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os: clarify documentation for O_TRUNC #28699

bcmills opened this Issue Nov 9, 2018 · 2 comments


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bcmills commented Nov 9, 2018

The comment for os.O_TRUNC currently says:

O_TRUNC int = syscall.O_TRUNC // if possible, truncate file when opened.

The “if possible” part of that comment is ambiguous: on Linux it seems to mean “if the file is a regular file or symlink to a regular file” (i.e., not a stream like /dev/stdout), but it could be “impossible” to truncate the file for other reasons (such as a permission error), and os.OpenFile with os.O_TRUNC seems to report an error in those cases.

We should drop the “if possible” phrase and instead explicitly document the conditions under which O_TRUNC is ignored.

@bcmills bcmills added this to the Go1.12 milestone Nov 9, 2018


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bcmills commented Nov 9, 2018


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robpike commented Nov 10, 2018

I fear that making the os package document every aspect, for every OS, of the calls it wraps is a Sisyphean endeavor and not worth pursuing.

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