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eb386617be
Add a tracepoint for downcasting private errors to standard errors, so they can be recovered even when not logged; also, add some documentation. Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
31 lines
1.4 KiB
ReStructuredText
31 lines
1.4 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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bcachefs private error codes
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----------------------------
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In bcachefs, as a hard rule we do not throw or directly use standard error
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codes (-EINVAL, -EBUSY, etc.). Instead, we define private error codes as needed
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in fs/bcachefs/errcode.h.
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This gives us much better error messages and makes debugging much easier. Any
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direct uses of standard error codes you see in the source code are simply old
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code that has yet to be converted - feel free to clean it up!
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Private error codes may subtype another error code, this allows for grouping of
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related errors that should be handled similarly (e.g. transaction restart
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errors), as well as specifying which standard error code should be returned at
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the bcachefs module boundary.
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At the module boundary, we use bch2_err_class() to convert to a standard error
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code; this also emits a trace event so that the original error code be
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recovered even if it wasn't logged.
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Do not reuse error codes! Generally speaking, a private error code should only
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be thrown in one place. That means that when we see it in a log message we can
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see, unambiguously, exactly which file and line number it was returned from.
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Try to give error codes names that are as reasonably descriptive of the error
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as possible. Frequently, the error will be logged at a place far removed from
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where the error was generated; good names for error codes mean much more
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descriptive and useful error messages.
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