postgresql/src/include/port/pg_iovec.h

/*-------------------------------------------------------------------------
 *
 * pg_iovec.h
 *	  Header for vectored I/O functions, to use in place of <sys/uio.h>.
 *
 * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/port/pg_iovec.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef PG_IOVEC_H
#define PG_IOVEC_H

#ifndef WIN32

#include <limits.h>
#include <sys/uio.h>

#else

/* POSIX requires at least 16 as a maximum iovcnt. */
#define IOV_MAX 16

/* Define our own POSIX-compatible iovec struct. */
struct iovec
{
	void	   *iov_base;
	size_t		iov_len;
};

#endif

/* Define a reasonable maximum that is safe to use on the stack. */
#define PG_IOV_MAX Min(IOV_MAX, 32)

#if !HAVE_DECL_PREADV
extern ssize_t preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset);
#endif

#if !HAVE_DECL_PWRITEV
extern ssize_t pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset);
#endif

#endif							/* PG_IOVEC_H */