From 8ef0e484b6733fa07bfcfde8cd16dd87d4507c89 Mon Sep 17 00:00:00 2001
From: "A. Wilcox" <AWilcox@Wilcox-Tech.com>
Date: Thu, 14 Mar 2019 12:38:01 -0500
Subject: renameat: finish bringing interface to standard behaviour

---
 src/unistd/renameat.c | 56 +++++++++++++++++++++++++++++++++++----------------
 1 file changed, 39 insertions(+), 17 deletions(-)

diff --git a/src/unistd/renameat.c b/src/unistd/renameat.c
index d0f31c21..e2f03d39 100644
--- a/src/unistd/renameat.c
+++ b/src/unistd/renameat.c
@@ -9,12 +9,31 @@
 #include <unistd.h>
 #include "syscall.h"
 
+static inline int test_symlink_dirness(int fd, const char *pathname)
+{
+	struct stat statbuf;
+	if (fstatat(fd, pathname, &statbuf, AT_SYMLINK_NOFOLLOW) == -1) {
+		return 1;
+	}
+	if (S_ISLNK(statbuf.st_mode)) {
+		if (fstatat(fd, pathname, &statbuf, 0) == -1) return 1;
+
+		if (S_ISDIR(statbuf.st_mode)) return 0;
+		else {
+			errno = ENOTDIR;
+			return -1;
+		}
+	}
+	return 1;
+}
+
 int renameat(int oldfd, const char *old, int newfd, const char *new)
 {
 	char old_copy[PATH_MAX+1], new_copy[PATH_MAX+1];
 	char *base;
 	size_t old_size, new_size;
-	struct stat statbuf;
+	struct stat oldstat, newstat;
+	int r;
 
 	if ((old_size = strlen(old)) > PATH_MAX || \
 	    (new_size = strlen(new)) > PATH_MAX) {
@@ -22,11 +41,18 @@ int renameat(int oldfd, const char *old, int newfd, const char *new)
 		return -1;
 	}
 
-	if (strlen(old) == 0 || strlen(new) == 0) {
+	if (old_size == 0 || new_size == 0) {
 		errno = ENOENT;
 		return -1;
 	}
 
+	/* Test equality of old and new.
+	   If they both resolve to the same dentry, we do nothing. */
+	if (fstatat(oldfd, old, &oldstat, 0) == 0 && \
+	    fstatat(newfd, new, &newstat, 0) == 0 && \
+	    oldstat.st_dev == newstat.st_dev && \
+	    oldstat.st_ino == newstat.st_ino) return 0;
+
 	strcpy(old_copy, old);
 	strcpy(new_copy, new);
 
@@ -50,21 +76,17 @@ int renameat(int oldfd, const char *old, int newfd, const char *new)
 		   of the symlink itself. */
 		strcpy(old_copy, old);
 		old_copy[old_size - 1] = '\0';
-		if (fstatat(oldfd, old_copy, &statbuf, AT_SYMLINK_NOFOLLOW) == -1) {
-			return -1;
-		}
-		if (S_ISLNK(statbuf.st_mode)) {
-			if (fstatat(oldfd, old, &statbuf, 0) == -1) {
-				return -1;
-			}
-			if (S_ISDIR(statbuf.st_mode)) {
-				old = old_copy;
-			} else {
-				/* may as well not waste the syscall */
-				errno = ENOTDIR;
-				return -1;
-			}
-		}
+		r = test_symlink_dirness(oldfd, old_copy);
+		if (r == 0) old = old_copy;
+		else if (r == -1) return -1;
+	}
+
+	if (new[new_size - 1] == '/') {
+		strcpy(new_copy, new);
+		new_copy[new_size - 1] = '\0';
+		r = test_symlink_dirness(newfd, new_copy);
+		if (r == 0) new = new_copy;
+		else if (r == -1) return -1;
 	}
 
 	return syscall(SYS_renameat, oldfd, old, newfd, new);
-- 
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