Fix to make making a bootable cd possible again.

ow that the image has grown beyond the 1.44M that fits on a floppy.
(previously, the floppy emulation mode was used for cd's.)

the boot cd now uses 'no emulation mode,' where an image is provided on
the cd that is loaded and executed directly. this is the boot monitor.

in order to make this work (the entry point is the same as where the
image is loaded, and the boot monitor needs its a.out header too) and
keep compatability with the same code being used for regular booting, i
prepended 16 bytes that jumps over its header so execution can start
there.

to be able to read the CD (mostly in order to read the boot image),
boot has to use the already present 'extended read' call, but address
the CD using 2k sectors.

boot/boot.c

@@ -122,6 +122,44 @@ char *bios_err(int err)
 	return "Unknown error";
 }
 
+/* CD's are addressed in 2048-byte sectors.
+ * In order to be able to read CD's but maintain the same interface of 512-byte
+ * sector addressing, we check if the device is a CD in readsectors() and if so,
+ * read it into our own buffer first 
+ */
+int readsectors(u32_t bufaddr, u32_t sector, U8_t count)
+{
+#define CDSECTOR_SIZE 2048
+	static char cdbuf[CDSECTOR_SIZE];
+	static i32_t cdbuf_sec = -1;
+	i32_t cdsec;
+
+	if(device != cddevice) {
+		return biosreadsectors(bufaddr, sector, count);
+	}
+
+	while(count > 0) {
+		u32_t offset;
+#define FACTOR (CDSECTOR_SIZE/SECTOR_SIZE)
+		cdsec = sector / FACTOR;
+		offset = (sector % FACTOR) * SECTOR_SIZE;
+		if(cdsec != cdbuf_sec) {
+			int r;
+			if((r=biosreadsectors(mon2abs(cdbuf), cdsec, 1)) != 0) {
+				printf("error %d\n", r);
+				return r;
+			}
+			cdbuf_sec = cdsec;
+		}
+		raw_copy(bufaddr, mon2abs(cdbuf) + offset, SECTOR_SIZE);
+		bufaddr += SECTOR_SIZE;
+		count--;
+		sector++;
+	}
+
+	return 0;
+}
+
 char *unix_err(int err)
 /* Translate the few errors rawfs can give. */
 {
@@ -515,6 +553,12 @@ void initialize(void)
 	}
 #endif
 
+	/* If we were booted from CD, remember what device it was. */
+	if(cdbooted)
+		cddevice = device;
+	else
+		cddevice = 0xff;	/* Invalid. */
+
 	/* Set the new caddr for relocate. */
 	caddr= newaddr;
 
@@ -564,6 +608,14 @@ void initialize(void)
 			readerr(masterpos, r); exit(1);
 		}
 
+		/* If we're a CD, we know what we want. */
+		if(device == cddevice) {
+			p = 1;	/* We know this is the root FS. */
+			lowsec = table[p]->lowsec;
+			bootdev.primary = p;
+			break;	/* Found! */
+		}
+
 		/* See if you can find "lowsec" back. */
 		for (p= 0; p < NR_PARTITIONS; p++) {
 			if (lowsec - table[p]->lowsec < table[p]->size) break;
@@ -590,12 +642,17 @@ void initialize(void)
 		bootdev.primary= p;
 		masterpos= table[p]->lowsec;
 	}
-	strcpy(bootdev.name, "d0p0");
-	bootdev.name[1] += (device - 0x80);
-	bootdev.name[3] += bootdev.primary;
-	if (bootdev.secondary >= 0) {
-		strcat(bootdev.name, "s0");
-		bootdev.name[5] += bootdev.secondary;
+
+	if(device == cddevice) {
+		strcpy(bootdev.name, CDNAME);
+	} else {
+		strcpy(bootdev.name, "d0p0");
+		bootdev.name[1] += (device - 0x80);
+		bootdev.name[3] += bootdev.primary;
+		if (bootdev.secondary >= 0) {
+			strcat(bootdev.name, "s0");
+			bootdev.name[5] += bootdev.secondary;
+		}
 	}
 
 	/* Find out about the video hardware. */
@@ -1087,7 +1144,7 @@ dev_t name2dev(char *name)
 	n= name;
 	if (strncmp(n, "/dev/", 5) == 0) n+= 5;
 
-	if (strcmp(n, "ram") == 0) {
+	if (strcmp(n, "ram") == 0 || strcmp(n, CDNAME) == 0) {
 		dev= DEV_RAM;
 	} else
 	if (n[0] == 'f' && n[1] == 'd' && numeric(n+2)) {
@@ -1879,7 +1936,6 @@ void monitor(void)
 void boot(void)
 /* Load Minix and start it, among other things. */
 {
-
 	/* Initialize tables. */
 	initialize();
 
@@ -1928,8 +1984,7 @@ void main(int argc, char **argv)
 		fatal(bootdev.name);
 
 	/* Check if it is a bootable Minix device. */
-	if (readsectors(mon2abs(bootcode), lowsec, 1) != 0
-		|| memcmp(bootcode, boot_magic, sizeof(boot_magic)) != 0) {
+	if (readsectors(mon2abs(bootcode), lowsec, 1) != 0) {
 		fprintf(stderr, "edparams: %s: not a bootable Minix device\n",
 			bootdev.name);
 		exit(1);