Don't strip off the last slash in the pathname "/". cp used to

stat the pathname "" in order to decide that the pathname "/" is
a directory.  This caused `cp kernel /' to fail if the kernel has
the POSIX behaviour of not allowing the pathname "" to be an alias
for ".".  It presumably also caused `cp /etc/motd /' to fail in
the unlikely event that "." is not stat'able.

Be more careful about concatenating pathnames: don't check that
the pathname fits until prefixes have been discarded (the check
was too strict).  Print the final pathname in error messages.
Terminate the target directory name properly for error messages.
Don't add a slash between components if there is already a slash.

bin/cp/cp.c

@@ -33,7 +33,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	$Id$
+ *	$Id: cp.c,v 1.2 1994/09/24 02:53:41 davidg Exp $
  */
 
 #ifndef lint
@@ -79,7 +79,7 @@ static char sccsid[] = "@(#)cp.c	8.2 (Berkeley) 4/1/94";
 #include "extern.h"
 
 #define	STRIP_TRAILING_SLASH(p) {					\
-        while ((p).p_end > (p).p_path && (p).p_end[-1] == '/')		\
+        while ((p).p_end > (p).p_path + 1 && (p).p_end[-1] == '/')	\
                 *--(p).p_end = 0;					\
 }
 
@@ -253,7 +253,7 @@ copy(argv, type, fts_options)
 	FTS *ftsp;
 	FTSENT *curr;
 	int base, dne, nlen, rval;
-	char *p;
+	char *p, *target_mid;
 
 	if ((ftsp = fts_open(argv, fts_options, mastercmp)) == NULL)
 		err(1, NULL);
@@ -278,14 +278,6 @@ copy(argv, type, fts_options)
                  * source name to the target name.  
                  */
 		if (type != FILE_TO_FILE) {
-			if ((curr->fts_namelen +
-			    to.target_end - to.p_path + 1) > MAXPATHLEN) {
-				warnx("%s/%s: name too long (not copied)", 
-				    to.p_path, curr->fts_name);
-				rval = 1;
-				continue;
-			}
-
 			/*
 			 * Need to remember the roots of traversals to create
 			 * correct pathnames.  If there's a directory being
@@ -317,15 +309,20 @@ copy(argv, type, fts_options)
 				} else
 					base = curr->fts_pathlen;
 
-			if (to.target_end[-1] != '/') {
-				*to.target_end = '/';
-				*(to.target_end + 1) = 0;
-			}
 			p = &curr->fts_path[base];
 			nlen = curr->fts_pathlen - base;
-
-			(void)strncat(to.target_end + 1, p, nlen);
-			to.p_end = to.target_end + nlen + 1;
+			target_mid = to.target_end;
+			if (*p != '/' && target_mid[-1] != '/')
+				*target_mid++ = '/';
+			*target_mid = 0;
+			if (target_mid - to.p_path + nlen > MAXPATHLEN) {
+				warnx("%s%s: name too long (not copied)", 
+				    to.p_path, p);
+				rval = 1;
+				continue;
+			}
+			(void)strncat(target_mid, p, nlen);
+			to.p_end = target_mid + nlen;
 			*to.p_end = 0;
 			STRIP_TRAILING_SLASH(to);
 		}