Date: Fri, 14 Aug 2015 22:07:09 +0200 From: Jilles Tjoelker <jilles@stack.nl> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-current@freebsd.org, Julian Elischer <julian@freebsd.org>, "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org> Subject: Re: futimens and utimensat vs birthtime Message-ID: <20150814200709.GB88901@stack.nl> In-Reply-To: <2405496.WdPSxGzEuT@ralph.baldwin.cx> References: <55CDFF32.7050601@freebsd.org> <2405496.WdPSxGzEuT@ralph.baldwin.cx>
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On Fri, Aug 14, 2015 at 10:39:41AM -0700, John Baldwin wrote: > On Friday, August 14, 2015 10:46:10 PM Julian Elischer wrote: > > I would like to implement this call. but would like input as to it's > > nature. > > The code inside the system would already appear to support handling > > three elements, though it needs some scrutiny, > > so all that is needed is a system call with the ability to set the > > birthtime directly. > > Whether it should take the form of the existing calls but expecting > > three items is up for discussion. > > Maybe teh addition of a flags argument to specify which items are > > present and which to set. > > ideas? > I believe these should be new calls. Only utimensat() provides a flag > argument, but it is reserved for AT_* flags. I would be fine with > something like futimens3() and utimensat3() (where 3 means "three > timespecs"). Jilles implemented futimens() and utimensat(), so he > might have ideas as well. I would probably stick the birth time in > the third (final) timespec slot to make it easier to update new code > (you can use an #ifdef just around ts[2] without having to #ifdef the > entire block). Without adding new syscalls, it is possible to use the first tv_nsec to indicate that a new birth time is present. In that case, times[0].tv_nsec == UTIME_WITHBIRTHTIME would indicate that times has 4 instead of 2 elements. Whether you want to do this instead of adding two more system calls is a different question. Also note that, in some sense, the inability to set the birthtime forward is a feature. -- Jilles Tjoelker
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