Commit d32f31f411 ("btrfs-tree: harden
`rlower_bound` against exceptional objects") passes the first btrfs item
in the result set that is above upper_bound up to `seek_backward`.
This is somewhat wasteful as `seek_backward` cannot use such a result.
Reverse that change in behavior, while keeping the rest of the other
commit.
This introduces a new case, where the search ioctl is producing items
that are above upper bound, but there are no items in the result set,
which continues looping until the end of the filesystem is reached.
Handle that by setting an explicit exit variable.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Rearrange the logic in `rlower_bound` so it can cope with a tree
that contains mostly block-aligned objects, with a few exceptions
filtered out by `hdr_stop`.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
In some cases functions already had existing debug stream support
which can be redirected to the new interface. In other cases, new
debug messages are added.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
BtrfsFsTreeFetcher was used for early versions of the extent scanner, but
neither subvol nor extent scan now needs an object that is both persistent
and configured to access only one subvol. BtrfsExtentDataFetcher does
the same thing in that case.
Clarify the comments on what the remaining classes do, so that
BtrfsFsTreeFetcher doesn't get inadvertently reinvented in the future.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Binary searches can be extremely slow if the target bytenr is near a
metadata block group, because metadata items are not visible to the
binary search algorithm. In a non-mixed-bg filesystem, there can be
hundreds of thousands of metadata items between data extent items, and
since the binary search algorithm can't see them, it will run searches
that iterate over hundreds of thousands of objects about a dozen times.
This is less of a problem for mixed-bg filesystems because the data and
metadata blocks are not isolated from each other. The binary search
algorithm still can't see the metadata items, but there are usually
some data items close by to prevent the linear item filter from running
too long.
Introduce a new fetcher class (all the good names were taken) that tracks
where the end of the current block group is. When the end of the current
block group is reached in the linear search, skip ahead to a block group
that can contain data items.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
btrfs-tree provides classes for low-level access to btrfs tree objects.
An item class is provided to decode polymorphic btrfs item fields.
Several tree classes provide forward and backward iteration over raw
object items at different tree levels.
A csum tree class provides convenient access to csums by bytenr,
supporting all current btrfs csum types.
Wrapper classes for inode and subvol items provide direct access to
btrfs metadata fields without clumsy stat() wrappers or ioctls.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
