x86: add extension fields for bootloader type and version

A long ago, in days of yore, it all began with a god named Thor.
There were vikings and boats and some plans for a Linux kernel
header.  Unfortunately, a single 8-bit field was used for bootloader
type and version.  This has generally worked without *too* much pain,
but we're getting close to flat running out of ID fields.

Add extension fields for both type and version.  The type will be
extended if it the old field is 0xE; the version is a simple MSB
extension.

Keep /proc/sys/kernel/bootloader_type containing
(type << 4) + (ver & 0xf) for backwards compatiblity, but also add
/proc/sys/kernel/bootloader_version which contains the full version
number.

[ Impact: new feature to support more bootloaders ]

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 52 insertions, 7 deletions

diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index cf8dfc70a118..8da3a795083f 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -50,10 +50,9 @@ Protocol 2.08:	(Kernel 2.6.26) Added crc32 checksum and ELF format
 Protocol 2.09:  (Kernel 2.6.26) Added a field of 64-bit physical
                 pointer to single linked list of struct setup_data.
 
-Protocol 2.10:  (Kernel 2.6.31) A protocol for relaxed alignment
+Protocol 2.10:  (Kernel 2.6.31) Added a protocol for relaxed alignment
                 beyond the kernel_alignment added, new init_size and
-                pref_address fields.
-
+                pref_address fields.  Added extended boot loader IDs.
 
 **** MEMORY LAYOUT
 
@@ -173,7 +172,8 @@ Offset	Proto	Name		Meaning
 021C/4  2.00+   ramdisk_size    initrd size (set by boot loader)
 0220/4  2.00+   bootsect_kludge DO NOT USE - for bootsect.S use only
 0224/2  2.01+   heap_end_ptr    Free memory after setup end
-0226/2  N/A     pad1            Unused
+0226/1  2.02+(3 ext_loader_ver  Extended boot loader version
+0227/1  2.02+(3 ext_loader_type Extended boot loader ID
 0228/4  2.02+   cmd_line_ptr    32-bit pointer to the kernel command line
 022C/4  2.03+   ramdisk_max     Highest legal initrd address
 0230/4  2.05+   kernel_alignment Physical addr alignment required for kernel
@@ -197,6 +197,8 @@ Offset	Proto	Name		Meaning
     field are unusable, which means the size of a bzImage kernel
     cannot be determined.
 
+(3) Ignored, but safe to set, for boot protocols 2.02-2.09.
+
 If the "HdrS" (0x53726448) magic number is not found at offset 0x202,
 the boot protocol version is "old".  Loading an old kernel, the
 following parameters should be assumed:
@@ -350,18 +352,32 @@ Protocol:	2.00+
   0xTV here, where T is an identifier for the boot loader and V is
   a version number.  Otherwise, enter 0xFF here.
 
+  For boot loader IDs above T = 0xD, write T = 0xE to this field and
+  write the extended ID minus 0x10 to the ext_loader_type field.
+  Similarly, the ext_loader_ver field can be used to provide more than
+  four bits for the bootloader version.
+
+  For example, for T = 0x15, V = 0x234, write:
+
+  type_of_loader  <- 0xE4
+  ext_loader_type <- 0x05
+  ext_loader_ver  <- 0x23
+
   Assigned boot loader ids:
         0  LILO                 (0x00 reserved for pre-2.00 bootloader)
         1  Loadlin
         2  bootsect-loader      (0x20, all other values reserved)
-        3  SYSLINUX
-        4  EtherBoot
+        3  Syslinux
+        4  Etherboot/gPXE
         5  ELILO
         7  GRUB
-        8  U-BOOT
+        8  U-Boot
         9  Xen
         A  Gujin
         B  Qemu
+        C  Arcturus Networks uCbootloader
+        E  Extended             (see ext_loader_type)
+        F  Special              (0xFF = undefined)
 
   Please contact <hpa@zytor.com> if you need a bootloader ID
   value assigned.
@@ -460,6 +476,35 @@ Protocol:	2.01+
   Set this field to the offset (from the beginning of the real-mode
   code) of the end of the setup stack/heap, minus 0x0200.
 
+Field name:     ext_loader_ver
+Type:           write (optional)
+Offset/size:    0x226/1
+Protocol:       2.02+
+
+  This field is used as an extension of the version number in the
+  type_of_loader field.  The total version number is considered to be
+  (type_of_loader & 0x0f) + (ext_loader_ver << 4).
+
+  The use of this field is boot loader specific.  If not written, it
+  is zero.
+
+  Kernels prior to 2.6.31 did not recognize this field, but it is safe
+  to write for protocol version 2.02 or higher.
+
+Field name:     ext_loader_type
+Type:           write (obligatory if (type_of_loader & 0xf0) == 0xe0)
+Offset/size:    0x227/1
+Protocol:       2.02+
+
+  This field is used as an extension of the type number in
+  type_of_loader field.  If the type in type_of_loader is 0xE, then
+  the actual type is (ext_loader_type + 0x10).
+
+  This field is ignored if the type in type_of_loader is not 0xE.
+
+  Kernels prior to 2.6.31 did not recognize this field, but it is safe
+  to write for protocol version 2.02 or higher.
+
 Field name:     cmd_line_ptr
 Type:           write (obligatory)
 Offset/size:    0x228/4