BtrFS support. Written by me (Vladimir) with important bugfixes and

even more important testing by Colin.

	* Makefile.util.def (libgrubmods.a): Add crc.c and gzio.c
	* grub-core/Makefile.core.def (btrfs): Add crc.c.
	* grub-core/fs/btrfs.c: Stub replaced with real implementation.
	* grub-core/io/gzio.c (grub_gzio): New fields mem_input_size,
	mem_input_off and mem_input. All users updated to accept in-RAM input.
	(gzio_seek): New function.
	(test_zlib_header): Likewise.
	(grub_gzio_read): Likewise.
	(grub_zlib_decompress): Likewise.
	* grub-core/kern/emu/getroot.c (grub_find_root_device_from_mountinfo):
	Accept partial and non-virtual mounts.
	(grub_guess_root_device): Do rescanning after device_from_mountinfo to
	avoid receiving /dev/dm-X as device.
	* grub-core/kern/emu/misc.c (grub_make_system_path_relative_to_its_root):
	Handle bind and partial mounts.
	* grub-core/lib/crc.c: New file.
	* include/grub/deflate.h: Likewise.
	* include/grub/emu/misc.h (grub_find_root_device_from_mountinfo): New
	proto.
	* include/grub/lib/crc.h: New file.

grub-core/lib/crc.c

@@ -0,0 +1,75 @@
+/* crc.c - crc function  */
+/*
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2008  Free Software Foundation, Inc.
+ *
+ *  GRUB is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  GRUB is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/types.h>
+#include <grub/lib/crc.h>
+
+static grub_uint32_t crc32c_table [256];
+
+static void
+init_crc32c_table (void)
+{
+  auto grub_uint32_t reflect (grub_uint32_t ref, int len);
+  grub_uint32_t reflect (grub_uint32_t ref, int len)
+    {
+      grub_uint32_t result = 0;
+      int i;
+
+      for (i = 1; i <= len; i++)
+        {
+          if (ref & 1)
+            result |= 1 << (len - i);
+          ref >>= 1;
+        }
+
+      return result;
+    }
+
+  grub_uint32_t polynomial = 0x1edc6f41;
+  int i, j;
+
+  for(i = 0; i < 256; i++)
+    {
+      crc32c_table[i] = reflect(i, 8) << 24;
+      for (j = 0; j < 8; j++)
+        crc32c_table[i] = (crc32c_table[i] << 1) ^
+            (crc32c_table[i] & (1 << 31) ? polynomial : 0);
+      crc32c_table[i] = reflect(crc32c_table[i], 32);
+    }
+}
+
+grub_uint32_t
+grub_getcrc32c (grub_uint32_t crc, const void *buf, int size)
+{
+  int i;
+  const grub_uint8_t *data = buf;
+
+  if (! crc32c_table[1])
+    init_crc32c_table ();
+
+  crc^= 0xffffffff;
+
+  for (i = 0; i < size; i++)
+    {
+      crc = (crc >> 8) ^ crc32c_table[(crc & 0xFF) ^ *data];
+      data++;
+    }
+
+  return crc ^ 0xffffffff;
+}