Make the various findopenbsd() functions non-recursive, eliminating

a global, a couple of parameters, and opening up possibility of
traversing much longer EBR lists without blowing the stack.

Make seach algorithm the same as used in kern/subr_disk.c by checking
all primary partitions in the MBR/EBR before moving to next EBR. This
makes it more likely that everybody finds the same OpenBSD partition.

Largely from a diff posted to tech@ by ucsavl.

2 files changed, 56 insertions, 48 deletions

diff --git a/sys/arch/i386/stand/installboot/installboot.c b/sys/arch/i386/stand/installboot/installboot.c
index be384a635e8..edc4aa6626d 100644
--- a/sys/arch/i386/stand/installboot/installboot.c
+++ b/sys/arch/i386/stand/installboot/installboot.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: installboot.c,v 1.59 2011/03/14 22:14:40 krw Exp $	*/
+/*	$OpenBSD: installboot.c,v 1.60 2011/03/17 12:53:44 krw Exp $	*/
 /*	$NetBSD: installboot.c,v 1.5 1995/11/17 23:23:50 gwr Exp $ */
 
 /*
@@ -103,15 +103,13 @@ static void	devread(int, void *, daddr64_t, size_t, char *);
 static void	sym_set_value(struct sym_data *, char *, u_int32_t);
 static void	pbr_set_symbols(char *, char *, struct sym_data *);
 static void	usage(void);
-static u_int	findopenbsd(int, struct disklabel *, u_int, int *);
+static u_int	findopenbsd(int, struct disklabel *);
 static void	write_bootblocks(int devfd, struct disklabel *);
 
 static int	sr_volume(int, int *, int *);
 static void	sr_installboot(int);
 static void	sr_installpbr(int, int, int);
 
-static u_int	mbr_eoff; /* Offset of the MBR extended partition. */
-
 static void
 usage(void)
 {
@@ -212,9 +210,8 @@ main(int argc, char *argv[])
 void
 write_bootblocks(int devfd, struct disklabel *dl)
 {
-	struct		stat sb;
+	struct stat	sb;
 	u_int		start = 0;
-	int		n = 8;
 
 	/* Write patched proto bootblock(s) into the superblock. */
 	if (fstat(devfd, &sb) < 0)
@@ -234,8 +231,7 @@ write_bootblocks(int devfd, struct disklabel *dl)
 	if (dl->d_type != 0 && dl->d_type != DTYPE_FLOPPY &&
 	    dl->d_type != DTYPE_VND) {
 		/* Find OpenBSD partition. */
-		mbr_eoff = DOSBBSECTOR;	/* Offset of MBR extended partition. */
-		start = findopenbsd(devfd, dl, DOSBBSECTOR, &n);
+		start = findopenbsd(devfd, dl);
 		if (start == (u_int)-1)
  			errx(1, "no OpenBSD partition");
 	}
@@ -251,17 +247,23 @@ write_bootblocks(int devfd, struct disklabel *dl)
 }
 
 u_int
-findopenbsd(int devfd, struct disklabel *dl, u_int mbroff, int *n)
+findopenbsd(int devfd, struct disklabel *dl)
 {
 	struct		dos_mbr mbr;
+	u_int		mbroff = DOSBBSECTOR;
+	u_int		mbr_eoff = DOSBBSECTOR; /* Offset of extended part. */
 	struct		dos_partition *dp;
-	u_int		start = (u_int)-1;
-	int		i;
-
-	/* Limit the number of recursions */
-	if (!(*n)--)
-		return (-1);
+	int		i, maxebr = DOS_MAXEBR, nextebr;
 
+again:
+	if (!maxebr--) {
+		if (verbose)
+			fprintf(stderr, "Traversed more than %d Extended Boot "
+			    "Records (EBRs)\n",
+			    DOS_MAXEBR);
+		return ((u_int)-1);
+	}
+		
 	if (verbose)
 		fprintf(stderr, "%s boot record (%cBR) at sector %u\n",
 		    (mbroff == DOSBBSECTOR) ? "master" : "extended",
@@ -275,6 +277,7 @@ findopenbsd(int devfd, struct disklabel *dl, u_int mbroff, int *n)
 		errx(1, "invalid boot record signature (0x%04X) @ sector %u",
 		    mbr.dmbr_sign, mbroff);
 
+	nextebr = 0;
 	for (i = 0; i < NDOSPART; i++) {
 		dp = &mbr.dmbr_parts[i];
 		if (!dp->dp_size)
@@ -288,24 +291,25 @@ findopenbsd(int devfd, struct disklabel *dl, u_int mbroff, int *n)
 		if (dp->dp_typ == DOSPTYP_OPENBSD) {
 			if (dp->dp_start > (dp->dp_start + mbroff))
 				continue;
-			start = dp->dp_start + mbroff;
-			break;
+			return (dp->dp_start + mbroff);
 		}
 
-		if (dp->dp_typ == DOSPTYP_EXTEND ||
-		    dp->dp_typ == DOSPTYP_EXTENDL) {
-			mbroff = dp->dp_start + mbr_eoff;
+		if (!nextebr && (dp->dp_typ == DOSPTYP_EXTEND ||
+		    dp->dp_typ == DOSPTYP_EXTENDL)) {
+			nextebr = dp->dp_start + mbr_eoff;
+			if (nextebr < dp->dp_start)
+				nextebr = (u_int)-1;
 			if (mbr_eoff == DOSBBSECTOR)
 				mbr_eoff = dp->dp_start;
-			if (mbroff < dp->dp_start)
-				continue;
-			start = findopenbsd(devfd, dl, mbroff, n);
-			if (start != (u_int)-1)
-				break;
 		}
 	}
 
-	return (start);
+	if (nextebr && nextebr != (u_int)-1) {
+		mbroff = nextebr;
+		goto again;
+	}
+
+	return ((u_int)-1);
 }
 
 /*
diff --git a/sys/arch/i386/stand/libsa/biosdev.c b/sys/arch/i386/stand/libsa/biosdev.c
index 0b58f714581..de6efca14e5 100644
--- a/sys/arch/i386/stand/libsa/biosdev.c
+++ b/sys/arch/i386/stand/libsa/biosdev.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: biosdev.c,v 1.82 2011/03/15 14:00:26 krw Exp $	*/
+/*	$OpenBSD: biosdev.c,v 1.83 2011/03/17 12:53:44 krw Exp $	*/
 
 /*
  * Copyright (c) 1996 Michael Shalayeff
@@ -46,12 +46,11 @@ static int biosdisk_errno(u_int);
 int CHS_rw (int, int, int, int, int, int, void *);
 static int EDD_rw (int, int, u_int32_t, u_int32_t, void *);
 
-static u_int findopenbsd(bios_diskinfo_t *, u_int, const char **, int *);
+static u_int findopenbsd(bios_diskinfo_t *, const char **);
 
 extern int debug;
 int bios_bootdev;
 int bios_cddev = -1;		/* Set by srt0 if coming from CD */
-u_int mbr_eoff;			/* Offset of MBR extended partition. */
 
 #if 0
 struct biosdisk {
@@ -350,15 +349,16 @@ biosd_io(int rw, bios_diskinfo_t *bd, u_int off, int nsect, void *buf)
  * Try to read the bsd label on the given BIOS device
  */
 static u_int
-findopenbsd(bios_diskinfo_t *bd, u_int mbroff, const char **err, int *n)
+findopenbsd(bios_diskinfo_t *bd, const char **err)
 {
 	struct dos_mbr mbr;
 	struct dos_partition *dp;
-	u_int start = (u_int)-1;
-	int error, i;
+	u_int mbroff = DOSBBSECTOR;
+	u_int mbr_eoff = DOSBBSECTOR;	/* Offset of MBR extended partition. */
+	int error, i, maxebr = DOS_MAXEBR, nextebr;
 
-	/* Limit the number of recursions */
-	if (!(*n)--) {
+again:
+	if (!maxebr--) {
 		*err = "too many extended partitions";
 		return (-1);
 	}
@@ -378,6 +378,7 @@ findopenbsd(bios_diskinfo_t *bd, u_int mbroff, const char **err, int *n)
 	}
 
 	/* Search for OpenBSD partition */
+	nextebr = 0;
 	for (i = 0; i < NDOSPART; i++) {
 		dp = &mbr.dmbr_parts[i];
 		if (!dp->dp_size)
@@ -393,24 +394,29 @@ findopenbsd(bios_diskinfo_t *bd, u_int mbroff, const char **err, int *n)
 		if (dp->dp_typ == DOSPTYP_OPENBSD) {
 			if (dp->dp_start > (dp->dp_start + mbroff))
 				continue;
-			start = dp->dp_start + mbroff;
-			break;
+			return (dp->dp_start + mbroff);
 		}
 
-		if (dp->dp_typ == DOSPTYP_EXTEND ||
-		    dp->dp_typ == DOSPTYP_EXTENDL) {
-			mbroff = dp->dp_start + mbr_eoff;
+		/*
+		 * Record location of next ebr if and only if this is the first
+		 * extended partition in this boot record!
+		 */
+		if (!nextebr && (dp->dp_typ == DOSPTYP_EXTEND ||
+		    dp->dp_typ == DOSPTYP_EXTENDL)) {
+			nextebr = dp->dp_start + mbr_eoff;
+			if (nextebr < dp->dp_start)
+				nextebr = (u_int)-1;
 			if (mbr_eoff == DOSBBSECTOR)
 				mbr_eoff = dp->dp_start;
-			if (mbroff < dp->dp_start)
-				continue;
-			start = findopenbsd(bd, mbroff, err, n);
-			if (start != (u_int)-1)
-				break;
 		}
 	}
 
-	return (start);
+	if (nextebr && nextebr != (u_int)-1) {
+		mbroff = nextebr;
+		goto again;
+	}
+
+	return (-1);
 }
 
 const char *
@@ -420,7 +426,6 @@ bios_getdisklabel(bios_diskinfo_t *bd, struct disklabel *label)
 	char *buf;
 	const char *err = NULL;
 	int error;
-	int n = 8;
 
 	/* Sanity check */
 	if (bd->bios_edd == -1 &&
@@ -429,8 +434,7 @@ bios_getdisklabel(bios_diskinfo_t *bd, struct disklabel *label)
 
 	/* MBR is a harddisk thing */
 	if (bd->bios_number & 0x80) {
-		mbr_eoff = DOSBBSECTOR;
-		start = findopenbsd(bd, DOSBBSECTOR, &err, &n);
+		start = findopenbsd(bd, &err);
 		if (start == (u_int)-1) {
 			if (err != NULL)
 				return (err);