terminated) */
94 };
95
97 On success, the number of bytes read is returned. On end of directory,
98 0 is returned. On error, -1 is returned, and errno is set appropri‐
99 ately.
100
102 EBADF Invalid file descriptor fd.
103 EFAULT Argument points outside the calling process's address space.
105 EINVAL Result buffer is too small.
107 ENOENT No such directory.
109 ENOTDIR
111 File descriptor does not refer to a directory.
112
114 SVr4.
115
117 Library support for getdents64() was added in glibc 2.30; there is no
118 glibc wrapper for getdents(). Calling getdents() (or getdents64() on
119 earlier glibc versions) requires the use of syscall(2). In that case
120 you will need to define the linux_dirent or linux_dirent64 structure
121 yourself.
122 Probably, you want to use readdir(3) instead of these system calls.
124 These calls supersede readdir(2).
126
128 The program below demonstrates the use of getdents(). The following
129 output shows an example of what we see when running this program on an
130 ext2 directory:
131 $ ./a.out /testfs/
133 --------------- nread=120 ---------------
134 inode# file type d_reclen d_off d_name
135 2 directory 16 12 .
136 2 directory 16 24 ..
137 11 directory 24 44 lost+found
138 12 regular 16 56 a
139 228929 directory 16 68 sub
140 16353 directory 16 80 sub2
141 130817 directory 16 4096 sub3
142 Program source
144 #define _GNU_SOURCE
146 #include <dirent.h> /* Defines DT_* constants */
147 #include <fcntl.h>
148 #include <stdint.h>
149 #include <stdio.h>
150 #include <unistd.h>
151 #include <stdlib.h>
152 #include <sys/stat.h>
153 #include <sys/syscall.h>
154 #define handle_error(msg) \
156 do { perror(msg); exit(EXIT_FAILURE); } while (0)
157 struct linux_dirent {
159 unsigned long d_ino;
160 off_t d_off;
161 unsigned short d_reclen;
162 char d_name[];
163 };
164 #define BUF_SIZE 1024
166 int
168 main(int argc, char *argv[])
169 {
170 int fd;
171 long nread;
172 char buf[BUF_SIZE];
173 struct linux_dirent *d;
174 char d_type;
175 fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
177 if (fd == -1)
178 handle_error("open");
179 for (;;) {
181 nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
182 if (nread == -1)
183 handle_error("getdents");
184 if (nread == 0)
186 break;
187 printf("--------------- nread=%d ---------------\n", nread);
189 printf("inode# file type d_reclen d_off d_name\n");
190 for (long bpos = 0; bpos < nread;) {
191 d = (struct linux_dirent *) (buf + bpos);
192 printf("%8ld ", d->d_ino);
193 d_type = *(buf + bpos + d->d_reclen - 1);
194 printf("%-10s ", (d_type == DT_REG) ? "regular" :
195 (d_type == DT_DIR) ? "directory" :
196 (d_type == DT_FIFO) ? "FIFO" :
197 (d_type == DT_SOCK) ? "socket" :
198 (d_type == DT_LNK) ? "symlink" :
199 (d_type == DT_BLK) ? "block dev" :
200 (d_type == DT_CHR) ? "char dev" : "???");
201 printf("%4d %10jd %s\n", d->d_reclen,
202 (intmax_t) d->d_off, d->d_name);
203 bpos += d->d_reclen;
204 }
205 }
206 exit(EXIT_SUCCESS);
208 }
209
211 readdir(2), readdir(3), inode(7)
212
214 This page is part of release 5.10 of the Linux man-pages project. A
215 description of the project, information about reporting bugs, and the
216 latest version of this page, can be found at
217 https://www.kernel.org/doc/man-pages/.
218Linux 2020-11-01 GETDENTS(2)