[bzimage] Report exact initrd length via bzImage header

iPXE currently pads initrd images to a multiple of 4kB and inserts
zero padding between images, as required by some versions of the Linux
kernel.  The overall length reported via the ramdisk_size field in the
bzImage header includes this zero padding.

This causes problems when using memdisk to load a gzip-compressed disk
image.  memdisk treats the ramdisk_size field as containing the exact
length of the initrd image, and uses this length to locate the 8-byte
gzip footer.  This will generally cause memdisk to fail to decompress
the disk image.

Fix by reporting the exact length of the initrd image set, including
any padding inserted between images but excluding any padding added at
the end of the final image.

Reported-by: Levente LEVAI <levail@aviatronic.hu>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/image/bzimage.c

 	}
 }
 
+/**
+ * Align initrd length
+ *
+ * @v len		Length
+ * @ret len		Length rounded up to INITRD_ALIGN
+ */
+static inline size_t bzimage_align ( size_t len ) {
+
+	return ( ( len + INITRD_ALIGN - 1 ) & ~( INITRD_ALIGN - 1 ) );
+}
+
 /**
  * Load initrd
  *
  * @v image		bzImage image
  * @v initrd		initrd image
  * @v address		Address at which to load, or UNULL
- * @ret len		Length of loaded image, rounded up to INITRD_ALIGN
+ * @ret len		Length of loaded image, excluding zero-padding
  */
 static size_t bzimage_load_initrd ( struct image *image,
 				    struct image *initrd,
 	}
 	offset += initrd->len;
 
-	/* Round up to multiple of INITRD_ALIGN and zero-pad */
+	/* Zero-pad to next INITRD_ALIGN boundary */
 	pad_len = ( ( -offset ) & ( INITRD_ALIGN - 1 ) );
 	if ( address )
 		memset_user ( address, offset, 0, pad_len );
-	offset += pad_len;
 
 	return offset;
 }
 
 		/* Calculate length */
 		len += bzimage_load_initrd ( image, initrd, UNULL );
+		len = bzimage_align ( len );
 
 		DBGC ( image, "bzImage %p initrd %p from [%#08lx,%#08lx)%s%s\n",
 		       image, initrd, user_to_phys ( initrd->data, 0 ),
 	struct image *other;
 	userptr_t top;
 	userptr_t dest;
+	size_t offset;
 	size_t len;
 
 	/* Reshuffle initrds into desired order */
 		return;
 
 	/* Find highest usable address */
-	top = userptr_add ( highest->data,
-			    ( ( highest->len + INITRD_ALIGN - 1 ) &
-			      ~( INITRD_ALIGN - 1 ) ) );
+	top = userptr_add ( highest->data, bzimage_align ( highest->len ) );
 	if ( user_to_phys ( top, 0 ) > bzimg->mem_limit )
 		top = phys_to_user ( bzimg->mem_limit );
 	DBGC ( image, "bzImage %p loading initrds from %#08lx downwards\n",
 		/* Calculate cumulative length of following
 		 * initrds (including padding).
 		 */
-		len = 0;
+		offset = 0;
 		for_each_image ( other ) {
 			if ( other == initrd )
-				len = 0;
-			len += bzimage_load_initrd ( image, other, UNULL );
+				offset = 0;
+			offset += bzimage_load_initrd ( image, other, UNULL );
+			offset = bzimage_align ( offset );
 		}
 
 		/* Load initrd at this address */
-		dest = userptr_add ( top, -len );
-		bzimage_load_initrd ( image, initrd, dest );
+		dest = userptr_add ( top, -offset );
+		len = bzimage_load_initrd ( image, initrd, dest );
 
 		/* Record initrd location */
-		if ( ! bzimg->ramdisk_image ) {
+		if ( ! bzimg->ramdisk_image )
 			bzimg->ramdisk_image = user_to_phys ( dest, 0 );
-			bzimg->ramdisk_size = len;
-		}
+		bzimg->ramdisk_size = ( user_to_phys ( dest, len ) -
+					bzimg->ramdisk_image );
 	}
+	DBGC ( image, "bzImage %p initrds at [%#08lx,%#08lx)\n",
+	       image, bzimg->ramdisk_image,
+	       ( bzimg->ramdisk_image + bzimg->ramdisk_size ) );
 }
 
 /**