From 61f3dd6d2da5014d29beaebadcfa599d3e5072a9 Mon Sep 17 00:00:00 2001
From: Corinna Vinschen <corinna@vinschen.de>
Date: Tue, 28 Jan 2020 17:40:40 +0100
Subject: [PATCH] Cygwin: path_conv: add PC_SYM_NOFOLLOW_DIR flag

Usually a trailing slash requires to follow an existing symlink,
even with PC_SYM_NOFOLLOW.  The reason is that "foo/" is equivalent
to "foo/." so the symlink is in fact not the last path component,
"." is.  This is default for almost all scenarios.

PC_SYM_NOFOLLOW_DIR now allows the caller to request not to
follow the symlink even if a trailing slash is given.  This can
be used in callers to perform certain functions Linux-compatible.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
---
 winsup/cygwin/path.cc | 27 ++++++++++++++++++++-------
 winsup/cygwin/path.h  |  1 +
 2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
index a00270210..5ebbddf3a 100644
--- a/winsup/cygwin/path.cc
+++ b/winsup/cygwin/path.cc
@@ -1022,20 +1022,33 @@ path_conv::check (const char *src, unsigned opt,
 		 these operations again on the newly derived path. */
 	      else if (symlen > 0)
 		{
-		  if (component == 0 && !need_directory
+		  if (component == 0
 		      && (!(opt & PC_SYM_FOLLOW)
 			  || (is_known_reparse_point ()
 			      && (opt & PC_SYM_NOFOLLOW_REP))))
 		    {
-		      /* last component of path is a symlink. */
-		      set_symlink (symlen);
-		      if (opt & PC_SYM_CONTENTS)
+		      /* Usually a trailing slash requires to follow a symlink,
+			 even with PC_SYM_NOFOLLOW.  The reason is that "foo/"
+			 is equivalent to "foo/." so the symlink is in fact not
+			 the last path component.
+
+			 PC_SYM_NOFOLLOW_DIR is used to indicate that the
+			 last path component is the target symlink and the
+			 trailing slash is supposed to be ignored. */
+		      if (!need_directory || (opt & PC_SYM_NOFOLLOW_DIR))
 			{
-			  strcpy (THIS_path, sym.contents);
+			  /* last component of path is a symlink. */
+			  set_symlink (symlen);
+			  /* make sure not to set errno to ENOTDIR. */
+			  need_directory = 0;
+			  if (opt & PC_SYM_CONTENTS)
+			    {
+			      strcpy (THIS_path, sym.contents);
+			      goto out;
+			    }
+			  add_ext = true;
 			  goto out;
 			}
-		      add_ext = true;
-		      goto out;
 		    }
 		  /* Following a symlink we can't trust the collected
 		     filesystem information any longer. */
diff --git a/winsup/cygwin/path.h b/winsup/cygwin/path.h
index 72f4bda43..7b89b03a7 100644
--- a/winsup/cygwin/path.h
+++ b/winsup/cygwin/path.h
@@ -59,6 +59,7 @@ enum pathconv_arg
   PC_SYM_NOFOLLOW_PROCFD = _BIT (11),	/* allow /proc/PID/fd redirection */
   PC_KEEP_HANDLE	 = _BIT (12),	/* keep handle for later stat calls */
   PC_NO_ACCESS_CHECK	 = _BIT (13),	/* helper flag for error check */
+  PC_SYM_NOFOLLOW_DIR	 = _BIT (14),	/* don't follow a trailing slash */
   PC_DONT_USE		 = _BIT (31)	/* conversion to signed happens. */
 };