.\" Copyright (C) 1995 Andries Brouwer (aeb@cwi.nl) .\" and Copyright 2008, 2015 Michael Kerrisk .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .\" Written 11 June 1995 by Andries Brouwer .\" Modified 22 July 1995 by Michael Chastain : .\" Derived from 'readdir.2'. .\" Modified Tue Oct 22 08:11:14 EDT 1996 by Eric S. Raymond .\" .TH getdents 2 2024-02-25 "Linux man-pages 6.7" .SH NAME getdents, getdents64 \- get directory entries .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .BR "#include " " /* Definition of " SYS_* " constants */" .B #include .P .BI "long syscall(SYS_getdents, unsigned int " fd \ ", struct linux_dirent *" dirp , .BI " unsigned int " count ); .P .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" .B #include .P .BI "ssize_t getdents64(int " fd ", void " dirp [. count "], size_t " count ); .fi .P .IR Note : glibc provides no wrapper for .BR getdents (), necessitating the use of .BR syscall (2). .P .IR Note : There is no definition of .I struct linux_dirent in glibc; see NOTES. .SH DESCRIPTION These are not the interfaces you are interested in. Look at .BR readdir (3) for the POSIX-conforming C library interface. This page documents the bare kernel system call interfaces. .SS getdents() The system call .BR getdents () reads several .I linux_dirent structures from the directory referred to by the open file descriptor .I fd into the buffer pointed to by .IR dirp . The argument .I count specifies the size of that buffer. .P The .I linux_dirent structure is declared as follows: .P .in +4n .EX struct linux_dirent { unsigned long d_ino; /* Inode number */ unsigned long d_off; /* Not an offset; see below */ unsigned short d_reclen; /* Length of this \fIlinux_dirent\fP */ char d_name[]; /* Filename (null\-terminated) */ /* length is actually (d_reclen \- 2 \- offsetof(struct linux_dirent, d_name)) */ /* char pad; // Zero padding byte char d_type; // File type (only since Linux // 2.6.4); offset is (d_reclen \- 1) */ } .EE .in .P .I d_ino is an inode number. .I d_off is a filesystem-specific value with no specific meaning to user space, though on older filesystems it used to be the distance from the start of the directory to the start of the next .IR linux_dirent ; see .BR readdir (3) . .I d_reclen is the size of this entire .IR linux_dirent . .I d_name is a null-terminated filename. .P .I d_type is a byte at the end of the structure that indicates the file type. It contains one of the following values (defined in .IR ): .TP 12 .B DT_BLK This is a block device. .TP .B DT_CHR This is a character device. .TP .B DT_DIR This is a directory. .TP .B DT_FIFO This is a named pipe (FIFO). .TP .B DT_LNK This is a symbolic link. .TP .B DT_REG This is a regular file. .TP .B DT_SOCK This is a UNIX domain socket. .TP .B DT_UNKNOWN The file type is unknown. .P The .I d_type field is implemented since Linux 2.6.4. It occupies a space that was previously a zero-filled padding byte in the .I linux_dirent structure. Thus, on kernels up to and including Linux 2.6.3, attempting to access this field always provides the value 0 .RB ( DT_UNKNOWN ). .P Currently, .\" kernel 2.6.27 .\" The same sentence is in readdir.2 only some filesystems (among them: Btrfs, ext2, ext3, and ext4) have full support for returning the file type in .IR d_type . All applications must properly handle a return of .BR DT_UNKNOWN . .SS getdents64() The original Linux .BR getdents () system call did not handle large filesystems and large file offsets. Consequently, Linux 2.4 added .BR getdents64 (), with wider types for the .I d_ino and .I d_off fields. In addition, .BR getdents64 () supports an explicit .I d_type field. .P The .BR getdents64 () system call is like .BR getdents (), except that its second argument is a pointer to a buffer containing structures of the following type: .P .in +4n .EX struct linux_dirent64 { ino64_t d_ino; /* 64\-bit inode number */ off64_t d_off; /* Not an offset; see getdents() */ unsigned short d_reclen; /* Size of this dirent */ unsigned char d_type; /* File type */ char d_name[]; /* Filename (null\-terminated) */ }; .EE .in .SH RETURN VALUE On success, the number of bytes read is returned. On end of directory, 0 is returned. On error, \-1 is returned, and .I errno is set to indicate the error. .SH ERRORS .TP .B EBADF Invalid file descriptor .IR fd . .TP .B EFAULT Argument points outside the calling process's address space. .TP .B EINVAL Result buffer is too small. .TP .B ENOENT No such directory. .TP .B ENOTDIR File descriptor does not refer to a directory. .SH STANDARDS None. .SH HISTORY SVr4. .\" SVr4 documents additional ENOLINK, EIO error conditions. .TP .BR getdents64 () glibc 2.30. .SH NOTES glibc does not provide a wrapper for .BR getdents (); call .BR getdents () using .BR syscall (2). In that case you will need to define the .I linux_dirent or .I linux_dirent64 structure yourself. .P Probably, you want to use .BR readdir (3) instead of these system calls. .P These calls supersede .BR readdir (2). .SH EXAMPLES .\" FIXME The example program needs to be revised, since it uses the older .\" getdents() system call and the structure with smaller field widths. The program below demonstrates the use of .BR getdents (). The following output shows an example of what we see when running this program on an ext2 directory: .P .in +4n .EX .RB "$" " ./a.out /testfs/" -\-\-\-\-\-\-\-\-\-\-\-\-\-\- nread=120 \-\-\-\-\-\-\-\-\-\-\-\-\-\-\- inode# file type d_reclen d_off d_name 2 directory 16 12 . 2 directory 16 24 .. 11 directory 24 44 lost+found 12 regular 16 56 a 228929 directory 16 68 sub 16353 directory 16 80 sub2 130817 directory 16 4096 sub3 .EE .in .SS Program source \& .\" SRC BEGIN (getdents.c) .EX #define _GNU_SOURCE #include /* Defines DT_* constants */ #include #include #include #include #include #include #include \& struct linux_dirent { unsigned long d_ino; off_t d_off; unsigned short d_reclen; char d_name[]; }; \& #define BUF_SIZE 1024 \& int main(int argc, char *argv[]) { int fd; char d_type; char buf[BUF_SIZE]; long nread; struct linux_dirent *d; \& fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY); if (fd == \-1) err(EXIT_FAILURE, "open"); \& for (;;) { nread = syscall(SYS_getdents, fd, buf, BUF_SIZE); if (nread == \-1) err(EXIT_FAILURE, "getdents"); \& if (nread == 0) break; \& printf("\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- nread=%ld \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\en", nread); printf("inode# file type d_reclen d_off d_name\en"); for (size_t bpos = 0; bpos < nread;) { d = (struct linux_dirent *) (buf + bpos); printf("%8lu ", d\->d_ino); d_type = *(buf + bpos + d\->d_reclen \- 1); printf("%\-10s ", (d_type == DT_REG) ? "regular" : (d_type == DT_DIR) ? "directory" : (d_type == DT_FIFO) ? "FIFO" : (d_type == DT_SOCK) ? "socket" : (d_type == DT_LNK) ? "symlink" : (d_type == DT_BLK) ? "block dev" : (d_type == DT_CHR) ? "char dev" : "???"); printf("%4d %10jd %s\en", d\->d_reclen, (intmax_t) d\->d_off, d\->d_name); bpos += d\->d_reclen; } } \& exit(EXIT_SUCCESS); } .EE .\" SRC END .SH SEE ALSO .BR readdir (2), .BR readdir (3), .BR inode (7)