Use cleanup_fdp to quiet clang-analyzer

This avoids a "dead nested assignment" warning because clang
doesn't understand that we're explicitly setting to -1 for the
cleanup function.

Signed-off-by: Colin Walters <walters@verbum.org>

libcomposefs/lcfs-utils.h

@@ -45,6 +45,9 @@ static inline void cleanup_freep(void *p)
 		free(*pp);
 }
 
+// A wrapper around close() that takes a pointer to a file descriptor (integer):
+// - Never returns an error (and preserves errno)
+// - Sets the value to -1 after closing to make cleanup idempotent
 static inline void cleanup_fdp(int *fdp)
 {
 	PROTECT_ERRNO;
@@ -55,6 +58,7 @@ static inline void cleanup_fdp(int *fdp)
 	fd = *fdp;
 	if (fd != -1)
 		(void)close(fd);
+	*fdp = -1;
 }
 
 #define cleanup_free __attribute__((cleanup(cleanup_freep)))

tools/mkcomposefs.c

@@ -245,8 +245,7 @@ static int copy_file_with_dirs_if_needed(const char *src, const char *dst_base,
 			return res;
 		}
 	}
-	close(sfd);
-	sfd = -1;
+	cleanup_fdp(&sfd);
 
 	/* Make sure file is readable by all */
 	res = fchmod(dfd, 0644);
@@ -258,8 +257,7 @@ static int copy_file_with_dirs_if_needed(const char *src, const char *dst_base,
 	if (res < 0) {
 		return res;
 	}
-	close(dfd);
-	dfd = -1;
+	cleanup_fdp(&dfd);
 
 	if (try_enable_fsverity) {
 		/* Try to enable fsverity */