[PATCH] x86: add command line length to boot protocol

Because the command line is increased to 2048 characters after 2.6.21, it's
not possible for boot loaders and userspace tools to determine the length
of the command line the kernel can understand.  The benefit of knowing the
length is that users can be warned if the command line size is too long
which prevents surprise if things don't work after bootup.

This patch updates the boot protocol to contain a field called
"cmdline_size" that contain the length of the command line (excluding the
terminating zero).

The patch also adds missing fields (of protocol version 2.05) to the x86_64
setup code.

Signed-off-by: Bernhard Walle <bwalle@suse.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Alon Bar-Lev <alon.barlev@gmail.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/x86_64/boot/setup.S b/arch/x86_64/boot/setup.S
index 816d04faa2be..4f8851000d7e 100644
--- a/arch/x86_64/boot/setup.S
+++ b/arch/x86_64/boot/setup.S
@@ -51,6 +51,7 @@
 #include <asm/boot.h>
 #include <asm/e820.h>
 #include <asm/page.h>
+#include <asm/setup.h>
 
 /* Signature words to ensure LILO loaded us right */
 #define SIG1    0xAA55
@@ -80,7 +81,7 @@ start:
 # This is the setup header, and it must start at %cs:2 (old 0x9020:2)
 
                 .ascii  "HdrS"          # header signature
-                .word   0x0205          # header version number (>= 0x0105)
+                .word   0x0206          # header version number (>= 0x0105)
                                         # or else old loadlin-1.5 will fail)
 realmode_swtch: .word   0, 0            # default_switch, SETUPSEG
 start_sys_seg:  .word   SYSSEG
@@ -165,6 +166,10 @@ relocatable_kernel:    .byte 0
 pad2:                  .byte 0
 pad3:                  .word 0
 
+cmdline_size:   .long   COMMAND_LINE_SIZE-1     #length of the command line,
+                                                #added with boot protocol
+                                                #version 2.06
+
 trampoline:     call    start_of_setup
                 .align 16
                                         # The offset at this point is 0x240