unix tool for making bootable plan9 disks.

sys/src/cmd/unix/mbrfix.c

@@ -0,0 +1,196 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
+typedef unsigned char uchar;
+typedef unsigned int uint;
+typedef unsigned long long vlong;
+
+
+enum {
+	Sectsz = 0x200,
+	Psectsz = 11,
+	Pclustsc = 13,
+	Presvd = 14,
+	Pnumfat = 16,
+	Pfatsz = 22,
+	Pfatsz32 = 36,
+	Pvolid = 67,
+};
+
+int
+readn(int f, void *av, int n)
+{
+	char *a;
+	int m, t;
+	a = av;
+	t = 0;
+	while(t < n){
+		m = read(f, a+t, n-t);
+		if(m <= 0){
+			if(t == 0)
+				return m;
+			break;
+		}
+		t += m;
+	}
+	return t;
+}
+
+void
+sysfatal(char *fmt, ...)
+{
+	va_list va;
+	va_start(va, fmt);
+	vfprintf(stderr, fmt, va);
+	va_end(va);
+	fprintf(stderr, "\n");
+	exit(1);
+}
+
+void
+readsect(int fd, uint n, void *data)
+{
+	loff_t off;
+
+	off = (loff_t) n * Sectsz;
+	if(llseek(fd, off, SEEK_SET) != off)
+		sysfatal("seek to sector 0x%x failed", n);
+	if(readn(fd, data, Sectsz) != Sectsz)
+		sysfatal("short read: %m");
+}
+
+void
+writesect(int fd, uint n, void *data)
+{
+	loff_t off;
+
+	off = (loff_t) n * Sectsz;
+	if(llseek(fd, off, SEEK_SET) != off)
+		sysfatal("seek to sector 0x%x failed", n);
+	if(write(fd, data, Sectsz) != Sectsz)
+		sysfatal("short write: %m");
+}
+
+uint
+getulong(uchar *s)
+{
+	return s[0] | (s[1] << 8) | (s[2] << 16) | (s[3] << 24);
+}
+
+void
+putulong(uchar *s, uint n)
+{
+	*s++ = n & 0xff;
+	*s++ = (n >> 8) & 0xff;
+	*s++ = (n >> 16) & 0xff;
+	*s++ = (n >> 24) & 0xff;
+}
+
+
+uint
+getushort(uchar *s)
+{
+	return s[0] | (s[1] << 8);
+}
+
+int
+checksig(uchar *s)
+{
+	return s[0x1fe] == 0x55 && s[0x1ff] == 0xaa;
+}
+
+void
+fixpbs(uchar *pbs, uchar *pbs9, uint lba)
+{
+	uint a;
+	uint fatsz, resvd, numfat;
+
+	numfat = pbs[Pnumfat];
+	fatsz = getushort(&pbs[Pfatsz]);
+	if(fatsz == 0)
+		fatsz = getulong(&pbs[Pfatsz32]);
+	resvd = getushort(&pbs[Presvd]);
+
+	a = pbs9[1] + 2;
+	memcpy(pbs, pbs9, 3);
+	memcpy(pbs+a, pbs9+a, Sectsz-a-2);
+	a = lba + numfat * fatsz + resvd;
+	printf("Xroot=%x\n", a);
+	putulong(&pbs[Pvolid], a);
+}
+
+
+int
+main(int argc, char *argv[])
+{
+	int dev, fd, i;
+	uchar mbr9[Sectsz], pbs9[Sectsz];
+	uchar mbr[Sectsz], pbs[Sectsz];
+	uint lba;
+	int part, want;
+	char *mbrfn, *pbsfn, *devfn;
+
+	if(argc < 4)
+		sysfatal("usage: <device> <mbrfile> <pbsfile> [part]");
+	devfn = argv[1];
+	mbrfn = argv[2];
+	pbsfn = argv[3];
+	want = argc >= 5 ? atoi(argv[4]) : -1;
+	part = -1;
+
+	dev = open(devfn, O_RDWR);
+	if(dev < 0)
+		sysfatal("%s: %m", devfn);
+
+	if((fd = open(mbrfn, O_RDONLY)) < 0)
+		sysfatal("%s: %m", mbrfn);
+	if(readn(fd, mbr9, Sectsz) < 3)
+		sysfatal("%s: too short", mbrfn);
+	close(fd);
+
+	fd = open(pbsfn, O_RDONLY);
+	if(fd < 0)
+		sysfatal("%s: %m", pbsfn);
+	if(readn(fd, pbs9, Sectsz) < 3)
+		sysfatal("%s: too short", pbsfn);
+	if(pbs9[0] != 0xeb)
+		sysfatal("first byte of pbs not a short jump");
+	close(fd);
+
+	readsect(dev, 0, mbr);
+	if(!checksig(mbr))
+		sysfatal("sector 0 is missing signature");
+	for(i=0; i<4; i++){
+		if(mbr[0x1be + i*16] == 0x80 && (part == -1 || i == want))
+			part = i;
+	}
+	if(part == -1)
+		sysfatal("no bootable partitions found");
+	if(want != -1 && part != want)
+		sysfatal("partition %d is not bootable", want);
+
+	lba = getulong(&mbr[0x1be + part*16 + 8]);
+	if(lba == 0)
+		sysfatal("partition %d has zero LBA", part);
+
+	readsect(dev, lba, pbs);
+	if(!checksig(pbs))
+		sysfatal("partition %d (LBA=0x%x) is missing signaure", part, lba);
+	if(getushort(&pbs[Psectsz]) != 512)
+		sysfatal("sector size not 512");
+
+	printf("using partition %d, LBA=0x%x\n", part, lba);
+	memcpy(mbr, mbr9, 446);
+	fixpbs(pbs, pbs9, lba);
+	
+	writesect(dev, 0, mbr);
+	writesect(dev, lba, pbs);
+	
+	close(dev);
+	return 0;
+}