Btrfs-progs: add a free space cache checker to fsck V2

In trying to track down a weird tree log problem I wanted to make sure that the
free space cache was actually valid, which we currently have no way of doing.
So this patch adds a bunch of support for the free space cache code and then a
checker to fsck.  Basically we go through and if we can actually load the free
space cache then we will walk the extent tree and verify that the free space
cache exactly matches what is in the extent tree.  Hopefully this will always be
correct, the only time it wouldn't is if the extent tree is corrupt or we have
some sort of awful bug in the free space cache.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/extent_io.c b/extent_io.c
index 78deb502..5093aeb2 100644
--- a/extent_io.c
+++ b/extent_io.c
@@ -27,6 +27,8 @@
 #include "kerncompat.h"
 #include "extent_io.h"
 #include "list.h"
+#include "ctree.h"
+#include "volumes.h"
 
 u64 cache_soft_max = 1024 * 1024 * 256;
 u64 cache_hard_max = 1 * 1024 * 1024 * 1024;
@@ -696,6 +698,55 @@ out:
 	return ret;
 }
 
+int read_data_from_disk(struct btrfs_fs_info *info, void *buf, u64 offset,
+			u64 bytes, int mirror)
+{
+	struct btrfs_multi_bio *multi = NULL;
+	struct btrfs_device *device;
+	u64 bytes_left = bytes;
+	u64 read_len;
+	u64 total_read = 0;
+	int ret;
+
+	while (bytes_left) {
+		read_len = bytes_left;
+		ret = btrfs_map_block(&info->mapping_tree, READ, offset,
+				      &read_len, &multi, mirror, NULL);
+		if (ret) {
+			fprintf(stderr, "Couldn't map the block %Lu\n",
+				offset);
+			return -EIO;
+		}
+		device = multi->stripes[0].dev;
+
+		read_len = min(bytes_left, read_len);
+		if (device->fd == 0) {
+			kfree(multi);
+			return -EIO;
+		}
+
+		ret = pread(device->fd, buf + total_read, read_len,
+			    multi->stripes[0].physical);
+		kfree(multi);
+		if (ret < 0) {
+			fprintf(stderr, "Error reading %Lu, %d\n", offset,
+				ret);
+			return ret;
+		}
+		if (ret != read_len) {
+			fprintf(stderr, "Short read for %Lu, read %d, "
+				"read_len %Lu\n", offset, ret, read_len);
+			return -EIO;
+		}
+
+		bytes_left -= read_len;
+		offset += read_len;
+		total_read += read_len;
+	}
+
+	return 0;
+}
+
 int set_extent_buffer_uptodate(struct extent_buffer *eb)
 {
 	eb->flags |= EXTENT_UPTODATE;