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bcachefs format on a big-endian (s390x) machine crashes down in the rhashtable code imported from the kernel. The reason this occurs lies within the rht_lock() -> bit_spin_lock() code, the latter of which casts bitmaps down to 32-bits to satisfy the requirements of the futex interface. The specific problem here is that a 64 -> 32 bit cast doesn't refer to the lower 8 bytes on a big endian machine, which means setting bit number 0 in the 32-bit map actually corresponds to bit 32 in the 64-bit map. The rhashtable code specifically uses bit zero of the bucket pointer for exclusion and uses native bitops elsewhere (i.e. __rht_ptr()) to identify NULL pointers. If bit 32 of the pointer is set by the locking code instead of bit 0, an otherwise NULL pointer looks like a non-NULL value and results in a segfault. The bit spinlock code imported by the kernel is originally intended to work with unsigned long. The kernel code is able to throttle the cpu directly when under lock contention, while the userspace implementation relies on the futex primitives to emulate reliable blocking. Since the futex interface introduces the 32-bit requirement, isolate the associated userspace hack to that particular code. Restore the native bitmap behavior of the bit spinlock code to address the rhashtable problem described above. Since this is not compatible with the futex interface, create a futex wrapper specifically to convert the native bitmap type to a 32-bit virtual address and mask value for the purposes of waiting/waking when under lock contention. Signed-off-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
bcachefs-tools
Userspace tools and docs for bcachefs
Bcachefs is an advanced new filesystem for Linux, with an emphasis on reliability and robustness and the complete set of features one would expect from a modern filesystem.
This repo primarily consists of the following:
- bcachefs tool, the reason this repo exists.
- {mkfs,mount,fsck}.bcachefs utils, which is just wrappers calling the corresponding subcommands in the main tool
- docs in the form of man-pages and a user manual
Please refer to the main site for getting started An in-depth user manual is (also) found on the official website
Build and install
Refer to INSTALL.md
Bug reports and contributions
- The official mailing list, linux-bcachefs@vger.kernel.org
- IRC: #bcache on OFTC (irc.oftc.net). Although, note that it can be easily missed.