x86: boot protocol updates

[sfrench/cifs-2.6.git] / Documentation / i386 / boot.txt

diff --git a/Documentation/i386/boot.txt b/Documentation/i386/boot.txt
index fc49b79bc1ab3341b16fe19ea49402f9fd1955e2..2eb16100bb3fef7658799f5f7f4d259be644b537 100644 (file)
--- a/Documentation/i386/boot.txt
+++ b/Documentation/i386/boot.txt
@@ -170,6 +170,8 @@ Offset      Proto   Name            Meaning
 0238/4 2.06+   cmdline_size    Maximum size of the kernel command line
 023C/4 2.07+   hardware_subarch Hardware subarchitecture
 0240/8 2.07+   hardware_subarch_data Subarchitecture-specific data
+0248/4 2.08+   payload_offset  Offset of kernel payload
+024C/4 2.08+   payload_length  Length of kernel payload
 
 (1) For backwards compatibility, if the setup_sects field contains 0, the
     real value is 4.
@@ -512,6 +514,32 @@ Protocol:  2.07+
 
   A pointer to data that is specific to hardware subarch
 
+Field name:    payload_offset
+Type:          read
+Offset/size:   0x248/4
+Protocol:      2.08+
+
+  If non-zero then this field contains the offset from the end of the
+  real-mode code to the payload.
+
+  The payload may be compressed. The format of both the compressed and
+  uncompressed data should be determined using the standard magic
+  numbers. Currently only gzip compressed ELF is used.
+  
+Field name:    payload_length
+Type:          read
+Offset/size:   0x24c/4
+Protocol:      2.08+
+
+  The length of the payload.
+
+**** THE IMAGE CHECKSUM
+
+From boot protocol version 2.08 onwards the CRC-32 is calculated over
+the entire file using the characteristic polynomial 0x04C11DB7 and an
+initial remainder of 0xffffffff.  The checksum is appended to the
+file; therefore the CRC of the file up to the limit specified in the
+syssize field of the header is always 0.
 
 **** THE KERNEL COMMAND LINE