The Linux kernel's btrfs headers are better than the libbtrfs-dev headers:
- the libbtrfs-dev headers have C++ language compatibility issues
- upstream version in Linux kernel is more accurate and up to date
- macros in libbtrfs-dev's ctree.h hide information that would
enable bees to perform runtime buffer length checking
- enum types whose presence cannot be detected with #ifdef
When accessing members of metadata items from the filesystem, we want
to verify that the member we are accessing is within the boundaries of
the item that was retrieved; otherwise, a memory access violation may
occur or garbage may be returned to the caller. A simple C++ template,
given a pointer to a structure member and a buffer, can determine that
the buffer contains enough bytes to safely access a struct member.
This was implemented back in 2016, but left unused due to ctree.h issues.
Some btrfs metadata structures have variable length despite using a
fixed-size in-memory structure. The members that appear earliest in
the structure contain information about which following members of the
structure are used. The item stored in the filesystem is truncated after
the last used member, and all following members must not be accessed.
'btrfs_stack_*' accessor macros obscure the memory boundaries of the
members they access, which makes it impossible for a C++ template to
verify the memory access. If the template checks the length of the
entire structure, it will find an access violation for variable-length
metadata items because the item is rarely large enough for the entire
structure.
Get rid of all the libbtrfs-dev accessor macros and reimplement them
with the necessary buffer length checks.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Use uint8_t when we mean uint8_t, i.e. vector<uint8_t> instead of
vector<char>.
Add a template parameter instead of vector so we can swap in a
non-copying data type.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Define a local copy of the header that has fields for the csum type
and length, so we can build in places that haven't caught up to kernel
5.5 headers yet.
The reason why the csum type and length are not unconditionally filled
in eludes me. csum_length is necessarily non-zero, and the cost of
the conditional is worse than the cost of the copy, so the whole flags
dance is a WTF...but it's part of the kernel API now, so it's too late
to NAK it.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Perf blames this operator for >1% of instructions with -O2, and
70% of instructions without -O2.
Let the compiler inline the function.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
The requested size may not match the final size of the container,
so consistently use the container's size after prepare(), not the
requested size.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
It is not possible to emulate extent-same by clone in a safe way.
EXTENT_SAME has been supported in btrfs since kernel 3.13, which
is much too old to contemplate running bees on.
Remove this dangerous and unused function.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Make sure the result set is empty before running the ioctl in case
something tries to consume the result without checking the error status.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
If we are not zero-filling containers then the overhead of allocating them
on each use is negligible. The effect that the thread_local containers
were having on RAM usage was very non-negligible.
Use dynamic containers (members or stack objects) for better control
of object lifetimes and much lower peak RAM usage. They're a tiny bit
faster, too.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
Automatically fall back to LOGICAL_INO if LOGICAL_INO_V2 fails and no
_V2 flags are used.
Add methods to set the flags argument with build portability to older
headers.
Use thread_local storage for the somewhat large buffers used by
LOGICAL_INO_V2 (and other users of BtrfsDataContainer like INO_PATHS).
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
The memset is just doing an assignment from one dereferenced pointer to
another, so do an assignment to keep GCC 8 happy.
Fixes: https://github.com/Zygo/bees/issues/64
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
perf blames the SEARCH_V2 ioctl wrapper for a lot of time spent in malloc.
Use a thread_local buffer for ioctl results, and reuse it between runs.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
(cherry picked from commit e509210428951e645d33916694a17aed1950991d)
This gets rid of some more big memsets. It may replace them
with a lot of tiny mallocs, though. If this turns out to be
a bad idea then at least we can easily revert the change.
We really do need some large buffers for BtrfsIoctlSearchKey in some
cases, but we don't need to zero them out first. Don't do that so we
save some CPU.
Reduce the default buffer size to 4K because most BISK users don't get
need much more than 1K. Set the buffer size explicitly to the product of
the number of items and the desired item size in the places that really
need a lot of items.
I accidentally did a pre-push verification on a 32-bit build host.
There were a surprisingly small number of problems, so fix them.
Bees now builds on a 32-bit host. Let's not update README just yet,
though: the 32-bit ioctl support fails immediately after startup on a
64-bit kernel.
