/* Copyright (C) 2006 by Paolo Giarrusso - modified from glibc' execvp.c.
     Original copyright notice follows:
  
     Copyright (C) 1991,92,1995-99,2002,2004 Free Software Foundation, Inc.
     This file is part of the GNU C Library.
  
     The GNU C Library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Lesser General Public
     License as published by the Free Software Foundation; either
     version 2.1 of the License, or (at your option) any later version.
  
     The GNU C Library is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Lesser General Public License for more details.
  
     You should have received a copy of the GNU Lesser General Public
     License along with the GNU C Library; if not, write to the Free
     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
     02111-1307 USA.  */
  #include <unistd.h>
  
  #include <stdbool.h>
  #include <stdlib.h>
  #include <string.h>
  #include <errno.h>
  #include <limits.h>
  
  #ifndef TEST
  #include <um_malloc.h>
  #else
  #include <stdio.h>
  #define um_kmalloc malloc
  #endif
  #include <os.h>
  
  /* Execute FILE, searching in the `PATH' environment variable if it contains
     no slashes, with arguments ARGV and environment from `environ'.  */
  int execvp_noalloc(char *buf, const char *file, char *const argv[])
  {
  	if (*file == '\0') {
  		return -ENOENT;
  	}
  
  	if (strchr (file, '/') != NULL) {
  		/* Don't search when it contains a slash.  */
  		execv(file, argv);
  	} else {
  		int got_eacces;
  		size_t len, pathlen;
  		char *name, *p;
  		char *path = getenv("PATH");
  		if (path == NULL)
  			path = ":/bin:/usr/bin";
  
  		len = strlen(file) + 1;
  		pathlen = strlen(path);
  		/* Copy the file name at the top.  */
  		name = memcpy(buf + pathlen + 1, file, len);
  		/* And add the slash.  */
  		*--name = '/';
  
  		got_eacces = 0;
  		p = path;
  		do {
  			char *startp;
  
  			path = p;
  			//Let's avoid this GNU extension.
  			//p = strchrnul (path, ':');
  			p = strchr(path, ':');
  			if (!p)
  				p = strchr(path, '\0');
  
  			if (p == path)
  				/* Two adjacent colons, or a colon at the beginning or the end
  				   of `PATH' means to search the current directory.  */
  				startp = name + 1;
  			else
  				startp = memcpy(name - (p - path), path, p - path);
  
  			/* Try to execute this name.  If it works, execv will not return.  */
  			execv(startp, argv);
  
  			/*
  			if (errno == ENOEXEC) {
  			}
  			*/
  
  			switch (errno) {
  				case EACCES:
  					/* Record the we got a `Permission denied' error.  If we end
  					   up finding no executable we can use, we want to diagnose
  					   that we did find one but were denied access.  */
  					got_eacces = 1;
  				case ENOENT:
  				case ESTALE:
  				case ENOTDIR:
  					/* Those errors indicate the file is missing or not executable
  					   by us, in which case we want to just try the next path
  					   directory.  */
  				case ENODEV:
  				case ETIMEDOUT:
  					/* Some strange filesystems like AFS return even
  					   stranger error numbers.  They cannot reasonably mean
  					   anything else so ignore those, too.  */
  				case ENOEXEC:
  					/* We won't go searching for the shell
  					 * if it is not executable - the Linux
  					 * kernel already handles this enough,
  					 * for us. */
  					break;
  
  				default:
  					/* Some other error means we found an executable file, but
  					   something went wrong executing it; return the error to our
  					   caller.  */
  					return -errno;
  			}
  		} while (*p++ != '\0');
  
  		/* We tried every element and none of them worked.  */
  		if (got_eacces)
  			/* At least one failure was due to permissions, so report that
  			   error.  */
  			return -EACCES;
  	}
  
  	/* Return the error from the last attempt (probably ENOENT).  */
  	return -errno;
  }
  #ifdef TEST
  int main(int argc, char**argv)
  {
  	char buf[PATH_MAX];
  	int ret;
  	argc--;
  	if (!argc) {
  		fprintf(stderr, "Not enough arguments
  ");
  		return 1;
  	}
  	argv++;
  	if (ret = execvp_noalloc(buf, argv[0], argv)) {
  		errno = -ret;
  		perror("execvp_noalloc");
  	}
  	return 0;
  }
  #endif