int getdents(unsigned int fd, struct linux_dirent *dirp,
unsigned int count);
int getdents64(unsigned int fd, struct linux_dirent64 *dirp,
unsigned int count);
Note: There are no glibc wrappers for these system calls; see NOTES.
The linux_dirent structure is declared as follows:
struct linux_dirent {
unsigned long d_ino; /* Inode number */
unsigned long d_off; /* Offset to next linux_dirent */
unsigned short d_reclen; /* Length of this linux_dirent */
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)
*/
}
d_ino is an inode number. d_off is the distance from the start of the directory to the start of the next linux_dirent. d_reclen is the size of this entire linux_dirent. d_name is a null-terminated filename.
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 <dirent.h>):
The d_type field is implemented since Linux 2.6.4. It occupies a space that was previously a zero-filled padding byte in the linux_dirent structure. Thus, on kernels up to and including 2.6.3, attempting to access this field always provides the value 0 (DT_UNKNOWN).
Currently, only some filesystems (among them: Btrfs, ext2, ext3, and ext4) have full support for returning the file type in d_type. All applications must properly handle a return of DT_UNKNOWN.
The getdents64() system call is like getdents(), except that its second argument is a pointer to a buffer containing structures of the following type:
struct linux_dirent64 {
ino64_t d_ino; /* 64-bit inode number */
off64_t d_off; /* 64-bit offset to next structure */
unsigned short d_reclen; /* Size of this dirent */
unsigned char d_type; /* File type */
char d_name[]; /* Filename (null-terminated) */
};
These calls supersede readdir(2).
$ ./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
#define _GNU_SOURCE #include <dirent.h> /* Defines DT_* constants */ #include <fcntl.h> #include <stdio.h> #include <unistd.h> #include <stdlib.h> #include <sys/stat.h> #include <sys/syscall.h> #define handle_error(msg) \ do { perror(msg); exit(EXIT_FAILURE); } while (0) struct linux_dirent { 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, nread; char buf[BUF_SIZE]; struct linux_dirent *d; int bpos; char d_type; fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY); if (fd == -1) handle_error("open"); for ( ; ; ) { nread = syscall(SYS_getdents, fd, buf, BUF_SIZE); if (nread == -1) handle_error("getdents"); if (nread == 0) break; printf("--------------- nread=%d ---------------\n", nread); printf("inode# file type d_reclen d_off d_name\n"); for (bpos = 0; bpos < nread;) { d = (struct linux_dirent *) (buf + bpos); printf("%8ld ", 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 %10lld %s\n", d->d_reclen, (long long) d->d_off, d->d_name); bpos += d->d_reclen; } } exit(EXIT_SUCCESS); }