getdirentries

GETDIRENTRIES(2)            BSD System Calls Manual           GETDIRENTRIES(2)

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

LIBRARY
     Standard C Library (libc, -lc)

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

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

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

DESCRIPTION
     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 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 + 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,
     or zero.

IMPLEMENTATION NOTES
     The d_off field is being used as a cookie to readdir for nfs servers.
     These cookies can be cached and allow to read directory entries at a
     specific offset on demand.

RETURN VALUES
     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.

ERRORS
     The getdirentries() system call will fail if:

     [EBADF]            The fd argument is not a valid file descriptor open
                        for reading.

     [EFAULT]           Either buf or non-NULL basep point outside the
                        allocated address space.

     [EINVAL]           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.

SEE ALSO
     lseek(2), open(2)

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

BSD                              Nov 14, 2018                              BSD