1getdents(2) System Calls Manual getdents(2)
2
6 getdents, getdents64 - get directory entries
7
9 Standard C library (libc, -lc)
10
12 #include <sys/syscall.h> /* Definition of SYS_* constants */
13 #include <unistd.h>
14 long syscall(SYS_getdents, unsigned int fd, struct linux_dirent *dirp,
16 unsigned int count);
17 #define _GNU_SOURCE /* See feature_test_macros(7) */
19 #include <dirent.h>
20 ssize_t getdents64(int fd, void dirp[.count], size_t count);
22 Note: glibc provides no wrapper for getdents(), necessitating the use
24 of syscall(2).
25 Note: There is no definition of struct linux_dirent in glibc; see
27 NOTES.
28
30 These are not the interfaces you are interested in. Look at readdir(3)
31 for the POSIX-conforming C library interface. This page documents the
32 bare kernel system call interfaces.
33 getdents()
35 The system call getdents() reads several linux_dirent structures from
36 the directory referred to by the open file descriptor fd into the buf‐
37 fer pointed to by dirp. The argument count specifies the size of that
38 buffer.
39 The linux_dirent structure is declared as follows:
41 struct linux_dirent {
43 unsigned long d_ino; /* Inode number */
44 unsigned long d_off; /* Offset to next linux_dirent */
45 unsigned short d_reclen; /* Length of this linux_dirent */
46 char d_name[]; /* Filename (null-terminated) */
47 /* length is actually (d_reclen - 2 -
48 offsetof(struct linux_dirent, d_name)) */
49 /*
50 char pad; // Zero padding byte
51 char d_type; // File type (only since Linux
52 // 2.6.4); offset is (d_reclen - 1)
53 */
54 }
55 d_ino is an inode number. d_off is the distance from the start of the
57 directory to the start of the next linux_dirent. d_reclen is the size
58 of this entire linux_dirent. d_name is a null-terminated filename.
59 d_type is a byte at the end of the structure that indicates the file
61 type. It contains one of the following values (defined in <dirent.h>):
62 DT_BLK This is a block device.
64 DT_CHR This is a character device.
66 DT_DIR This is a directory.
68 DT_FIFO This is a named pipe (FIFO).
70 DT_LNK This is a symbolic link.
72 DT_REG This is a regular file.
74 DT_SOCK This is a UNIX domain socket.
76 DT_UNKNOWN The file type is unknown.
78 The d_type field is implemented since Linux 2.6.4. It occupies a space
80 that was previously a zero-filled padding byte in the linux_dirent
81 structure. Thus, on kernels up to and including Linux 2.6.3, attempt‐
82 ing to access this field always provides the value 0 (DT_UNKNOWN).
83 Currently, only some filesystems (among them: Btrfs, ext2, ext3, and
85 ext4) have full support for returning the file type in d_type. All ap‐
86 plications must properly handle a return of DT_UNKNOWN.
87 getdents64()
89 The original Linux getdents() system call did not handle large filesys‐
90 tems and large file offsets. Consequently, Linux 2.4 added get‐
91 dents64(), with wider types for the d_ino and d_off fields. In addi‐
92 tion, getdents64() supports an explicit d_type field.
93 The getdents64() system call is like getdents(), except that its second
95 argument is a pointer to a buffer containing structures of the follow‐
96 ing type:
97 struct linux_dirent64 {
99 ino64_t d_ino; /* 64-bit inode number */
100 off64_t d_off; /* 64-bit offset to next structure */
101 unsigned short d_reclen; /* Size of this dirent */
102 unsigned char d_type; /* File type */
103 char d_name[]; /* Filename (null-terminated) */
104 };
105
107 On success, the number of bytes read is returned. On end of directory,
108 0 is returned. On error, -1 is returned, and errno is set to indicate
109 the error.
110
112 EBADF Invalid file descriptor fd.
113 EFAULT Argument points outside the calling process's address space.
115 EINVAL Result buffer is too small.
117 ENOENT No such directory.
119 ENOTDIR
121 File descriptor does not refer to a directory.
122
124 None.
125
127 SVr4.
128 getdents64()
130 glibc 2.30.
131
133 glibc does not provide a wrapper for getdents(); call getdents() using
134 syscall(2). In that case you will need to define the linux_dirent or
135 linux_dirent64 structure yourself.
136 Probably, you want to use readdir(3) instead of these system calls.
138 These calls supersede readdir(2).
140
142 The program below demonstrates the use of getdents(). The following
143 output shows an example of what we see when running this program on an
144 ext2 directory:
145 $ ./a.out /testfs/
147 --------------- nread=120 ---------------
148 inode# file type d_reclen d_off d_name
149 2 directory 16 12 .
150 2 directory 16 24 ..
151 11 directory 24 44 lost+found
152 12 regular 16 56 a
153 228929 directory 16 68 sub
154 16353 directory 16 80 sub2
155 130817 directory 16 4096 sub3
156 Program source
158 #define _GNU_SOURCE
160 #include <dirent.h> /* Defines DT_* constants */
161 #include <err.h>
162 #include <fcntl.h>
163 #include <stdint.h>
164 #include <stdio.h>
165 #include <stdlib.h>
166 #include <sys/syscall.h>
167 #include <unistd.h>
168 struct linux_dirent {
170 unsigned long d_ino;
171 off_t d_off;
172 unsigned short d_reclen;
173 char d_name[];
174 };
175 #define BUF_SIZE 1024
177 int
179 main(int argc, char *argv[])
180 {
181 int fd;
182 char d_type;
183 char buf[BUF_SIZE];
184 long nread;
185 struct linux_dirent *d;
186 fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
188 if (fd == -1)
189 err(EXIT_FAILURE, "open");
190 for (;;) {
192 nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
193 if (nread == -1)
194 err(EXIT_FAILURE, "getdents");
195 if (nread == 0)
197 break;
198 printf("--------------- nread=%ld ---------------\n", nread);
200 printf("inode# file type d_reclen d_off d_name\n");
201 for (size_t bpos = 0; bpos < nread;) {
202 d = (struct linux_dirent *) (buf + bpos);
203 printf("%8lu ", d->d_ino);
204 d_type = *(buf + bpos + d->d_reclen - 1);
205 printf("%-10s ", (d_type == DT_REG) ? "regular" :
206 (d_type == DT_DIR) ? "directory" :
207 (d_type == DT_FIFO) ? "FIFO" :
208 (d_type == DT_SOCK) ? "socket" :
209 (d_type == DT_LNK) ? "symlink" :
210 (d_type == DT_BLK) ? "block dev" :
211 (d_type == DT_CHR) ? "char dev" : "???");
212 printf("%4d %10jd %s\n", d->d_reclen,
213 (intmax_t) d->d_off, d->d_name);
214 bpos += d->d_reclen;
215 }
216 }
217 exit(EXIT_SUCCESS);
219 }
220
222 readdir(2), readdir(3), inode(7)
223Linux man-pages 6.05 2023-05-03 getdents(2)