Add a -Z option which zeroes unused blocks. It can be combined with -E,

in which case unused blocks are first zeroed and then erased.

Reviewed by:	mckusick
MFC after:	3 weeks

sbin/fsck_ffs/fsck.h

@@ -74,6 +74,7 @@
 #define	MINBUFS		10	/* minimum number of buffers required */
 #define	MAXBUFS		40	/* maximum space to allocate to buffers */
 #define	INOBUFSIZE	64*1024	/* size of buffer to read inodes in pass1 */
+#define	ZEROBUFSIZE	(dev_bsize * 128) /* size of zero buffer used by -Z */
 
 union dinode {
 	struct ufs1_dinode dp1;
@@ -306,7 +307,8 @@ char	yflag;			/* assume a yes response */
 int	bkgrdflag;		/* use a snapshot to run on an active system */
 int	bflag;			/* location of alternate super block */
 int	debug;			/* output debugging info */
-int	Eflag;			/* zero out empty data blocks */
+int	Eflag;			/* delete empty data blocks */
+int	Zflag;			/* zero empty data blocks */
 int	inoopt;			/* trim out unused inodes */
 char	ckclean;		/* only do work if not cleanly unmounted */
 int	cvtlevel;		/* convert to newer file system format */
@@ -402,6 +404,7 @@ int		blread(int fd, char *buf, ufs2_daddr_t blk, long size);
 void		bufinit(void);
 void		blwrite(int fd, char *buf, ufs2_daddr_t blk, ssize_t size);
 void		blerase(int fd, ufs2_daddr_t blk, long size);
+void		blzero(int fd, ufs2_daddr_t blk, long size);
 void		cacheino(union dinode *dp, ino_t inumber);
 void		catch(int);
 void		catchquit(int);

sbin/fsck_ffs/fsck_ffs.8

@@ -38,7 +38,7 @@
 .Nd file system consistency check and interactive repair
 .Sh SYNOPSIS
 .Nm
-.Op Fl BEFfnpry
+.Op Fl BEFfnpryZ
 .Op Fl b Ar block
 .Op Fl c Ar level
 .Op Fl m Ar mode
@@ -280,6 +280,15 @@ Assume a yes response to all questions asked by
 .Nm ;
 this should be used with great caution as this is a free license
 to continue after essentially unlimited trouble has been encountered.
+.It Fl Z
+Similar to
+.Fl E ,
+but overwrites unused blocks with zeroes.
+If both
+.Fl E
+and
+.Fl Z
+are specified, blocks are first zeroed and then erased.
 .El
 .Pp
 Inconsistencies checked are as follows:

sbin/fsck_ffs/fsutil.c

@@ -618,6 +618,35 @@ blerase(int fd, ufs2_daddr_t blk, long size)
 	return;
 }
 
+void
+blzero(int fd, ufs2_daddr_t blk, long size)
+{
+	static char *zero;
+	off_t offset, len;
+
+	if (fd < 0)
+		return;
+	len = ZEROBUFSIZE;
+	if (zero == NULL) {
+		zero = calloc(len, 1);
+		if (zero == NULL)
+			errx(EEXIT, "cannot allocate buffer pool");
+	}
+	offset = blk * dev_bsize;
+	if (lseek(fd, offset, 0) < 0)
+		rwerror("SEEK BLK", blk);
+	while (size > 0) {
+		if (size > len)
+			size = len;
+		else
+			len = size;
+		if (write(fd, zero, len) != len)
+			rwerror("WRITE BLK", blk);
+		blk += len / dev_bsize;
+		size -= len;
+	}
+}
+
 /*
  * Verify cylinder group's magic number and other parameters.  If the
  * test fails, offer an option to rebuild the whole cylinder group.

sbin/fsck_ffs/main.c

@@ -82,7 +82,7 @@ main(int argc, char *argv[])
 	sync();
 	skipclean = 1;
 	inoopt = 0;
-	while ((ch = getopt(argc, argv, "b:Bc:CdEfFm:npry")) != -1) {
+	while ((ch = getopt(argc, argv, "b:Bc:CdEfFm:npryZ")) != -1) {
 		switch (ch) {
 		case 'b':
 			skipclean = 0;
@@ -147,6 +147,10 @@ main(int argc, char *argv[])
 			nflag = 0;
 			break;
 
+		case 'Z':
+			Zflag++;
+			break;
+
 		default:
 			usage();
 		}

sbin/fsck_ffs/pass5.c

@@ -252,7 +252,7 @@ pass5(void)
 			frags = 0;
 			for (j = 0; j < fs->fs_frag; j++) {
 				if (testbmap(d + j)) {
-					if (Eflag && start != -1) {
+					if ((Eflag || Zflag) && start != -1) {
 						clear_blocks(start, d + j - 1);
 						start = -1;
 					}
@@ -274,7 +274,7 @@ pass5(void)
 				ffs_fragacct(fs, blk, newcg->cg_frsum, 1);
 			}
 		}
-		if (Eflag && start != -1)
+		if ((Eflag || Zflag) && start != -1)
 			clear_blocks(start, d - 1);
 		if (fs->fs_contigsumsize > 0) {
 			int32_t *sump = cg_clustersum(newcg);
@@ -586,6 +586,10 @@ static void clear_blocks(ufs2_daddr_t start, ufs2_daddr_t end)
 
 	if (debug)
 		printf("Zero frags %jd to %jd\n", start, end);
-	blerase(fswritefd, fsbtodb(&sblock, start),
-	    lfragtosize(&sblock, end - start + 1));
+	if (Zflag)
+		blzero(fswritefd, fsbtodb(&sblock, start),
+		    lfragtosize(&sblock, end - start + 1));
+	if (Eflag)
+		blerase(fswritefd, fsbtodb(&sblock, start),
+		    lfragtosize(&sblock, end - start + 1));
 }