readv and writev are in the single unix spec...and yes ...
On some systems they might just be implemented as a loop inside the library, or even as a macro.
You sure?
Requirements like this: http://www.opengroup.org/onlinepubs/007908799/xsh/write.html "Write requests of {PIPE_BUF} bytes or less will not be interleaved with data from other processes doing writes on the same pipe." make me think that it couldn't be just a macro; and if it were a loop in the library it seems it'd still have to make sure it's done with a single write system call.
(yeah, I know that requirement is just for pipes; and I suppose they could write a loop for normal files and a different special case for pipes; but I'd be surprised).
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