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getdirentries, getdents – get directory entries in a file system independent format



Standard C Library (libc, -lc)


#include <sys/types.h>
#include <dirent.h>

getdirentries(int fd, char *buf, size_t nbytes, off_t *basep);

getdents(int fd, char *buf, size_t nbytes);


The getdirentries() and getdents() system calls read directory entries from the directory referenced by the file descriptor fd into the buffer pointed to by buf, in a file system independent format. Up to nbytes of data will be transferred. The nbytes argument must be greater than or equal to the block size associated with the file, see stat(2). Some file systems may not support these system calls with buffers smaller than this size.

The data in the buffer is a series of dirent structures each containing the following entries:

ino_t   d_fileno;
off_t   d_off;
uint16_t        d_reclen;
uint8_t d_type;
uint16_t        d_namlen;
char    d_name[MAXNAMLEN + 1];  /* see below */

The d_fileno entry is a number which is unique for each distinct file in the file system. Files that are linked by hard links (see link(2)) have the same d_fileno. The d_off field returns a cookie which, if non-zero, can be used with lseek(2) to position the directory descriptor to the next entry. The d_reclen entry is the length, in bytes, of the directory record. The d_type entry is the type of the file pointed to by the directory record. The file type values are defined in <sys/dirent.h>. The d_name entry contains a null terminated file name. The d_namlen entry specifies the length of the file name excluding the null byte. Thus the actual size of d_name may vary from 1 to MAXNAMLEN amp;+ 1.

Entries may be separated by extra space. The d_reclen entry may be used as an offset from the start of a dirent structure to the next structure, if any.

The actual number of bytes transferred is returned. The current position pointer associated with fd is set to point to the next block of entries. The pointer may not advance by the number of bytes returned by getdirentries() or getdents(). A value of zero is returned when the end of the directory has been reached.

If the basep pointer value is non-NULL , the getdirentries() system call writes the position of the block read into the location pointed to by basep. Alternatively, the current position pointer may be set and retrieved by lseek(2). The current position pointer should only be set to a value returned by lseek(2), a value returned in the location pointed to by basep (getdirentries() only ), a value returned in the d_off field if it is non-zero, or zero.


The d_off field is currently set to 0 by the NFS client, since the directory offset cookies returned by an NFS server cannot be used by lseek(2) at this time.


If successful, the number of bytes actually transferred is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error.


The getdirentries() system call will fail if:
  The fd argument is not a valid file descriptor open for reading.
  Either buf or non-NULL basep point outside the allocated address space.
  The file referenced by fd is not a directory, or nbytes is too small for returning a directory entry or block of entries, or the current position pointer is invalid.
[EIO] An I/O error occurred while reading from or writing to the file system.
  Corrupted data was detected while reading from the file system.


lseek(2), open(2)


The getdirentries() system call first appeared in BSD 4.4 . The getdents() system call first appeared in FreeBSD 3.0 .

GETDIRENTRIES (2) February 14, 2021

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