/* @(#)procnameat.c	1.2 11/10/22 Copyright 2011 J. Schilling */
/*
 *	Return a path name for a /proc related access to fd/name if possible.
 *
 *	We need to test this at runtime in order to avoid incorrect behavior
 *	from running a program on a newer OS that it has been compiled for.
 *
 *	NOTE:	The entries /proc/self/{fd|path}/%d are symlinks and thus do
 *		not allow to access paths of unlimited length as possible
 *		with a real openat(fd, name, flags) call.
 *
 *	Copyright (c) 2011 J. Schilling
 */
/*
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * See the file CDDL.Schily.txt in this distribution for details.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file CDDL.Schily.txt from this distribution.
 */

#include <schily/unistd.h>
#include <schily/types.h>
#include <schily/fcntl.h>
#include <schily/maxpath.h>
#include <schily/errno.h>
#include <schily/standard.h>
#include <schily/schily.h>
#include "at-defs.h"

#ifndef	ENAMETOOLONG
#define	ENAMETOOLONG	EINVAL
#endif

#define	PROC_SELF_FD_FORMAT	"/proc/self/fd/%d/%s"	/* Older procfs */
#define	PROC_SELF_PATH_FORMAT	"/proc/self/path/%d/%s"	/* Newer procfs */
#define	PROC_PID_FD_FORMAT	"/proc/%ld/fd/%d/%s"	/* AIX has no self */

char *
proc_fd2name(buf, fd, name)
	char		*buf;
	int		fd;
	const char	*name;
{
static	int	proc_type;

	if (proc_type == 0) {
		int	proc_fd;

		/*
		 * First test the newer feature as the older /proc/self/fd/%d
		 * feature is still available on newer systems.
		 */
		proc_fd = open("/proc/self/path", O_SEARCH);
		if (proc_fd >= 0) {
			proc_type = 1;
			close(proc_fd);
		} else {
			proc_fd = open("/proc/self/fd", O_SEARCH);
			if (proc_fd >= 0) {
				proc_type = 2;
				close(proc_fd);
			} else {
				js_snprintf(buf, PATH_MAX,
					"/proc/%ld/fd", (long)getpid());
				proc_fd = open(buf, O_SEARCH);
				if (proc_fd >= 0) {
					proc_type = 3;
					close(proc_fd);
				} else {
					proc_type = -1;
					return ((char *)0);
				}
			}
		}
	} else if (proc_type < 0) {
		return ((char *)0);
	}
	if (proc_type == 3) {
		if (js_snprintf(buf, PATH_MAX,
				PROC_PID_FD_FORMAT,
				(long)getpid(), fd, name) >= PATH_MAX) {
			seterrno(ENAMETOOLONG);
			return (NULL);
		}
	} else if (js_snprintf(buf, PATH_MAX,
			proc_type == 1 ?
				PROC_SELF_PATH_FORMAT :
				PROC_SELF_FD_FORMAT,
			fd, name) >= PATH_MAX) {
		seterrno(ENAMETOOLONG);
		return (NULL);
	}
	return (buf);
}