[PATCH] EDD: read disk80 MBR signature, export through edd module

From: Matt Domsch <Matt_Domsch@dell.com>


There are 4 bytes in the MSDOS master boot record, at offset 0x1b8,
which may contain a per-system-unique signature.  By first writing a unique
signature to each disk in the system, then rebooting, and then reading the
MBR to get the signature for the boot disk (int13 dev 80h), userspace may
use it to compare against disks it knows as named /dev/[hs]d[a-z], and thus
determine which disk is the BIOS boot disk, thus where the /boot, / and
boot loaders should be placed.

This is useful in the case where the BIOS is not EDD3.0 compliant, thus
doesn't provide the PCI bus/dev/fn and IDE/SCSI location of the boot disk,
yet you need to know which disk is the boot disk.  It's most useful in OS
installers.

This patch retrieves the signature from the disk in setup.S, stores it in a
space reserved in the empty_zero_page, copies it somewhere safe in setup.c,
and exports it via /sys/firmware/edd/int13_disk80/mbr_signature in edd.c.
Code is covered under CONFIG_EDD=[ym].

Documentation/i386/zero-page.txt

@@ -72,8 +72,10 @@ Offset	Type		Description
 0x21c	unsigned long	INITRD_SIZE, size in bytes of ramdisk image
 0x220	4 bytes		(setup.S)
 0x224	unsigned short	setup.S heap end pointer
+0x2cc	4 bytes		DISK80_SIG_BUFFER (setup.S)
 0x2d0 - 0x600		E820MAP
-0x600 - 0x7D4		EDDBUF (setup.S)
+0x600 - 0x7ff		EDDBUF (setup.S) for disk signature read sector
+0x600 - 0x7d3		EDDBUF (setup.S) for edd data
 
 0x800	string, 2K max	COMMAND_LINE, the kernel commandline as
 			copied using CL_OFFSET.

arch/i386/boot/setup.S

@@ -49,6 +49,8 @@
  * by Matt Domsch <Matt_Domsch@dell.com> October 2002
  * conformant to T13 Committee www.t13.org
  *   projects 1572D, 1484D, 1386D, 1226DT
+ * disk signature read by Matt Domsch <Matt_Domsch@dell.com>
+ *	and Andrew Wilks <Andrew_Wilks@dell.com> September 2003
  */
 
 #include <linux/config.h>
@@ -578,6 +580,25 @@ done_apm_bios:
 #endif
 
 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
+# Read the first sector of device 80h and store the 4-byte signature
+	movl	$0xFFFFFFFF, %eax
+	movl	%eax, (DISK80_SIG_BUFFER)	# assume failure
+	movb	$READ_SECTORS, %ah
+	movb	$1, %al				# read 1 sector
+	movb	$0x80, %dl			# from device 80
+	movb	$0, %dh				# at head 0
+	movw	$1, %cx				# cylinder 0, sector 0
+	pushw	%es
+	pushw	%ds
+	popw	%es
+	movw	$EDDBUF, %bx
+	int	$0x13
+	jc	disk_sig_done
+	movl	(EDDBUF+MBR_SIG_OFFSET), %eax
+	movl	%eax, (DISK80_SIG_BUFFER)	# store success
+disk_sig_done:
+	popw	%es
+
 # Do the BIOS Enhanced Disk Drive calls
 # This consists of two calls:
 #    int 13h ah=41h "Check Extensions Present"

arch/i386/kernel/edd.c

@@ -2,6 +2,7 @@
  * linux/arch/i386/kernel/edd.c
  *  Copyright (C) 2002, 2003 Dell Inc.
  *  by Matt Domsch <Matt_Domsch@dell.com>
+ *  disk80 signature by Matt Domsch, Andrew Wilks, and Sandeep K. Shandilya
  *
  * BIOS Enhanced Disk Drive Services (EDD)
  * conformant to T13 Committee www.t13.org
@@ -59,9 +60,9 @@ MODULE_AUTHOR("Matt Domsch <Matt_Domsch@Dell.com>");
 MODULE_DESCRIPTION("sysfs interface to BIOS EDD information");
 MODULE_LICENSE("GPL");
 
-#define EDD_VERSION "0.10 2003-Oct-11"
+#define EDD_VERSION "0.12 2004-Jan-26"
 #define EDD_DEVICE_NAME_SIZE 16
-#define REPORT_URL "http://domsch.com/linux/edd30/results.html"
+#define REPORT_URL "http://linux.dell.com/edd/results.html"
 
 #define left (PAGE_SIZE - (p - buf) - 1)
 
@@ -259,6 +260,14 @@ edd_show_version(struct edd_device *edev, char *buf)
 	return (p - buf);
 }
 
+static ssize_t
+edd_show_disk80_sig(struct edd_device *edev, char *buf)
+{
+	char *p = buf;
+	p += snprintf(p, left, "0x%08x\n", edd_disk80_sig);
+	return (p - buf);
+}
+
 static ssize_t
 edd_show_extensions(struct edd_device *edev, char *buf)
 {
@@ -429,6 +438,15 @@ edd_has_edd30(struct edd_device *edev)
 	return 1;
 }
 
+static int
+edd_has_disk80_sig(struct edd_device *edev)
+{
+	struct edd_info *info = edd_dev_get_info(edev);
+	if (!edev || !info)
+		return 0;
+	return info->device == 0x80;
+}
+
 static EDD_DEVICE_ATTR(raw_data, 0444, edd_show_raw_data, NULL);
 static EDD_DEVICE_ATTR(version, 0444, edd_show_version, NULL);
 static EDD_DEVICE_ATTR(extensions, 0444, edd_show_extensions, NULL);
@@ -443,6 +461,7 @@ static EDD_DEVICE_ATTR(default_sectors_per_track, 0444,
 		       edd_has_default_sectors_per_track);
 static EDD_DEVICE_ATTR(interface, 0444, edd_show_interface, edd_has_edd30);
 static EDD_DEVICE_ATTR(host_bus, 0444, edd_show_host_bus, edd_has_edd30);
+static EDD_DEVICE_ATTR(mbr_signature, 0444, edd_show_disk80_sig, edd_has_disk80_sig);
 
 
 /* These are default attributes that are added for every edd
@@ -464,6 +483,7 @@ static struct edd_attribute * edd_attrs[] = {
 	&edd_attr_default_sectors_per_track,
 	&edd_attr_interface,
 	&edd_attr_host_bus,
+	&edd_attr_mbr_signature,
 	NULL,
 };
 

arch/i386/kernel/i386_ksyms.c

@@ -32,7 +32,6 @@
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
 #include <asm/nmi.h>
-#include <asm/edd.h>
 #include <asm/ist.h>
 
 extern void dump_thread(struct pt_regs *, struct user *);
@@ -203,11 +202,6 @@ EXPORT_SYMBOL(kunmap_atomic);
 EXPORT_SYMBOL(kmap_atomic_to_page);
 #endif
 
-#ifdef CONFIG_EDD_MODULE
-EXPORT_SYMBOL(edd);
-EXPORT_SYMBOL(eddnr);
-#endif
-
 #if defined(CONFIG_X86_SPEEDSTEP_SMI) || defined(CONFIG_X86_SPEEDSTEP_SMI_MODULE)
 EXPORT_SYMBOL(ist_info);
 #endif

arch/i386/kernel/setup.c

@@ -444,6 +444,12 @@ static int __init copy_e820_map(struct e820entry * biosmap, int nr_map)
 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
 unsigned char eddnr;
 struct edd_info edd[EDDMAXNR];
+unsigned int edd_disk80_sig;
+#ifdef CONFIG_EDD_MODULE
+EXPORT_SYMBOL(eddnr);
+EXPORT_SYMBOL(edd);
+EXPORT_SYMBOL(edd_disk80_sig);
+#endif
 /**
  * copy_edd() - Copy the BIOS EDD information
  *              from empty_zero_page into a safe place.
@@ -453,6 +459,7 @@ static inline void copy_edd(void)
 {
      eddnr = EDD_NR;
      memcpy(edd, EDD_BUF, sizeof(edd));
+     edd_disk80_sig = DISK80_SIGNATURE;
 }
 #else
 #define copy_edd() do {} while (0)

include/asm-i386/edd.h

 /*
  * linux/include/asm-i386/edd.h
- *  Copyright (C) 2002 Dell Inc.
+ *  Copyright (C) 2002, 2003 Dell Inc.
  *  by Matt Domsch <Matt_Domsch@dell.com>
  *
  * structures and definitions for the int 13h, ax={41,48}h
@@ -41,6 +41,9 @@
 #define EDDMAGIC1 0x55AA
 #define EDDMAGIC2 0xAA55
 
+#define READ_SECTORS 0x02
+#define MBR_SIG_OFFSET 0x1B8
+#define DISK80_SIG_BUFFER 0x2cc
 #ifndef __ASSEMBLY__
 
 #define EDD_EXT_FIXED_DISK_ACCESS           (1 << 0)
@@ -167,6 +170,7 @@ struct edd_info {
 
 extern struct edd_info edd[EDDMAXNR];
 extern unsigned char eddnr;
+extern unsigned int edd_disk80_sig;
 #endif				/*!__ASSEMBLY__ */
 
 #endif				/* _ASM_I386_EDD_H */

include/asm-i386/setup.h

@@ -44,6 +44,7 @@
 #define INITRD_START (*(unsigned long *) (PARAM+0x218))
 #define INITRD_SIZE (*(unsigned long *) (PARAM+0x21c))
 #define EDID_INFO   (*(struct edid_info *) (PARAM+0x440))
+#define DISK80_SIGNATURE (*(unsigned int*) (PARAM+DISK80_SIG_BUFFER))
 #define EDD_NR     (*(unsigned char *) (PARAM+EDDNR))
 #define EDD_BUF     ((struct edd_info *) (PARAM+EDDBUF))
 #define COMMAND_LINE ((char *) (PARAM+2048))