1GETDENTS(2) Linux Programmer's Manual GETDENTS(2)
2
6 getdents, getdents64 - get directory entries
7
9 #include <sys/syscall.h> /* Definition of SYS_* constants */
10 #include <unistd.h>
11 long syscall(SYS_getdents, unsigned int fd, struct linux_dirent *dirp,
13 unsigned int count);
14 #define _GNU_SOURCE /* See feature_test_macros(7) */
16 #include <dirent.h>
17 ssize_t getdents64(int fd, void *dirp, size_t count);
19 Note: glibc provides no wrapper for getdents(), necessitating the use
21 of syscall(2).
22 Note: There is no definition of struct linux_dirent in glibc; see
24 NOTES.
25
27 These are not the interfaces you are interested in. Look at readdir(3)
28 for the POSIX-conforming C library interface. This page documents the
29 bare kernel system call interfaces.
30 getdents()
32 The system call getdents() reads several linux_dirent structures from
33 the directory referred to by the open file descriptor fd into the buf‐
34 fer pointed to by dirp. The argument count specifies the size of that
35 buffer.
36 The linux_dirent structure is declared as follows:
38 struct linux_dirent {
40 unsigned long d_ino; /* Inode number */
41 unsigned long d_off; /* Offset to next linux_dirent */
42 unsigned short d_reclen; /* Length of this linux_dirent */
43 char d_name[]; /* Filename (null-terminated) */
44 /* length is actually (d_reclen - 2 -
45 offsetof(struct linux_dirent, d_name)) */
46 /*
47 char pad; // Zero padding byte
48 char d_type; // File type (only since Linux
49 // 2.6.4); offset is (d_reclen - 1)
50 */
51 }
52 d_ino is an inode number. d_off is the distance from the start of the
54 directory to the start of the next linux_dirent. d_reclen is the size
55 of this entire linux_dirent. d_name is a null-terminated filename.
56 d_type is a byte at the end of the structure that indicates the file
58 type. It contains one of the following values (defined in <dirent.h>):
59 DT_BLK This is a block device.
61 DT_CHR This is a character device.
63 DT_DIR This is a directory.
65 DT_FIFO This is a named pipe (FIFO).
67 DT_LNK This is a symbolic link.
69 DT_REG This is a regular file.
71 DT_SOCK This is a UNIX domain socket.
73 DT_UNKNOWN The file type is unknown.
75 The d_type field is implemented since Linux 2.6.4. It occupies a space
77 that was previously a zero-filled padding byte in the linux_dirent
78 structure. Thus, on kernels up to and including 2.6.3, attempting to
79 access this field always provides the value 0 (DT_UNKNOWN).
80 Currently, only some filesystems (among them: Btrfs, ext2, ext3, and
82 ext4) have full support for returning the file type in d_type. All ap‐
83 plications must properly handle a return of DT_UNKNOWN.
84 getdents64()
86 The original Linux getdents() system call did not handle large filesys‐
87 tems and large file offsets. Consequently, Linux 2.4 added get‐
88 dents64(), with wider types for the d_ino and d_off fields. In addi‐
89 tion, getdents64() supports an explicit d_type field.
90 The getdents64() system call is like getdents(), except that its second
92 argument is a pointer to a buffer containing structures of the follow‐
93 ing type:
94 struct linux_dirent64 {
96 ino64_t d_ino; /* 64-bit inode number */
97 off64_t d_off; /* 64-bit offset to next structure */
98 unsigned short d_reclen; /* Size of this dirent */
99 unsigned char d_type; /* File type */
100 char d_name[]; /* Filename (null-terminated) */
101 };
102
104 On success, the number of bytes read is returned. On end of directory,
105 0 is returned. On error, -1 is returned, and errno is set to indicate
106 the error.
107
109 EBADF Invalid file descriptor fd.
110 EFAULT Argument points outside the calling process's address space.
112 EINVAL Result buffer is too small.
114 ENOENT No such directory.
116 ENOTDIR
118 File descriptor does not refer to a directory.
119
121 SVr4.
122
124 Library support for getdents64() was added in glibc 2.30; Glibc does
125 not provide a wrapper for getdents(); call getdents() (or getdents64()
126 on earlier glibc versions) using syscall(2). In that case you will
127 need to define the linux_dirent or linux_dirent64 structure yourself.
128 Probably, you want to use readdir(3) instead of these system calls.
130 These calls supersede readdir(2).
132
134 The program below demonstrates the use of getdents(). The following
135 output shows an example of what we see when running this program on an
136 ext2 directory:
137 $ ./a.out /testfs/
139 --------------- nread=120 ---------------
140 inode# file type d_reclen d_off d_name
141 2 directory 16 12 .
142 2 directory 16 24 ..
143 11 directory 24 44 lost+found
144 12 regular 16 56 a
145 228929 directory 16 68 sub
146 16353 directory 16 80 sub2
147 130817 directory 16 4096 sub3
148 Program source
150 #define _GNU_SOURCE
152 #include <dirent.h> /* Defines DT_* constants */
153 #include <fcntl.h>
154 #include <stdint.h>
155 #include <stdio.h>
156 #include <unistd.h>
157 #include <stdlib.h>
158 #include <sys/stat.h>
159 #include <sys/syscall.h>
160 #define handle_error(msg) \
162 do { perror(msg); exit(EXIT_FAILURE); } while (0)
163 struct linux_dirent {
165 unsigned long d_ino;
166 off_t d_off;
167 unsigned short d_reclen;
168 char d_name[];
169 };
170 #define BUF_SIZE 1024
172 int
174 main(int argc, char *argv[])
175 {
176 int fd;
177 long nread;
178 char buf[BUF_SIZE];
179 struct linux_dirent *d;
180 char d_type;
181 fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
183 if (fd == -1)
184 handle_error("open");
185 for (;;) {
187 nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
188 if (nread == -1)
189 handle_error("getdents");
190 if (nread == 0)
192 break;
193 printf("--------------- nread=%d ---------------\n", nread);
195 printf("inode# file type d_reclen d_off d_name\n");
196 for (long bpos = 0; bpos < nread;) {
197 d = (struct linux_dirent *) (buf + bpos);
198 printf("%8ld ", d->d_ino);
199 d_type = *(buf + bpos + d->d_reclen - 1);
200 printf("%-10s ", (d_type == DT_REG) ? "regular" :
201 (d_type == DT_DIR) ? "directory" :
202 (d_type == DT_FIFO) ? "FIFO" :
203 (d_type == DT_SOCK) ? "socket" :
204 (d_type == DT_LNK) ? "symlink" :
205 (d_type == DT_BLK) ? "block dev" :
206 (d_type == DT_CHR) ? "char dev" : "???");
207 printf("%4d %10jd %s\n", d->d_reclen,
208 (intmax_t) d->d_off, d->d_name);
209 bpos += d->d_reclen;
210 }
211 }
212 exit(EXIT_SUCCESS);
214 }
215
217 readdir(2), readdir(3), inode(7)
218
220 This page is part of release 5.13 of the Linux man-pages project. A
221 description of the project, information about reporting bugs, and the
222 latest version of this page, can be found at
223 https://www.kernel.org/doc/man-pages/.
224Linux 2021-03-22 GETDENTS(2)