[PATCH 02/10] btrfs-progs: Add extent buffer bitmap manipulation infrastructure

[Nikolay Borisov <nborisov@suse.com>]

Those functions are in preparation for adding the freespace tree
repair code since it needs to be able to deal with bitmap based fsts.
This patch adds extent_buffer_bitmap_set and extent_buffer_bitmap_clear
functions. Since in userspace we don't have to deal with page mappings
their implementation is vastly simplified by simply setting each bit in
the passed range.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 extent_io.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 extent_io.h |  4 ++++
 2 files changed, 60 insertions(+)

diff --git a/extent_io.c b/extent_io.c
index 198492699438..de47c2c59ae9 100644
--- a/extent_io.c
+++ b/extent_io.c
@@ -204,6 +204,62 @@ static int clear_state_bit(struct extent_io_tree *tree,
 	return ret;
 }
 
+/**
+ * extent_buffer_bitmap_set - set an area of a bitmap
+ * @eb: the extent buffer
+ * @start: offset of the bitmap item in the extent buffer
+ * @pos: bit number of the first bit
+ * @len: number of bits to set
+ */
+void extent_buffer_bitmap_set(struct extent_buffer *eb, unsigned long start,
+                              unsigned long pos, unsigned long len)
+{
+	u8 *p = (u8 *)eb->data + start + BIT_BYTE(pos);
+	const unsigned int size = pos + len;
+	int bits_to_set = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
+	u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(pos);
+
+	while (len >= bits_to_set) {
+		*p |= mask_to_set;
+		len -= bits_to_set;
+		bits_to_set = BITS_PER_BYTE;
+		mask_to_set = ~0;
+		p++;
+	}
+	if (len) {
+		mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
+		*p |= mask_to_set;
+	}
+}
+
+
+/**
+ * extent_buffer_bitmap_clear - clear an area of a bitmap
+ * @eb: the extent buffer
+ * @start: offset of the bitmap item in the extent buffer
+ * @pos: bit number of the first bit
+ * @len: number of bits to clear
+ */
+void extent_buffer_bitmap_clear(struct extent_buffer *eb, unsigned long start,
+                                unsigned long pos, unsigned long len)
+{
+	u8 *p = (u8 *)eb->data + start + BIT_BYTE(pos);
+	const unsigned int size = pos + len;
+	int bits_to_clear = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
+	u8 mask_to_clear = BITMAP_FIRST_BYTE_MASK(pos);
+
+	while (len >= bits_to_clear) {
+		*p &= ~mask_to_clear;
+		len -= bits_to_clear;
+		bits_to_clear = BITS_PER_BYTE;
+		mask_to_clear = ~0;
+		p++;
+	}
+	if (len) {
+		mask_to_clear &= BITMAP_LAST_BYTE_MASK(size);
+		*p &= ~mask_to_clear;
+	}
+}
 /*
  * clear some bits on a range in the tree.
  */
diff --git a/extent_io.h b/extent_io.h
index d407d93d617e..b67c6fc40e89 100644
--- a/extent_io.h
+++ b/extent_io.h
@@ -175,4 +175,8 @@ int read_data_from_disk(struct btrfs_fs_info *info, void *buf, u64 offset,
 			u64 bytes, int mirror);
 int write_data_to_disk(struct btrfs_fs_info *info, void *buf, u64 offset,
 		       u64 bytes, int mirror);
+void extent_buffer_bitmap_clear(struct extent_buffer *eb, unsigned long start,
+                                unsigned long pos, unsigned long len);
+void extent_buffer_bitmap_set(struct extent_buffer *eb, unsigned long start,
+                              unsigned long pos, unsigned long len);
 #endif
-- 
2.7.4