2018年11月22日(木) 16:06 Al Viro <viro@xxxxxxxxxxxxxxxxxx>: > > Can you show me where does POSIX/SuS/whatever it's called these days promise > that kind of atomicity? No. I couldn't found it. That's why I previously posted RFC Patch: https://marc.info/?t=154237277900001&r=1&w=2 I wasn't sure this is a bug in the kernel or not. > that kind of atomicity? TBH, I would be very surprised if any Unix promised > to have file size updated no more than once per write(2). Any userland code > that relies on such property is, as minimum, non-portable and I would argue > that it is outright broken. Thanks. Now It's clear. It is not a bug in the kernel, but in userspace if `tail` assumes such atomicity. > Note, BTW, that your example depends upon rather non-obvious details of echo > implementation, starting with the bufferization logics used by particular > shell. And AFAICS ash(1) ends up with possibility of more than one write(2) I've never imagined such a difference in echo implementation, thanks.
