config(8) patch for review for src dir handling

[Ed Maste]

I've attached a patch I'd like to commit to config(8) for the way it
handles get_srcdir.  I'm asking for review since it partially reverts
some changes made in revision 1.42 of usr.sbin/config/main.c and I'd
like to make sure there are no issues there.

Right now config(8) calls realpath("../..", ... to find the src path
to write into the kernel Makefile.  I want to change this to use $PWD
with the last two path components removed, assuming it's the same dir
as ../.. .

I want to put this in because I often build from an amd(8)-mounted src
tree, and realpath produces a path using amd's special temporary mount
directory /.amd_mnt/... instead of the intended /host_mounts/... type of
path and it times out when accessed that way.  Using the logical cwd
means that the generated Makefile references /host_mounts/... and amd
knows the mount is still in use when building.

Comments?

-Ed

Index: main.c
===================================================================
RCS file: /usr/cvs/src/usr.sbin/config/main.c,v
retrieving revision 1.76
diff -p -u -r1.76 main.c
--- main.c	17 May 2007 04:53:52 -0000	1.76
+++ main.c	18 Dec 2007 21:02:32 -0000
@@ -249,9 +249,30 @@ main(int argc, char **argv)
 static void
 get_srcdir(void)
 {
+        char *pwd;
 
 	if (realpath("../..", srcdir) == NULL)
 		errx(2, "Unable to find root of source tree");
+
+	if ((pwd = getenv("PWD")) != NULL && *pwd == '/' &&
+	    (pwd = strdup(pwd))) {
+        	struct stat lg, phy;
+		int i;
+		char *p;
+
+		/* remove last two path components */
+		for (i = 0; i < 2; i++) {
+			if ((p = strrchr(pwd, '/')) == NULL) {
+				free(pwd);
+				return;
+			}
+			*p = '\0';
+		}
+        	if (stat(pwd, &lg) != -1 && stat(srcdir, &phy) != -1 &&
+                    lg.st_dev == phy.st_dev && lg.st_ino == phy.st_ino)
+			strlcpy(srcdir, pwd, MAXPATHLEN);
+		free(pwd);
+	}
 }
 
 static void