Subversion Repositories openrisc_2011-10-31

#ifndef _NO_PREAD

/*

FUNCTION

<<pread>>---read a file from specified position

INDEX

        pread

INDEX

        _pread_r

ANSI_SYNOPSIS

        #include <unistd.h>

        ssize_t pread(int <[fd]>, void *<[buf]>, size_t <[n]>, off_t <[off]>);

        ssize_t _pread_r(struct _reent *<[rptr]>, int <[fd]>,

                         void *<[buf]>, size_t <[n]>, off_t <[off]>);

TRAD_SYNOPSIS

        #include <unistd.h>

        ssize_t pread(<[fd]>, <[buf]>, <[n]>, <[off]>)

        int <[fd]>;

        void *<[buf]>;

        size_t <[n]>;

        off_t <[off]>;

        ssize_t _pread_r(<[rptr]>, <[fd]>, <[buf]>, <[n]>, <[off]>)

        struct _reent *<[rptr]>;

        int <[fd]>;

        void *<[buf]>;

        size_t <[n]>;

        off_t <[off]>;

DESCRIPTION

The <<pread>> function is similar to <<read>>.  One difference is that

<<pread>> has an additional parameter <[off]> which is the offset to

position in the file before reading.  The function also differs in that

the file position is unchanged by the function (i.e. the file position

is the same before and after a call to <<pread>>).

The <<_pread_r>> function is the same as <<pread>>, only a reentrant

struct pointer <[rptr]> is provided to preserve reentrancy.

RETURNS

<<pread>> returns the number of bytes read or <<-1>> if failure occurred.

PORTABILITY

<<pread>> is non-ANSI and is specified by the Single Unix Specification.

Supporting OS subroutine required: <<read>>, <<lseek>>.

*/

#include <_ansi.h>

#include <unistd.h>

#include <reent.h>

ssize_t

_DEFUN (_pread_r, (rptr, fd, buf, n, off),

     struct _reent *rptr _AND

     int fd _AND

     _PTR buf _AND

     size_t n _AND

     off_t off)

{

  off_t cur_pos;

  _READ_WRITE_RETURN_TYPE num_read;

  if ((cur_pos = _lseek_r (rptr, fd, 0, SEEK_CUR)) == (off_t)-1)

    return -1;

  if (_lseek_r (rptr, fd, off, SEEK_SET) == (off_t)-1)

    return -1;

  num_read = _read_r (rptr, fd, buf, n);

  if (_lseek_r (rptr, fd, cur_pos, SEEK_SET) == (off_t)-1)

    return -1;

  return (ssize_t)num_read;

}

#ifndef _REENT_ONLY

ssize_t

_DEFUN (pread, (fd, buf, n, off),

     int fd _AND

     _PTR buf _AND

     size_t n _AND

     off_t off)

{

  return _pread_r (_REENT, fd, buf, n, off);

}

#endif /* !_REENT_ONLY  */

#endif /* !_NO_PREAD  */