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/*
 *	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 the
 *	object, as follows:
 *
 *		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.  This is
 *			a preorder visit -- objects in the directory
 *			are yet to be visited.
 *
 *		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_DP	The object is a directory for which stat and
 *			open for read were both successful.  This is
 *			a postorder visit -- everything in the directory
 *			has already been visited.
 *
 *		FTW_SL	The object is a symbolic link.
 *
 *		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 <errno.h>
#include "ftw.h"

#define NULL 0

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

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

	/* Try to get file status.  If unsuccessful, errno will say why. */
#ifdef	S_IFLNK
	if (lstat (path, &sb) < 0)
#else
	if (stat (path, &sb) < 0)
#endif
		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)
	switch(sb.st_mode & S_IFMT) {
		case S_IFDIR: break;
#ifdef	S_IFLNK
		case S_IFLNK:
			return (*fn) (path, &sb, FTW_SL);
#endif
		default:
			return (*fn) (path, &sb, FTW_F);
	}

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

	/*
	 *	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 == NULL)
		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);
	blen = n + 14 + 2;	/*  nominal size */
	subpath = malloc (blen);
	if (subpath == NULL) {
		closedir(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 ((dirp = readdir(fd)) != NULL) {
		if (dirp->d_ino != 0
		    && strcmp (dirp->d_name, ".") != 0
		    && strcmp (dirp->d_name, "..") != 0) {
			int i;
			char *p, *q;
			long here;

			/* Append the component name to the working path */
			if ((n + dirp->d_namlen + 2) > blen) {
				char *np;
				blen = n + dirp->d_namlen + 2;
				np = malloc(blen);
				if (np == NULL) {
					closedir(fd);
					free(subpath);
					errno = ENOMEM;
					return -1;
				}
				strcpy(np, subpath);
				free(subpath);
				subpath = np;
				component = &subpath[n];
			}
			p = component;
			q = dirp->d_name;
			for (i = 0; i < dirp->d_namlen && *q != '\0'; i++)
				*p++ = *q++;
			*p = '\0';

			/*
			 *	If we are about to exceed our depth,
			 *	remember where we are and close the file.
			 */
			if (depth <= 1) {
				here = telldir(fd);
				closedir(fd);
			}

			/*
			 *	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)
					closedir (fd);
				return rc;
			}

			/*
			 *	If we closed the file, try to reopen it.
			 */
			if (depth <= 1) {
				fd = opendir(path);
				if (fd == NULL) {
					free (subpath);
					return -1;
				}
				seekdir (fd, here);
			}
		}
	}

	/*
	 *	We got out of the subdirectory loop.  The return from the
	 *	final iread is in rl.  Call the user function again at the
	 *	end, clean up, and then check that the final
	 *	iread was successful.  If not, give an error return.
	 */
	free (subpath);
	closedir(fd);

	rc = (*fn) (path, &sb, FTW_DP);
	if (rc != 0)
		return rc;

	return 0;
}

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