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
13 This is not the function you are interested in. Look at readdir(3) for
14 the POSIX conforming C library interface. This page documents the bare
15 kernel system call interface.
16 The system call getdents() reads several linux_dirent structures from
18 the directory referred to by the open file descriptor fd into the buf‐
19 fer pointed to by dirp. The argument count specifies the size of that
20 buffer.
21 The linux_dirent structure is declared as follows:
23 struct linux_dirent {
25 unsigned long d_ino; /* Inode number */
26 unsigned long d_off; /* Offset to next linux_dirent */
27 unsigned short d_reclen; /* Length of this linux_dirent */
28 char d_name[]; /* Filename (null-terminated) */
29 /* length is actually (d_reclen - 2 -
30 offsetof(struct linux_dirent, d_name) */
31 /*
32 char pad; // Zero padding byte */
33 char d_type; // File type (only since Linux 2.6.4;
34 // offset is (d_reclen - 1))
35 */
36 }
38 d_ino is an inode number. d_off is the distance from the start of the
40 directory to the start of the next linux_dirent. d_reclen is the size
41 of this entire linux_dirent. d_name is a null-terminated filename.
42 d_type is a byte at the end of the structure that indicates the file
44 type. It contains one of the following values (defined in <dirent.h>):
45 DT_BLK This is a block device.
47 DT_CHR This is a character device.
49 DT_DIR This is a directory.
51 DT_FIFO This is a named pipe (FIFO).
53 DT_LNK This is a symbolic link.
55 DT_REG This is a regular file.
57 DT_SOCK This is a Unix domain socket.
59 DT_UNKNOWN The file type is unknown.
61 The d_type field is implemented since Linux 2.6.4. It occupies a space
63 that was previously a zero-filled padding byte in the linux_dirent
64 structure. Thus, on kernels before 2.6.3, attempting to access this
65 field always provides the value 0 (DT_UNKNOWN).
66 Currently, only some file systems (among them: Btrfs, ext2, etx3, and
68 ext4) have full support for returning the file type in d_type. All
69 applications must properly handle a return of DT_UNKNOWN.
70
72 On success, the number of bytes read is returned. On end of directory,
73 0 is returned. On error, -1 is returned, and errno is set appropri‐
74 ately.
75
77 EBADF Invalid file descriptor fd.
78 EFAULT Argument points outside the calling process's address space.
80 EINVAL Result buffer is too small.
82 ENOENT No such directory.
84 ENOTDIR
86 File descriptor does not refer to a directory.
87
89 SVr4.
90
92 Glibc does not provide a wrapper for this system call; call it using
93 syscall(2). You will need to define the linux_dirent structure your‐
94 self.
95 This call supersedes readdir(2).
97 Warning: Result of the getdents() system call in 32 bit application on
99 64 bit OS doesn't have to be always correct, potentially the call
100 itself can fail.
101
103 The program below demonstrates the use of getdents(). The following
104 output shows an example of what we see when running this program on an
105 ext2 directory:
106 $ ./a.out /testfs/
108 --------------- nread=120 ---------------
109 i-node# file type d_reclen d_off d_name
110 2 directory 16 12 .
111 2 directory 16 24 ..
112 11 directory 24 44 lost+found
113 12 regular 16 56 a
114 228929 directory 16 68 sub
115 16353 directory 16 80 sub2
116 130817 directory 16 4096 sub3
117 Program source
119 #define _GNU_SOURCE
121 #include <dirent.h> /* Defines DT_* constants */
122 #include <fcntl.h>
123 #include <stdio.h>
124 #include <unistd.h>
125 #include <stdlib.h>
126 #include <sys/stat.h>
127 #include <sys/syscall.h>
128 #define handle_error(msg) \
130 do { perror(msg); exit(EXIT_FAILURE); } while (0)
131 struct linux_dirent {
133 long d_ino;
134 off_t d_off;
135 unsigned short d_reclen;
136 char d_name[];
137 };
138 #define BUF_SIZE 1024
140 int
142 main(int argc, char *argv[])
143 {
144 int fd, nread;
145 char buf[BUF_SIZE];
146 struct linux_dirent *d;
147 int bpos;
148 char d_type;
149 fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
151 if (fd == -1)
152 handle_error("open");
153 for ( ; ; ) {
155 nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
156 if (nread == -1)
157 handle_error("getdents");
158 if (nread == 0)
160 break;
161 printf("--------------- nread=%d ---------------\n", nread);
163 printf("i-node# file type d_reclen d_off d_name\n");
164 for (bpos = 0; bpos < nread;) {
165 d = (struct linux_dirent *) (buf + bpos);
166 printf("%8ld ", d->d_ino);
167 d_type = *(buf + bpos + d->d_reclen - 1);
168 printf("%-10s ", (d_type == DT_REG) ? "regular" :
169 (d_type == DT_DIR) ? "directory" :
170 (d_type == DT_FIFO) ? "FIFO" :
171 (d_type == DT_SOCK) ? "socket" :
172 (d_type == DT_LNK) ? "symlink" :
173 (d_type == DT_BLK) ? "block dev" :
174 (d_type == DT_CHR) ? "char dev" : "???");
175 printf("%4d %10lld %s\n", d->d_reclen,
176 (long long) d->d_off, (char *) d->d_name);
177 bpos += d->d_reclen;
178 }
179 }
180 exit(EXIT_SUCCESS);
182 }
183
185 readdir(2), readdir(3)
186
188 This page is part of release 3.22 of the Linux man-pages project. A
189 description of the project, and information about reporting bugs, can
190 be found at http://www.kernel.org/doc/man-pages/.
191Linux 2009-07-04 GETDENTS(2)