Make unlink() work for junction points on Windows.

macdice · adunstan · commit fa56aa23fad3 · 2024-11-08T09:45:40.000+10:30
To support harmonization of Windows and Unix code, teach our unlink() wrapper that junction points need to be unlinked with rmdir() on Windows. Tested-by: Andrew Dunstan <andrew@dunslane.net> Discussion: https://postgr.es/m/CA%2BhUKGLfOOeyZpm5ByVcAt7x5Pn-%3DxGRNCvgiUPVVzjFLtnY0w%40mail.gmail.com (cherry picked from commit f357233) Author: Thomas Munro <tmunro@postgresql.org> Author: Alexandra Wang <alexandra.wang.oss@gmail.com>
diff --git a/src/port/dirmod.c b/src/port/dirmod.c
@@ -99,6 +99,32 @@ int
 pgunlink(const char *path)
 {
 	int			loops = 0;
+	struct stat st;
+
+	/*
+	 * This function might be called for a regular file or for a junction
+	 * point (which we use to emulate symlinks).  The latter must be unlinked
+	 * with rmdir() on Windows.  Before we worry about any of that, let's see
+	 * if we can unlink directly, since that's expected to be the most common
+	 * case.
+	 */
+	if (unlink(path) == 0)
+		return 0;
+	if (errno != EACCES)
+		return -1;
+
+	/*
+	 * EACCES is reported for many reasons including unlink() of a junction
+	 * point.  Check if that's the case so we can redirect to rmdir().
+	 *
+	 * Note that by checking only once, we can't cope with a path that changes
+	 * from regular file to junction point underneath us while we're retrying
+	 * due to sharing violations, but that seems unlikely.  We could perhaps
+	 * prevent that by holding a file handle ourselves across the lstat() and
+	 * the retry loop, but that seems like over-engineering for now.
+	 */
+	if (lstat(path, &st) < 0)
+		return -1;
 
 	/*
 	 * We need to loop because even though PostgreSQL uses flags that allow
@@ -107,7 +133,7 @@ pgunlink(const char *path)
 	 * someone else to close the file, as the caller might be holding locks
 	 * and blocking other backends.
 	 */
-	while (unlink(path))
+	while ((S_ISLNK(st.st_mode) ? rmdir(path) : unlink(path)) < 0)
 	{
 		if (errno != EACCES)
 			return -1;
