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, ext3, 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
99 The program below demonstrates the use of getdents(). The following
100 output shows an example of what we see when running this program on an
101 ext2 directory:
102 $ ./a.out /testfs/
104 --------------- nread=120 ---------------
105 i-node# file type d_reclen d_off d_name
106 2 directory 16 12 .
107 2 directory 16 24 ..
108 11 directory 24 44 lost+found
109 12 regular 16 56 a
110 228929 directory 16 68 sub
111 16353 directory 16 80 sub2
112 130817 directory 16 4096 sub3
113 Program source
115 #define _GNU_SOURCE
117 #include <dirent.h> /* Defines DT_* constants */
118 #include <fcntl.h>
119 #include <stdio.h>
120 #include <unistd.h>
121 #include <stdlib.h>
122 #include <sys/stat.h>
123 #include <sys/syscall.h>
124 #define handle_error(msg) \
126 do { perror(msg); exit(EXIT_FAILURE); } while (0)
127 struct linux_dirent {
129 long d_ino;
130 off_t d_off;
131 unsigned short d_reclen;
132 char d_name[];
133 };
134 #define BUF_SIZE 1024
136 int
138 main(int argc, char *argv[])
139 {
140 int fd, nread;
141 char buf[BUF_SIZE];
142 struct linux_dirent *d;
143 int bpos;
144 char d_type;
145 fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
147 if (fd == -1)
148 handle_error("open");
149 for ( ; ; ) {
151 nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
152 if (nread == -1)
153 handle_error("getdents");
154 if (nread == 0)
156 break;
157 printf("--------------- nread=%d ---------------\n", nread);
159 printf("i-node# file type d_reclen d_off d_name\n");
160 for (bpos = 0; bpos < nread;) {
161 d = (struct linux_dirent *) (buf + bpos);
162 printf("%8ld ", d->d_ino);
163 d_type = *(buf + bpos + d->d_reclen - 1);
164 printf("%-10s ", (d_type == DT_REG) ? "regular" :
165 (d_type == DT_DIR) ? "directory" :
166 (d_type == DT_FIFO) ? "FIFO" :
167 (d_type == DT_SOCK) ? "socket" :
168 (d_type == DT_LNK) ? "symlink" :
169 (d_type == DT_BLK) ? "block dev" :
170 (d_type == DT_CHR) ? "char dev" : "???");
171 printf("%4d %10lld %s\n", d->d_reclen,
172 (long long) d->d_off, (char *) d->d_name);
173 bpos += d->d_reclen;
174 }
175 }
176 exit(EXIT_SUCCESS);
178 }
179
181 readdir(2), readdir(3)
182
184 This page is part of release 3.25 of the Linux man-pages project. A
185 description of the project, and information about reporting bugs, can
186 be found at http://www.kernel.org/doc/man-pages/.
187Linux 2009-07-04 GETDENTS(2)