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+btrfs-zero-log - clear out log tree
+*btrfs-zero-log* <dev>
+*btrfs-zero-log* will remove the log tree if log tree is corrupt, which will
+allow you to mount the filesystem again.
+The common case where this happens has been fixed a long time ago,
+so it is unlikely that you will see this particular problem.
+One can determine whether *btrfs-zero-log* is needed according to the kernel
+? replay_one_dir_item+0xb5/0xb5 [btrfs]
+? walk_log_tree+0x9c/0x19d [btrfs]
+? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
+? btrfs_recover_log_trees+0x195/0x29c [btrfs]
+? replay_one_dir_item+0xb5/0xb5 [btrfs]
+? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
+? open_ctree+0xff6/0x132c [btrfs]
+If the errors are like above, then *btrfs-zero-log* should be used to clear
+the log and the filesystem may be mounted normally again.
+NOTE: If you use btrfs as the root filesystem, you may want to include
+*btrfs-zero-log* into initramdisk if the log problems hits you often.
+*btrfs-zero-log* will return 0 if no error happened.
+Other exit code means some problems happened.