Revise r197763 which fixes filesystem corruption when extending

into un-zeroed storage.

The original patch was questioned by Kirk as it forces the filesystem
to do excessive work initialising inodes on first use, and was never
MFC'd.  This change mimics the newfs(8) approach of zeroing two
blocks of inodes for each new cylinder group.

Reviewed by:	mckusick
MFC after:	3 weeks

sbin/growfs/growfs.c

@@ -371,16 +371,16 @@ static void
 initcg(int cylno, time_t utime, int fso, unsigned int Nflag)
 {
 	DBG_FUNC("initcg")
-	static void *iobuf;
+	static caddr_t iobuf;
 	long blkno, start;
 	ufs2_daddr_t i, cbase, dmax;
 	struct ufs1_dinode *dp1;
 	struct csum *cs;
 	uint d, dupper, dlower;
 
-	if (iobuf == NULL && (iobuf = malloc(sblock.fs_bsize)) == NULL) {
+	if (iobuf == NULL && (iobuf = malloc(sblock.fs_bsize * 3)) == NULL)
 		errx(37, "panic: cannot allocate I/O buffer");
-	}
+
 	/*
 	 * Determine block bounds for cylinder group.
 	 * Allow space for super block summary information in first
@@ -396,17 +396,12 @@ initcg(int cylno, time_t utime, int fso, unsigned int Nflag)
 		dupper += howmany(sblock.fs_cssize, sblock.fs_fsize);
 	cs = &fscs[cylno];
 	memset(&acg, 0, sblock.fs_cgsize);
-	/*
-	 * Note that we do not set cg_initediblk at all.
-	 * In this extension of a previous filesystem
-	 * we have no inodes initialized for the cylinder
-	 * group at all. The first access to that cylinder
-	 * group will do the correct initialization.
-	 */
 	acg.cg_time = utime;
 	acg.cg_magic = CG_MAGIC;
 	acg.cg_cgx = cylno;
 	acg.cg_niblk = sblock.fs_ipg;
+	acg.cg_initediblk = sblock.fs_ipg < 2 * INOPB(&sblock) ?
+	    sblock.fs_ipg : 2 * INOPB(&sblock);
 	acg.cg_ndblk = dmax - cbase;
 	if (sblock.fs_contigsumsize > 0)
 		acg.cg_nclusterblks = acg.cg_ndblk / sblock.fs_frag;
@@ -419,6 +414,7 @@ initcg(int cylno, time_t utime, int fso, unsigned int Nflag)
 		acg.cg_time = 0;
 		acg.cg_old_niblk = acg.cg_niblk;
 		acg.cg_niblk = 0;
+		acg.cg_initediblk = 0;
 		acg.cg_old_btotoff = start;
 		acg.cg_old_boff = acg.cg_old_btotoff +
 		    sblock.fs_old_cpg * sizeof(int32_t);
@@ -538,11 +534,14 @@ initcg(int cylno, time_t utime, int fso, unsigned int Nflag)
 	sblock.fs_cstotal.cs_nbfree += acg.cg_cs.cs_nbfree;
 	sblock.fs_cstotal.cs_nifree += acg.cg_cs.cs_nifree;
 	*cs = acg.cg_cs;
+
+	memcpy(iobuf, &acg, sblock.fs_cgsize);
+	memset(iobuf + sblock.fs_cgsize, '\0',
+	    sblock.fs_bsize * 3 - sblock.fs_cgsize);
+
 	wtfs(fsbtodb(&sblock, cgtod(&sblock, cylno)),
-		sblock.fs_bsize, (char *)&acg, fso, Nflag);
-	DBG_DUMP_CG(&sblock,
-	    "new cg",
-	    &acg);
+	    sblock.fs_bsize * 3, iobuf, fso, Nflag);
+	DBG_DUMP_CG(&sblock, "new cg", &acg);
 
 	DBG_LEAVE;
 	return;