This is some cpp abuse that is used to generate functions.
to read and modify the extent buffers. Look for 'deeply nasty code' below
for a longer description of how it all works.
Signed-off-by: Chris Mason <chris.mason@xxxxxxxxxx>
diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c
new file mode 100644
index 0000000..c0f7eca
--- /dev/null
+++ b/fs/btrfs/struct-funcs.c
@@ -0,0 +1,139 @@
+/*
+ * Copyright (C) 2007 Oracle. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program 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 this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <linux/highmem.h>
+
+/* this is some deeply nasty code. ctree.h has a different
+ * definition for this BTRFS_SETGET_FUNCS macro, behind a #ifndef
+ *
+ * The end result is that anyone who #includes ctree.h gets a
+ * declaration for the btrfs_set_foo functions and btrfs_foo functions
+ *
+ * This file declares the macros and then #includes ctree.h, which results
+ * in cpp creating the function here based on the template below.
+ *
+ * These setget functions do all the extent_buffer related mapping
+ * required to efficiently read and write specific fields in the extent
+ * buffers. Every pointer to metadata items in btrfs is really just
+ * an unsigned long offset into the extent buffer which has been
+ * cast to a specific type. This gives us all the gcc type checking.
+ *
+ * The extent buffer api is used to do all the kmapping and page
+ * spanning work required to get extent buffers in highmem and have
+ * a metadata blocksize different from the page size.
+ *
+ * The macro starts with a simple function prototype declaration so that
+ * sparse won't complain about it being static.
+ */
+
+#define BTRFS_SETGET_FUNCS(name, type, member, bits) \
+u##bits btrfs_##name(struct extent_buffer *eb, type *s); \
+void btrfs_set_##name(struct extent_buffer *eb, type *s, u##bits val); \
+u##bits btrfs_##name(struct extent_buffer *eb, \
+ type *s) \
+{ \
+ unsigned long part_offset = (unsigned long)s; \
+ unsigned long offset = part_offset + offsetof(type, member); \
+ type *p; \
+ /* ugly, but we want the fast path here */ \
+ if (eb->map_token && offset >= eb->map_start && \
+ offset + sizeof(((type *)0)->member) <= eb->map_start + \
+ eb->map_len) { \
+ p = (type *)(eb->kaddr + part_offset - eb->map_start); \
+ return le##bits##_to_cpu(p->member); \
+ } \
+ { \
+ int err; \
+ char *map_token; \
+ char *kaddr; \
+ int unmap_on_exit = (eb->map_token == NULL); \
+ unsigned long map_start; \
+ unsigned long map_len; \
+ u##bits res; \
+ err = map_extent_buffer(eb, offset, \
+ sizeof(((type *)0)->member), \
+ &map_token, &kaddr, \
+ &map_start, &map_len, KM_USER1); \
+ if (err) { \
+ __le##bits leres; \
+ read_eb_member(eb, s, type, member, &leres); \
+ return le##bits##_to_cpu(leres); \
+ } \
+ p = (type *)(kaddr + part_offset - map_start); \
+ res = le##bits##_to_cpu(p->member); \
+ if (unmap_on_exit) \
+ unmap_extent_buffer(eb, map_token, KM_USER1); \
+ return res; \
+ } \
+} \
+void btrfs_set_##name(struct extent_buffer *eb, \
+ type *s, u##bits val) \
+{ \
+ unsigned long part_offset = (unsigned long)s; \
+ unsigned long offset = part_offset + offsetof(type, member); \
+ type *p; \
+ /* ugly, but we want the fast path here */ \
+ if (eb->map_token && offset >= eb->map_start && \
+ offset + sizeof(((type *)0)->member) <= eb->map_start + \
+ eb->map_len) { \
+ p = (type *)(eb->kaddr + part_offset - eb->map_start); \
+ p->member = cpu_to_le##bits(val); \
+ return; \
+ } \
+ { \
+ int err; \
+ char *map_token; \
+ char *kaddr; \
+ int unmap_on_exit = (eb->map_token == NULL); \
+ unsigned long map_start; \
+ unsigned long map_len; \
+ err = map_extent_buffer(eb, offset, \
+ sizeof(((type *)0)->member), \
+ &map_token, &kaddr, \
+ &map_start, &map_len, KM_USER1); \
+ if (err) { \
+ __le##bits val2; \
+ val2 = cpu_to_le##bits(val); \
+ write_eb_member(eb, s, type, member, &val2); \
+ return; \
+ } \
+ p = (type *)(kaddr + part_offset - map_start); \
+ p->member = cpu_to_le##bits(val); \
+ if (unmap_on_exit) \
+ unmap_extent_buffer(eb, map_token, KM_USER1); \
+ } \
+}
+
+#include "ctree.h"
+
+void btrfs_node_key(struct extent_buffer *eb,
+ struct btrfs_disk_key *disk_key, int nr)
+{
+ unsigned long ptr = btrfs_node_key_ptr_offset(nr);
+ if (eb->map_token && ptr >= eb->map_start &&
+ ptr + sizeof(*disk_key) <= eb->map_start + eb->map_len) {
+ memcpy(disk_key, eb->kaddr + ptr - eb->map_start,
+ sizeof(*disk_key));
+ return;
+ } else if (eb->map_token) {
+ unmap_extent_buffer(eb, eb->map_token, KM_USER1);
+ eb->map_token = NULL;
+ }
+ read_eb_member(eb, (struct btrfs_key_ptr *)ptr,
+ struct btrfs_key_ptr, key, disk_key);
+}
--
1.6.0.2
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