/*	@(#)ftw.c	2.1 	*/
/*LINTLIBRARY*/
/***************************************************************
 *	ftw - file tree walk
 *
 *	int ftw (path, fn, depth)  char *path; int (*fn)(); int depth;
 *
 *	Given a path name, ftw starts from the file given by that path
 *	name and visits each file and directory in the tree beneath
 *	that file.  If a single file has multiple links within the
 *	structure, it will be visited once for each such link.
 *	For each object visited, fn is called with three arguments.
 *	The first contains the path name of the object, the second
 *	contains a pointer to a stat buffer which will usually hold
 *	appropriate information for the object and the third will
 *	contain an integer value giving additional information about
 *
 *		FTW_F	The object is a file for which stat was
 *			successful.  It does not guarantee that the
 *			file can actually be read.
 *
 *		FTW_D	The object is a directory for which stat and
 *			open for read were both successful.
 *
 *		FTW_DNR	The object is a directory for which stat
 *			succeeded, but which cannot be read.  Because
 *			the directory cannot be read, fn will not be
 *			called for any descendants of this directory.
 *
 *		FTW_NS	Stat failed on the object because of lack of
 *			appropriate permission.  This indication will
 *			be given, for example, for each file in a
 *			directory with read but no execute permission.
 *			Because stat failed, it is not possible to
 *			determine whether this object is a file or a
 *			directory.  The stat buffer passed to fn will
 *			contain garbage.  Stat failure for any reason
 *			other than lack of permission will be
 *			considered an error and will cause ftw to stop 
 *			and return -1 to its caller.
 *
 *	If fn returns nonzero, ftw stops and returns the same value
 *	to its caller.  If ftw gets into other trouble along the way,
 *	it returns -1 and leaves an indication of the cause in errno.
 *
 *	The third argument to ftw does not limit the depth to which
 *	ftw will go.  Rather, it limits the depth to which ftw will
 *	go before it starts recycling file descriptors.  In general,
 *	it is necessary to use a file descriptor for each level of the
 *	tree, but they can be recycled for deep trees by saving the
 *	position, closing, re-opening, and seeking.  It is possible
 *	to start recycling file descriptors by sensing when we have
 *	run out, but in general this will not be terribly useful if
 *	fn expects to be able to open files.  We could also figure out
 *	how many file descriptors are available and guarantee a certain
 *	number to fn, but we would not know how many to guarantee,
 *	and we do not want to impose the extra overhead on a caller who
 *	knows how many are available without having to figure it out.
 *
 *	It is possible for ftw to die with a memory fault in the event
 *	of a file system so deeply nested that the stack overflows.
 **************************************************************/

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/dir.h>
#include <errno.h>
#include <ftw.h>

#define NULL 0

extern char *malloc(), *strcpy();
extern long lseek();
extern int errno;

int
ftw(path, fn, depth)
char *path;
int (*fn)();
int depth;
{
	int rc, rl, n, fd;
	char *subpath, *component;
	struct stat sb;
	struct direct dir;

	/* Try to get file status.
				If unsuccessful, errno will say why. */
	if(stat(path, &sb) < 0)
		return(errno == EACCES? (*fn)(path, &sb, FTW_NS): -1);

	/*
	 *	The stat succeeded, so we know the object exists.
	 *	If not a directory, call the user function and return.
	 */
	if((sb.st_mode & S_IFMT) != S_IFDIR)
		return((*fn)(path, &sb, FTW_F));

	/*
	 *	The object was a directory.
	 *
	 *	Open a file to read the directory
	 */
	fd = open(path, 0);

	/*
	 *	Call the user function, telling it whether
	 *	the directory can be read.  If it can't be read
	 *	call the user function or indicate an error,
	 *	depending on the reason it couldn't be read.
	 */
	if(fd < 0)
		return(errno == EACCES? (*fn)(path, &sb, FTW_DNR): -1);

	/* We could read the directory.  Call user function. */
	rc = (*fn)(path, &sb, FTW_D);
	if(rc != 0)
		return(rc);

	/* Allocate a buffer to hold generated pathnames. */
	n = strlen(path);
	subpath = malloc((unsigned)(n+DIRSIZ+2));
	if(subpath == NULL) {
		(void)close(fd);
		errno = ENOMEM;
		return(-1);
	}
	
	/* Create a prefix to which we will append component names */
	(void)strcpy(subpath, path);
	if(subpath[0] != '\0' && subpath[n-1] != '/')
		subpath[n++] = '/';
	component = &subpath[n];

	/*
	 *	Read the directory one component at a time.
	 *	We must ignore "." and "..", but other than that,
	 *	just create a path name and call self to check it out.
	 */
	while((rl = read(fd, (char*)&dir, sizeof(struct direct))) ==
					sizeof(struct direct)) {
		if(dir.d_ino != 0 && strcmp(dir.d_name, ".") != 0 &&
				strcmp(dir.d_name, "..") != 0) {
			int i;
			char *p, *q;
			long here;

			/* Append component name to the working path */
			p = component;
			q = dir.d_name;
			for(i=0; i < DIRSIZ && *q != '\0'; i++)
				*p++ = *q++;
			*p = '\0';

			/*
			 *	If we are about to exceed our depth,
			 *	remember where we are and close a file.
			 */
			if(depth <= 1) {
				here = lseek(fd, 0L, 1);
				if(close(fd) < 0) {
					free(subpath);
					return(-1);
				}
			}

			/*
			 *	Do a recursive call to process the file.
			 *	(watch this, sports fans)
			 */
			rc = ftw(subpath, fn, depth-1);
			if(rc != 0) {
				free(subpath);
				if(depth > 1)
					(void)close(fd);
				return(rc);
			}

			/*
			 *	If we closed the file, try to reopen it.
			 */
			if(depth <= 1) {
				fd = open(path, 0);
				if(fd < 0) {
					free(subpath);
					return(-1);
				}
				if(lseek(fd, here, 0) < 0) {
					(void)close(fd);
					free(subpath);
					return(-1);
				}
			}
		}
	}

	/*
	 *	We got out of the subdirectory loop.  The return from
	 *	the final read is in rl.  Clean up and then check if
	 *	the final read was successful.  If not, give an
	 *	error return.
	 */
	free(subpath);
	if(close(fd) < 0 || rl != 0)
		return(-1);
	return(0);
}
