[BusyBox] [PATCH] Add -b and -S flags to ln.c.

[Matthew S. Wood]

Hello,

The following patch adds support for the -S and -b flags to `ln'.  These flags [especially -b] are used extensively in Debian pre and post installation scripts.

Regards,

Matt
-------------- next part --------------
--- ./coreutils/ln.c.orig	2005-04-15 17:00:38.000000000 -0600
+++ ./coreutils/ln.c	2005-04-15 17:01:52.000000000 -0600
@@ -21,21 +21,31 @@
  */
 
 /* BB_AUDIT SUSv3 compliant */
-/* BB_AUDIT GNU options missing: -b, -d, -F, -i, -S, and -v. */
+/* BB_AUDIT GNU options missing: -d, -F, -i, and -v. */
 /* http://www.opengroup.org/onlinepubs/007904975/utilities/ln.html */
 
-/* Mar 16, 2003      Manuel Novoa III   (mjn3 at codepoet.org)
+/* Apr 15, 2004      Matthew S. Wood    (mwood at realmsys.com)
+ *
+ * Implement '-b' (backup) flag.
+ * Implement '-S' (backup suffix) flag.
+ *
+ *
+ * Mar 16, 2003      Manuel Novoa III   (mjn3 at codepoet.org)
  *
  * Fixed bug involving -n option.  Essentially, -n was always in effect.
  */
 
+#include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <errno.h>
 #include "busybox.h"
 
 #define LN_SYMLINK          1
 #define LN_FORCE            2
 #define LN_NODEREFERENCE    4
+#define LN_BACKUP           8
+#define LN_SUFFIX           16
 
 extern int ln_main(int argc, char **argv)
 {
@@ -44,10 +54,11 @@
 	char *last;
 	char *src_name;
 	char *src;
+	char *suffix = "~";
 	struct stat statbuf;
 	int (*link_func)(const char *, const char *);
 
-	flag = bb_getopt_ulflags(argc, argv, "sfn");
+	flag = bb_getopt_ulflags(argc, argv, "sfnbS:", &suffix);
 
 	if (argc == optind) {
 		bb_show_usage();
@@ -80,7 +91,22 @@
 			continue;
 		}
 
-		if (flag & LN_FORCE) {
+		if (flag & LN_BACKUP) {
+				int backup_len = strlen(src) + strlen(suffix) + 2;
+				char *backup = xmalloc(backup_len);
+				snprintf(backup, backup_len, "%s%s", src, suffix);
+				if (rename(src, backup) < 0 && errno != ENOENT) {
+						bb_perror_msg(src);
+						status = EXIT_FAILURE;
+						break;
+				}
+				/*
+				 * When the source and dest are both hard links, a rename
+				 * may succeed even though nothing happened.  Therefore,
+				 * always unlink().
+				 */
+				unlink(src);
+		} else if (flag & LN_FORCE) {
 			unlink(src);
 		}
 
--- ./include/usage.h.orig	2005-04-15 17:00:15.000000000 -0600
+++ ./include/usage.h	2005-04-15 16:54:47.000000000 -0600
@@ -1415,7 +1415,9 @@
 	"Options:\n" \
 	"\t-s\tmake symbolic links instead of hard links\n" \
 	"\t-f\tremove existing destination files\n" \
-	"\t-n\tno dereference symlinks - treat like normal file"
+	"\t-n\tno dereference symlinks - treat like normal file\n" \
+	"\t-b\tmake a backup of the target (if exists) before link operation\n" \
+	"\t-S suffix\tuse suffix instead of ~ when making backup files"
 #define ln_example_usage \
 	"$ ln -s BusyBox /tmp/ls\n" \
 	"$ ls -l /tmp/ls\n" \