Mixed back reference (FORWARD ROLLING FORMAT CHANGE)

This commit introduces a new kind of back reference for btrfs metadata.
Once a filesystem has been mounted with this commit, IT WILL NO LONGER
BE MOUNTABLE BY OLDER KERNELS.

The new back ref provides information about pointer's key, level and in which
tree the pointer lives. This information allow us to find the pointer by
searching the tree. The shortcoming of the new back ref is that it only works
for pointers in tree blocks referenced by their owner trees.

This is mostly a problem for snapshots, where resolving one of these fuzzy back
references would be O(number_of_snapshots) and quite slow.  The solution used
here is to use the fuzzy back references in the common case where a given tree
block is only referenced by one root, and use the full back references when
multiple roots have a reference

1 files changed, 1 insertions, 0 deletions

diff --git a/crc32c.h b/crc32c.h
index 6d20a953..72f15120 100644
--- a/crc32c.h
+++ b/crc32c.h
@@ -24,4 +24,5 @@
 u32 crc32c_le(u32 seed, unsigned char const *data, size_t length);
 
 #define crc32c(seed, data, length) crc32c_le(seed, (unsigned char const *)data, length)
+#define btrfs_crc32c crc32c
 #endif