Applied to original from file_cmds-430.140.2

--- xinstall.c.orig	2024-08-20 16:07:42
+++ xinstall.c	2025-08-18 10:03:32
@@ -70,9 +70,9 @@ __used static const char rcsid[] =
 #ifdef __APPLE__
 #include <TargetConditionals.h>
 #include <copyfile.h>
+#include <sys/attr.h>
+#include <sys/clonefile.h>
 #endif	/* __APPLE__ */
-
-#include "pathnames.h"
 
 /* Bootstrap aid - this doesn't exist in most older releases */
 #ifndef MAP_FAILED
@@ -92,6 +92,8 @@ char *suffix = BACKUP_SUFFIX;
 mode_t mode = S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH;
 char *suffix = BACKUP_SUFFIX;
 
+static int	clone __P((const char *, const char *, int, char *, size_t));
+static void	handle_existing_file __P((char *path, struct stat *sbp));
 void	copy __P((int, char *, int, char *, off_t));
 int	compare __P((int, const char *, size_t, int, const char *, size_t));
 int	create_newfile __P((char *, int, struct stat *));
@@ -100,6 +102,7 @@ void	strip __P((char *));
 void	install_dir __P((char *));
 u_long	numeric_id __P((char *, char *));
 void	strip __P((char *));
+static void tempfile_template __P((const char *, char *, size_t));
 int	trymmap __P((int));
 void	usage __P((void));
 
@@ -276,9 +279,10 @@ install(char *from_name, char *to_name,
 {
 	struct stat from_sb, temp_sb, to_sb;
 	struct utimbuf utb;
-	int devnull, files_match, from_fd=0, serrno, target;
-	int tempcopy, temp_fd, to_fd=0;
+	int devnull, files_match, from_fd=-1, serrno, target;
+	int tempcopy, temp_fd=-1, to_fd=-1;
 	char backup[MAXPATHLEN], *p, pathbuf[MAXPATHLEN], tempfile[MAXPATHLEN];
+	const int tryclone = 1;
 
 	files_match = 0;
 
@@ -334,6 +338,20 @@ install(char *from_name, char *to_name,
 	}
 
 	if (!files_match) {
+		int done_clone = 0;
+	    if (tryclone && !devnull && !dostrip) {
+	        if (!tempcopy && target) {
+	            handle_existing_file(to_name, &to_sb);
+	        }
+	        done_clone = (clone(from_name, to_name, tempcopy, tempfile, sizeof(tempfile)) == 0);
+	    }
+	    if (done_clone &&
+	        (((to_fd = open(tempcopy ? tempfile : to_name, O_RDONLY, 0)) < 0)
+	        || (!tempcopy && fstat(to_fd, &to_sb) == -1))) {
+                (void)unlink(tempcopy ? tempfile : to_name);
+                done_clone = 0;
+		}
+		if (!done_clone) {
 		if (tempcopy) {
 			to_fd = create_tempfile(to_name, tempfile,
 			    sizeof(tempfile));
@@ -350,6 +368,7 @@ install(char *from_name, char *to_name,
 		if (!devnull)
 			copy(from_fd, from_name, to_fd,
 			     tempcopy ? tempfile : to_name, from_sb.st_size);
+		} /* !done_clone */
 	}
 
 	if (dostrip) {
@@ -592,11 +611,11 @@ compare(int from_fd, const char *from_name, size_t fro
 }
 
 /*
- * create_tempfile --
- *	create a temporary file based on path and open it
+ * tempfile_template --
+ *	prepare a template filename for use with mktemp/mkstemp.
  */
-int
-create_tempfile(char *path,
+static void
+tempfile_template(const char *path,
 		char *temp,
 		size_t tsize)
 {
@@ -610,7 +629,49 @@ create_tempfile(char *path,
 		p = temp;
 	(void)strncpy(p, "INS@XXXX", &temp[tsize - 1] - p);
 	temp[tsize - 1] = '\0';
+}
+
+/*
+ * create_tempfile --
+ *	create a temporary file based on path and open it
+ */
+int
+create_tempfile(char *path,
+		char *temp,
+		size_t tsize)
+{
+	tempfile_template(path, temp, tsize);
 	return (mkstemp(temp));
+}
+
+/* unlink or move (backup) an existing file */
+static void
+handle_existing_file(char *path, struct stat *sbp)
+{
+    char backup[MAXPATHLEN];
+    /*
+     * Unlink now... avoid ETXTBSY errors later.  Try to turn
+     * off the append/immutable bits -- if we fail, go ahead,
+     * it might work.
+     */
+    if (sbp->st_flags & NOCHANGEBITS)
+        (void)chflags(path, sbp->st_flags & ~NOCHANGEBITS);
+
+    if (dobackup) {
+        if (snprintf(backup, MAXPATHLEN, "%s%s",
+            path, suffix) != strlen(path) + strlen(suffix))
+            errx(EX_OSERR, "%s: backup filename too long",
+                path);
+        (void)snprintf(backup, MAXPATHLEN, "%s%s",
+            path, suffix);
+        if (verbose)
+            (void)printf("install: %s -> %s\n",
+                path, backup);
+        if (rename(path, backup) < 0)
+            err(EX_OSERR, "rename: %s to %s", path, backup);
+    } else {
+        (void)unlink(path);
+    }
 }
 
 /*
@@ -622,31 +683,8 @@ create_newfile(char *path,
 	       int target,
 	       struct stat *sbp)
 {
-	char backup[MAXPATHLEN];
-
 	if (target) {
-		/*
-		 * Unlink now... avoid ETXTBSY errors later.  Try to turn
-		 * off the append/immutable bits -- if we fail, go ahead,
-		 * it might work.
-		 */
-		if (sbp->st_flags & NOCHANGEBITS)
-			(void)chflags(path, sbp->st_flags & ~NOCHANGEBITS);
-
-		if (dobackup) {
-			if (snprintf(backup, MAXPATHLEN, "%s%s",
-			    path, suffix) != strlen(path) + strlen(suffix))
-				errx(EX_OSERR, "%s: backup filename too long",
-				    path);
-			(void)snprintf(backup, MAXPATHLEN, "%s%s",
-			    path, suffix);
-			if (verbose)
-				(void)printf("install: %s -> %s\n",
-				    path, backup);
-			if (rename(path, backup) < 0)
-				err(EX_OSERR, "rename: %s to %s", path, backup);
-		} else
-			(void)unlink(path);
+		handle_existing_file(path, sbp);
 	}
 
 	return (open(path, O_CREAT | O_RDWR | O_TRUNC, S_IRUSR | S_IWUSR));
@@ -736,6 +774,22 @@ copy(int from_fd, char *from_name,
 }
 
 /*
+ * clone --
+ *	create a clone of a file
+ */
+static int
+clone(const char *from_name, const char *to_name,
+      int use_temp, char *temp_name, size_t tsize)
+{
+    if (use_temp) {
+        tempfile_template(to_name, temp_name, tsize);
+        mktemp(temp_name);
+        to_name = temp_name;
+    }
+    return clonefile(from_name, to_name, CLONE_NOOWNERCOPY);
+}
+
+/*
  * strip --
  *	use strip(1) to strip the target file
  */