Make cp and mv optionally preserve hard links.

libbb/Makefile

@@ -45,7 +45,7 @@ obj-y += ask_confirmation.o chomp.o concat_path_file.o copy_file.o \
 	xgetcwd.o xreadlink.o xregcomp.o interface.o remove_file.o last_char_is.o \
 	copyfd.o vherror_msg.o herror_msg.o herror_msg_and_die.o xgethostbyname.o \
 	dirname.o make_directory.o create_icmp_socket.o u_signal_names.o arith.o \
-	simplify_path.o inet_common.o $(LIBBB_MOBJS) $(LIBBB_AROBJS)
+	simplify_path.o inet_common.o inode_hash.o $(LIBBB_MOBJS) $(LIBBB_AROBJS)
 
 
 # Hand off to toplevel Rules.mak

libbb/copy_file.c

@@ -30,7 +30,7 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include "libbb.h"
+#include "busybox.h"
 
 int copy_file(const char *source, const char *dest, int flags)
 {
@@ -131,6 +131,19 @@ int copy_file(const char *source, const char *dest, int flags)
 		}
 	} else if (S_ISREG(source_stat.st_mode)) {
 		FILE *sfp, *dfp=NULL;
+#ifdef CONFIG_FEATURE_PRESERVE_HARDLINKS
+		char *link_name;
+
+		if (!(flags & FILEUTILS_DEREFERENCE) &&
+				is_in_ino_dev_hashtable(&source_stat, &link_name)) {
+			if (link(link_name, dest) < 0) {
+				perror_msg("unable to link `%s'", dest);
+				return -1;
+			}
+
+			return 0;
+		}
+#endif
 
 		if ((sfp = fopen(source, "r")) == NULL) {
 			perror_msg("unable to open `%s'", source);
@@ -212,12 +225,21 @@ int copy_file(const char *source, const char *dest, int flags)
 			if (lchown(dest, source_stat.st_uid, source_stat.st_gid) < 0)
 				perror_msg("unable to preserve ownership of `%s'", dest);
 #endif
+
+#ifdef CONFIG_FEATURE_PRESERVE_HARDLINKS
+		add_to_ino_dev_hashtable(&source_stat, dest);
+#endif
+
 		return 0;
 	} else {
 		error_msg("internal error: unrecognized file type");
 		return -1;
 	}
 
+#ifdef CONFIG_FEATURE_PRESERVE_HARDLINKS
+	add_to_ino_dev_hashtable(&source_stat, dest);
+#endif
+
 end:
 
 	if (flags & FILEUTILS_PRESERVE_STATUS) {

libbb/inode_hash.c

@@ -29,6 +29,13 @@
 #define HASH_SIZE	311		/* Should be prime */
 #define hash_inode(i)	((i) % HASH_SIZE)
 
+typedef struct ino_dev_hash_bucket_struct {
+  struct ino_dev_hash_bucket_struct *next;
+  ino_t ino;
+  dev_t dev;
+  char name[1];
+} ino_dev_hashtable_bucket_t;
+
 static ino_dev_hashtable_bucket_t *ino_dev_hashtable[HASH_SIZE];
 
 /*