freebsd-src/lib/libsys/getdirentries.2

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.Dd September 5, 2023
.Dt GETDIRENTRIES 2
.Os
.Sh NAME
.Nm getdirentries ,
.Nm getdents
.Nd "get directory entries in a file system independent format"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In dirent.h
.Ft ssize_t
.Fn getdirentries "int fd" "char *buf" "size_t nbytes" "off_t *basep"
.Ft ssize_t
.Fn getdents "int fd" "char *buf" "size_t nbytes"
.Sh DESCRIPTION
The
.Fn getdirentries
and
.Fn getdents
system calls read directory entries from the directory
referenced by the file descriptor
.Fa fd
into the buffer pointed to by
.Fa buf ,
in a file system independent format.
Up to
.Fa nbytes
of data will be transferred.
The
.Fa nbytes
argument must be greater than or equal to the
block size associated with the file,
see
.Xr stat 2 .
Some file systems may not support these system calls
with buffers smaller than this size.
.Pp
The data in the buffer is a series of
.Vt dirent
structures each containing the following entries:
.Bd -literal -offset indent
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 */
.Ed
.Pp
The
.Fa 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
.Xr link 2 )
have the same
.Fa d_fileno .
The
.Fa d_off
field returns a cookie which, if non-zero, can be used with
.Xr lseek 2
to position the directory descriptor to the next entry.
The
.Fa d_reclen
entry is the length, in bytes, of the directory record.
The
.Fa d_type
entry is the type of the file pointed to by the directory record.
The file type values are defined in
.Fa <sys/dirent.h> .
The
.Fa d_name
entry contains a null terminated file name.
The
.Fa d_namlen
entry specifies the length of the file name excluding the null byte.
Thus the actual size of
.Fa d_name
may vary from 1 to
.Dv MAXNAMLEN
\&+ 1.
.Pp
Entries may be separated by extra space.
The
.Fa d_reclen
entry may be used as an offset from the start of a
.Fa dirent
structure to the next structure, if any.
.Pp
The actual number of bytes transferred is returned.
The current position pointer associated with
.Fa fd
is set to point to the next block of entries.
The pointer may not advance by the number of bytes returned by
.Fn getdirentries
or
.Fn getdents .
A value of zero is returned when
the end of the directory has been reached.
.Pp
If the
.Fa basep
pointer value is non-NULL,
the
.Fn getdirentries
system call writes the position of the block read into the location pointed to by
.Fa basep .
Alternatively, the current position pointer may be set and retrieved by
.Xr lseek 2 .
The current position pointer should only be set to a value returned by
.Xr lseek 2 ,
a value returned in the location pointed to by
.Fa basep
.Po Fn getdirentries
only
.Pc ,
a value returned in the
.Fa d_off
field if it is non-zero,
or zero.
.Sh IMPLEMENTATION NOTES
The
.Fa 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
.Xr lseek 2
at this time.
.Sh RETURN VALUES
If successful, the number of bytes actually transferred is returned.
Otherwise, -1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn getdirentries
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument
is not a valid file descriptor open for reading.
.It Bq Er EFAULT
Either
.Fa buf
or non-NULL
.Fa basep
point outside the allocated address space.
.It Bq Er EINVAL
The file referenced by
.Fa fd
is not a directory, or
.Fa nbytes
is too small for returning a directory entry or block of entries,
or the current position pointer is invalid.
.It Bq Er EIO
An
.Tn I/O
error occurred while reading from or writing to the file system.
.It Bq Er EINTEGRITY
Corrupted data was detected while reading from the file system.
.It Bq Er ENOENT
Directory unlinked but still open.
.El
.Sh SEE ALSO
.Xr lseek 2 ,
.Xr open 2 ,
.Xr directory 3 ,
.Xr dir 5
.Sh HISTORY
The
.Fn getdirentries
system call first appeared in
.Bx 4.4 .
The
.Fn getdents
system call first appeared in
.Fx 3.0 .