libntfs: add ntfs_mft_usn_dec() and convert all copy-pastes to use them

ChangeLog

@@ -32,8 +32,8 @@ xx/xx/2006 - 1.13.1-WIP
 	- ntfsinfo: dump either a minimal (default) or the entire attribute
 	  header (--verbose) for all attributes types. Also removed a lot of
 	  redundant code and made some formatting corrections.  (Szaka)
-	- libntfs: add ntfs_str2ucs and ntfs_freeucs function, and convert 
-	  copy-pastes to use them.  (Szaka)
+	- libntfs: add ntfs_str2ucs(), ntfs_freeucs() and ntfs_mft_usn_dec()
+	  functions, and convert all copy-pastes to use them.  (Szaka)
 
 27/02/2006 - 1.13.0 - Lots and lots and lots of fixes and enhancements.
 

include/ntfs/mft.h

@@ -111,6 +111,8 @@ extern ntfs_inode *ntfs_mft_record_alloc(ntfs_volume *vol, ntfs_inode *base_ni);
 
 extern int ntfs_mft_record_free(ntfs_volume *vol, ntfs_inode *ni);
 
+extern int ntfs_mft_usn_dec(MFT_RECORD *mrec);
+
 #ifdef NTFS_RICH
 
 #include "bitmap.h"

libntfs/mft.c

@@ -1935,3 +1935,26 @@ int ntfs_mft_add_index(struct ntfs_dir *dir)
 
 #endif /* NTFS_RICH */
 
+/**
+ * ntfs_mft_usn_dec - Decrement USN by one
+ * @mrec:	pointer to an mft record
+ *
+ * On success return 0 and on error return -1 with errno set.
+ */
+int ntfs_mft_usn_dec(MFT_RECORD *mrec)
+{
+	u16 usn, *usnp;
+
+	if (!mrec) {
+		errno = EINVAL;
+		return -1;
+	}
+	usnp = (u16 *)((char *)mrec + le16_to_cpu(mrec->usa_ofs));
+	usn = le16_to_cpup(usnp);
+	if (usn-- <= 1)
+		usn = 0xfffe;
+	*usnp = cpu_to_le16(usn);
+
+	return 0;
+}
+

ntfsprogs/mkntfs.c

@@ -5101,7 +5101,6 @@ static int mkntfs_redirect(struct mkntfs_options *opts2)
 	pos = g_mftmirr_lcn * g_vol->cluster_size;
 	lw = 1;
 	for (i = 0; i < g_rl_mftmirr[0].length * g_vol->cluster_size / g_vol->mft_record_size; i++) {
-		u16 usn, *usnp;
 		m = (MFT_RECORD*)(g_buf + i * g_vol->mft_record_size);
 		/*
 		 * Decrement the usn by one, so it becomes the same as the one
@@ -5109,11 +5108,10 @@ static int mkntfs_redirect(struct mkntfs_options *opts2)
 		 * $MFTMirr to have the exact same byte by byte content as
 		 * $MFT, rather than just equivalent meaning content.
 		 */
-		usnp = (u16*)((char*)m + le16_to_cpu(m->usa_ofs));
-		usn = le16_to_cpup(usnp);
-		if (usn-- <= 1)
-			usn = 0xfffe;
-		*usnp = cpu_to_le16(usn);
+		if (ntfs_mft_usn_dec(m)) {
+			ntfs_log_error("ntfs_mft_usn_dec");
+			goto done;
+		}
 		if (!opts.no_action)
 			lw = ntfs_mst_pwrite(g_vol->dev, pos, 1, g_vol->mft_record_size, g_buf + i * g_vol->mft_record_size);
 		if (lw != 1) {

ntfsprogs/ntfsclone.c

@@ -1125,13 +1125,8 @@ static void wipe_unused_mft(ntfs_inode *ni)
 
 static void mft_record_write_with_same_usn(ntfs_volume *volume, ntfs_inode *ni)
 {
-	u16 usn, *usnp;
-	
-	usnp = (u16 *)((char *)ni->mrec + le16_to_cpu(ni->mrec->usa_ofs));
-	usn = le16_to_cpup(usnp);
-	if (usn-- <= 1)
-		usn = 0xfffe;
-	*usnp = cpu_to_le16(usn);
+	if (ntfs_mft_usn_dec(ni->mrec))
+		perr_exit("ntfs_mft_usn_dec");
 	
 	if (ntfs_mft_record_write(volume, ni->mft_no, ni->mrec))
 		perr_exit("ntfs_mft_record_write");