diff: Don't compare a file or directory to itself

While here, stop abusing struct dirent for something we don't even need
to store.

PR:		254455
MFC after:	1 week
Sponsored by:	Klara, Inc.
Reviewed by:	thj, kevans
Differential Revision:	https://reviews.freebsd.org/D55113

usr.bin/diff/diffdir.c

@@ -41,8 +41,6 @@ static void diffit(struct dirent *, char *, size_t, struct dirent *,
 	char *, size_t, int);
 static void print_only(const char *, size_t, const char *);
 
-#define d_status	d_type		/* we need to store status for -l */
-
 struct inode {
 	dev_t dev;
 	ino_t ino;
@@ -258,7 +256,6 @@ diffit(struct dirent *dp, char *path1, size_t plen1, struct dirent *dp2,
 			flags |= D_EMPTY1;
 			memset(&stb1, 0, sizeof(stb1));
 		}
-
 		if (lstat(path2, &stb2) != 0) {
 			if (!Nflag || errno != ENOENT) {
 				warn("%s", path2);
@@ -315,7 +312,6 @@ diffit(struct dirent *dp, char *path1, size_t plen1, struct dirent *dp2,
 			flags |= D_EMPTY1;
 			memset(&stb1, 0, sizeof(stb1));
 		}
-
 		if (stat(path2, &stb2) != 0) {
 			if (!Nflag || errno != ENOENT) {
 				warn("%s", path2);
@@ -328,6 +324,8 @@ diffit(struct dirent *dp, char *path1, size_t plen1, struct dirent *dp2,
 		if (stb1.st_mode == 0)
 			stb1.st_mode = stb2.st_mode;
 	}
+	if (stb1.st_dev == stb2.st_dev && stb1.st_ino == stb2.st_ino)
+		return;
 	if (S_ISDIR(stb1.st_mode) && S_ISDIR(stb2.st_mode)) {
 		if (rflag)
 			diffdir(path1, path2, flags);
@@ -337,12 +335,12 @@ diffit(struct dirent *dp, char *path1, size_t plen1, struct dirent *dp2,
 		return;
 	}
 	if (!S_ISREG(stb1.st_mode) && !S_ISDIR(stb1.st_mode))
-		dp->d_status = D_SKIPPED1;
+		rc = D_SKIPPED1;
 	else if (!S_ISREG(stb2.st_mode) && !S_ISDIR(stb2.st_mode))
-		dp->d_status = D_SKIPPED2;
+		rc = D_SKIPPED2;
 	else
-		dp->d_status = diffreg(path1, path2, flags, 0);
-	print_status(dp->d_status, path1, path2, "");
+		rc = diffreg(path1, path2, flags, 0);
+	print_status(rc, path1, path2, "");
 }
 
 /*

usr.bin/diff/diffreg.c

@@ -372,6 +372,9 @@ diffreg_stone(char *file1, char *file2, int flags, int capsicum)
 		goto closem;
 	}
 
+	if (stb1.st_dev == stb2.st_dev && stb1.st_ino == stb2.st_ino)
+		goto closem;
+
 	if (lflag)
 		pr = start_pr(file1, file2);
 

usr.bin/diff/tests/diff_test.sh

@@ -432,6 +432,24 @@ prleak_body()
 	atf_check diff -Astone -rul a b
 }
 
+same_head()
+{
+	atf_set "descr" "Don't diff a file or directory with itself"
+}
+same_body()
+{
+	local n=256
+	mkdir a
+	for hi in $(jot -w%02x $n 0) ; do
+		mkdir a/$hi
+		for lo in $(jot -w%02x $n 0) ; do
+			echo "$hi$lo" >a/$hi/$lo
+		done
+	done
+	ln -s a b
+	atf_check timeout 1s diff -rqs a b
+}
+
 atf_init_test_cases()
 {
 	atf_add_test_case simple
@@ -462,4 +480,5 @@ atf_init_test_cases()
 	atf_add_test_case bigc
 	atf_add_test_case bigu
 	atf_add_test_case prleak
+	atf_add_test_case same
 }