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[ Upstream commit 9dedc73a4658ebcc0c9b58c3cb84e9ac80122213 ] The Linux BTT implementation assumes that log entries will never have the 'zero' flag set, and indeed it never sets that flag for log entries itself. However, the UEFI spec is ambiguous on the exact format of the LBA field of a log entry, specifically as to whether it should include the additional flag bits or not. While a zero bit doesn't make sense in the context of a log entry, other BTT implementations might still have it set. If an implementation does happen to have it set, we would happily read it in as the next block to write to for writes. Since a high bit is set, it pushes the block number out of the range of an 'arena', and we fail such a write with an EIO. Follow the robustness principle, and tolerate such implementations by stripping out the zero flag when populating the free list during initialization. Additionally, use the same stripped out entries for detection of incomplete writes and map restoration that happens at this stage. Add a sysfs file 'log_zero_flags' that indicates the ability to accept such a layout to userspace applications. This enables 'ndctl check-namespace' to recognize whether the kernel is able to handle zero flags, or whether it should attempt a fix-up under the --repair option. Cc: Dan Williams <dan.j.williams@intel.com> Reported-by: Dexuan Cui <decui@microsoft.com> Reported-by: Pedro d'Aquino Filocre F S Barbuda <pbarbuda@microsoft.com> Tested-by: Dexuan Cui <decui@microsoft.com> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.