1GETDENTS(2) Linux Programmer's Manual GETDENTS(2)
2
6 getdents - get directory entries
7
9 int getdents(unsigned int fd, struct linux_dirent *dirp,
10 unsigned int count);
11 Note: There is no glibc wrapper for this system call; see NOTES.
13
15 This is not the function you are interested in. Look at readdir(3) for
16 the POSIX conforming C library interface. This page documents the bare
17 kernel system call interface.
18 The system call getdents() reads several linux_dirent structures from
20 the directory referred to by the open file descriptor fd into the buf‐
21 fer pointed to by dirp. The argument count specifies the size of that
22 buffer.
23 The linux_dirent structure is declared as follows:
25 struct linux_dirent {
27 unsigned long d_ino; /* Inode number */
28 unsigned long d_off; /* Offset to next linux_dirent */
29 unsigned short d_reclen; /* Length of this linux_dirent */
30 char d_name[]; /* Filename (null-terminated) */
31 /* length is actually (d_reclen - 2 -
32 offsetof(struct linux_dirent, d_name)) */
33 /*
34 char pad; // Zero padding byte
35 char d_type; // File type (only since Linux
36 // 2.6.4); offset is (d_reclen - 1)
37 */
38 }
40 d_ino is an inode number. d_off is the distance from the start of the
42 directory to the start of the next linux_dirent. d_reclen is the size
43 of this entire linux_dirent. d_name is a null-terminated filename.
44 d_type is a byte at the end of the structure that indicates the file
46 type. It contains one of the following values (defined in <dirent.h>):
47 DT_BLK This is a block device.
49 DT_CHR This is a character device.
51 DT_DIR This is a directory.
53 DT_FIFO This is a named pipe (FIFO).
55 DT_LNK This is a symbolic link.
57 DT_REG This is a regular file.
59 DT_SOCK This is a UNIX domain socket.
61 DT_UNKNOWN The file type is unknown.
63 The d_type field is implemented since Linux 2.6.4. It occupies a space
65 that was previously a zero-filled padding byte in the linux_dirent
66 structure. Thus, on kernels before 2.6.3, attempting to access this
67 field always provides the value 0 (DT_UNKNOWN).
68 Currently, only some file systems (among them: Btrfs, ext2, ext3, and
70 ext4) have full support for returning the file type in d_type. All
71 applications must properly handle a return of DT_UNKNOWN.
72
74 On success, the number of bytes read is returned. On end of directory,
75 0 is returned. On error, -1 is returned, and errno is set appropri‐
76 ately.
77
79 EBADF Invalid file descriptor fd.
80 EFAULT Argument points outside the calling process's address space.
82 EINVAL Result buffer is too small.
84 ENOENT No such directory.
86 ENOTDIR
88 File descriptor does not refer to a directory.
89
91 SVr4.
92
94 Glibc does not provide a wrapper for this system call; call it using
95 syscall(2). You will need to define the linux_dirent structure your‐
96 self. However, you probably want to use readdir(3) instead.
97 This call supersedes readdir(2).
99 The original Linux getdents() system call did not handle large file
101 systems and large file offsets. Consequently, Linux 2.4 added get‐
102 dents64(), with wider types for the d_ino and d_off fields employed in
103 the linux_dirent structure.
104
106 The program below demonstrates the use of getdents(). The following
107 output shows an example of what we see when running this program on an
108 ext2 directory:
109 $ ./a.out /testfs/
111 --------------- nread=120 ---------------
112 i-node# file type d_reclen d_off d_name
113 2 directory 16 12 .
114 2 directory 16 24 ..
115 11 directory 24 44 lost+found
116 12 regular 16 56 a
117 228929 directory 16 68 sub
118 16353 directory 16 80 sub2
119 130817 directory 16 4096 sub3
120 Program source
122 #define _GNU_SOURCE
124 #include <dirent.h> /* Defines DT_* constants */
125 #include <fcntl.h>
126 #include <stdio.h>
127 #include <unistd.h>
128 #include <stdlib.h>
129 #include <sys/stat.h>
130 #include <sys/syscall.h>
131 #define handle_error(msg) \
133 do { perror(msg); exit(EXIT_FAILURE); } while (0)
134 struct linux_dirent {
136 long d_ino;
137 off_t d_off;
138 unsigned short d_reclen;
139 char d_name[];
140 };
141 #define BUF_SIZE 1024
143 int
145 main(int argc, char *argv[])
146 {
147 int fd, nread;
148 char buf[BUF_SIZE];
149 struct linux_dirent *d;
150 int bpos;
151 char d_type;
152 fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
154 if (fd == -1)
155 handle_error("open");
156 for ( ; ; ) {
158 nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
159 if (nread == -1)
160 handle_error("getdents");
161 if (nread == 0)
163 break;
164 printf("--------------- nread=%d ---------------\n", nread);
166 printf("i-node# file type d_reclen d_off d_name\n");
167 for (bpos = 0; bpos < nread;) {
168 d = (struct linux_dirent *) (buf + bpos);
169 printf("%8ld ", d->d_ino);
170 d_type = *(buf + bpos + d->d_reclen - 1);
171 printf("%-10s ", (d_type == DT_REG) ? "regular" :
172 (d_type == DT_DIR) ? "directory" :
173 (d_type == DT_FIFO) ? "FIFO" :
174 (d_type == DT_SOCK) ? "socket" :
175 (d_type == DT_LNK) ? "symlink" :
176 (d_type == DT_BLK) ? "block dev" :
177 (d_type == DT_CHR) ? "char dev" : "???");
178 printf("%4d %10lld %s\n", d->d_reclen,
179 (long long) d->d_off, d->d_name);
180 bpos += d->d_reclen;
181 }
182 }
183 exit(EXIT_SUCCESS);
185 }
186
188 readdir(2), readdir(3)
189
191 This page is part of release 3.53 of the Linux man-pages project. A
192 description of the project, and information about reporting bugs, can
193 be found at http://www.kernel.org/doc/man-pages/.
194Linux 2012-08-03 GETDENTS(2)