master

MMasahiro Yamadakbuild: trace functions in subdirectories of lib/

b16838c6创建于 2020年8月10日历史提交

文件	最后提交记录	最后更新时间
Makefile	rslib: Add tests for the encoder and decoder A Reed-Solomon code with minimum distance d can correct any error and erasure pattern that satisfies 2 * #error + #erasures < d. If the error correction capacity is exceeded, then correct decoding cannot be guaranteed. The decoder must, however, return a valid codeword or report failure. There are two main tests: - Check for correct behaviour up to the error correction capacity - Check for correct behaviour beyond error corrupted capacity Both tests are simple: 1. Generate random data 2. Encode data with the chosen code 3. Add errors and erasures to data 4. Decode the corrupted word 5. Check for correct behaviour When testing up to capacity we test for: - Correct decoding - Correct return value (i.e. the number of corrected symbols) - That the returned error positions are correct There are two kinds of erasures; the erased symbol can be corrupted or not. When counting the number of corrected symbols, erasures without symbol corruption should not be counted. Similarly, the returned error positions should only include positions where a correction is necessary. We run the up to capacity tests for three different interfaces of decode_rs: - Use the correction buffers - Use the correction buffers with syndromes provided by the caller - Error correction in place (does not check the error positions) When testing beyond capacity test for silent failures. A silent failure is when the decoder returns success but the returned word is not a valid codeword. There are a couple of options for the tests: - Verbosity. - Whether to test for correct behaviour beyond capacity. Default is to test beyond capacity. - Whether to allow erasures without symbol corruption. Defaults to yes. Note that the tests take a couple of minutes to complete. Signed-off-by: Ferdinand Blomqvist <ferdinand.blomqvist@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20190620141039.9874-2-ferdinand.blomqvist@gmail.com	6 年前
decode_rs.c	rslib: Fix remaining decoder flaws The decoder is flawed in the following ways: - The decoder sometimes fails silently, i.e. it announces success but returns a word that is not a codeword. - The return value of the decoder is incoherent with respect to how fixed erasures are counted. If the word to be decoded is a codeword, then the decoder always returns zero even if some erasures are given. On the other hand, if the word to be decoded contains errors, then the number of erasures is always included in the count of corrected symbols. So the decoder handles erasures without symbol corruption inconsistently. This inconsistency probably doesn't affect anyone using the decoder, but it is inconsistent with the documentation. - The error positions returned in eras_pos include all erasures, but the corrections are only set in the correction buffer if there actually is a symbol error. So if there are erasures without symbol corruption, then the correction buffer will contain errors (unless initialized to zero before calling the decoder) or some values will be unset (if the correction buffer is uninitialized). - When correcting data in-place the decoder does not correct errors in the parity. On the other hand, when returning the errors in correction buffers, errors in the parity are included. The respective fixed are: - The syndrome of a codeword is always zero, and the syndrome is linear, .i.e, S(x+e) = S(x) + S(e). So compute the syndrome for the error and check whether it equals the syndrome of the received word. If it does, then we have decoded to a valid codeword, otherwise we know that we have an uncorrectable error. Fortunately, some unrecoverable error conditions can be detected earlier in the decoding, which saves some processing power. - Simply count and return the number of symbols actually corrected. - Make sure to only return positions where symbols were corrected. - Also fix errors in parity when correcting in-place. Another option would be to completely disregard errors in the parity, but then the interface makes it impossible to write tests that test for silent failures. Other changes: - Only fill the correction buffer and error position buffer if both of them are provided. Otherwise correct in place. Previously the error position buffer was always populated with the positions of the corrected errors, irrespective of whether a correction buffer was supplied or not. The rationale for this change is that there seems to be two use cases for the decoder; correct in-place or use the correction buffers. The caller does not need the positions of the corrected errors when in-place correction is used. If in-place correction is not used, then both the correction buffer and error position buffer need to be populated. Signed-off-by: Ferdinand Blomqvist <ferdinand.blomqvist@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20190620141039.9874-8-ferdinand.blomqvist@gmail.com	6 年前
encode_rs.c	rslib: Split rs control struct The decoder library uses variable length arrays on stack. To get rid of them it would be simple to allocate fixed length arrays on stack, but those might become rather large. The other solution is to allocate the buffers in the rs control structure, but this cannot be done as long as the structure can be shared by several users. Sharing is desired because the RS polynom tables are large and initialization is time consuming. To solve this split the codec information out of the control structure and have a pointer to a shared codec in it. Instantiate the control structure for each user, create a new codec if no shareable is avaiable yet. Adjust all affected usage sites to the new scheme. This allows to add per instance decoder buffers to the control structure later on. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Boris Brezillon <boris.brezillon@bootlin.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Kees Cook <keescook@chromium.org> Cc: Segher Boessenkool <segher@kernel.crashing.org> Cc: Kernel Hardening <kernel-hardening@lists.openwall.com> Cc: Richard Weinberger <richard@nod.at> Cc: Mike Snitzer <snitzer@redhat.com> Cc: Anton Vorontsov <anton@enomsg.org> Cc: Colin Cross <ccross@android.com> Cc: Andrew Morton <akpm@linuxfoundation.org> Cc: David Woodhouse <dwmw2@infradead.org> Cc: Alasdair Kergon <agk@redhat.com> Signed-off-by: Kees Cook <keescook@chromium.org>	8 年前
reed_solomon.c	rslib: Update documentation The decoder returns the number of corrected symbols, not bits. The caller provided syndrome must be in index form. Signed-off-by: Ferdinand Blomqvist <ferdinand.blomqvist@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20190620141039.9874-7-ferdinand.blomqvist@gmail.com	6 年前
test_rslib.c	rslib: Make some functions static Fix sparse warnings: lib/reed_solomon/test_rslib.c:313:5: warning: symbol 'ex_rs_helper' was not declared. Should it be static? lib/reed_solomon/test_rslib.c:349:5: warning: symbol 'exercise_rs' was not declared. Should it be static? lib/reed_solomon/test_rslib.c:407:5: warning: symbol 'exercise_rs_bc' was not declared. Should it be static? Reported-by: Hulk Robot <hulkci@huawei.com> Signed-off-by: YueHaibing <yuehaibing@huawei.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: <ferdinand.blomqvist@gmail.com> Link: https://lkml.kernel.org/r/20190702061847.26060-1-yuehaibing@huawei.com	6 年前