getdirentries.2

早期freebsd实现

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.\"	@(#)getdirentries.2	8.1 (Berkeley) 6/9/93
.\"
.Dd June 9, 1993
.Dt GETDIRENTRIES 2
.Os
.Sh NAME
.Nm getdirentries
.Nd "get directory entries in a filesystem independent format"
.Sh SYNOPSIS
.Fd #include <sys/dirent.h>
.Ft int
.Fn getdirentries "int fd" "char *buf" "int nbytes" "long *basep"
.Sh DESCRIPTION
.Fn Getdirentries
reads directory entries from the directory
referenced by the file descriptor
.Fa fd
into the buffer pointed to by
.Fa buf ,
in a filesystem independent format.
Up to
.Fa nbytes
of data will be transferred.
.Fa Nbytes
must be greater than or equal to the
block size associated with the file,
see
.Xr stat 2 .
Some filesystems may not support
.Fn getdirentries
with buffers smaller than this size.
.Pp
The data in the buffer is a series of
.Em dirent
structures each containing the following entries:
.Bd -literal -offset indent
unsigned long	d_fileno;
unsigned short	d_reclen;
unsigned short	d_namlen;
char    	d_name[MAXNAMELEN + 1]; /* see below */
.Ed
.Pp
The
.Fa d_fileno
entry is a number which is unique for each
distinct file in the filesystem.
Files that are linked by hard links (see
.Xr link 2 )
have the same
.Fa d_fileno .
The
.Fa d_reclen
entry is the length, in bytes, of the directory record.
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 MAXNAMELEN
\&+ 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 .
A value of zero is returned when
the end of the directory has been reached.
.Pp
.Fn Getdirentries
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 ,
or zero.
.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
.Fn Getdirentries
will fail if:
.Bl -tag -width [EFAULT]
.It EBADF
.Fa fd
is not a valid file descriptor open for reading.
.It EFAULT
Either
.Fa buf
or
.Fa basep
point outside the allocated address space.
.It EIO
An
.Tn I/O
error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr open 2 ,
.Xr lseek 2
.Sh HISTORY
The
.Nm getdirentries
function first appeared in 4.4BSD.