Date: Sun, 27 Aug 2017 15:18:06 +0200 From: Daniel Roethlisberger <daniel@roe.ch> To: freebsd-hackers@freebsd.org Subject: Re: [PATCH] O_NOATIME support for open(2) Message-ID: <20170827131806.GB21456@schoggimuss.roe.ch> In-Reply-To: <20170826175606.GQ1700@kib.kiev.ua> References: <20170826161827.GA21456@schoggimuss.roe.ch> <20170826175606.GQ1700@kib.kiev.ua>
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Konstantin Belousov <kostikbel@gmail.com> 2017-08-26: > On Sat, Aug 26, 2017 at 06:18:27PM +0200, Daniel Roethlisberger wrote: > > I'm trying to implement O_NOATIME support for open(2) in order to > > provide a more elegant way for backup/archiving software to > > prevent atime clobbering. Except for a 2008 thread on this list > > I did not find any material; not sure if anybody is interested in > > this or if there are reasons why this was never implemented. > Please point out the thread, e.g. by providing a link to the first > message in the thread in mailman archive. https://lists.freebsd.org/pipermail/freebsd-hackers/2008-October/thread.html#26531 https://lists.freebsd.org/pipermail/freebsd-hackers/2008-October/026531.html > > The attached patch against 11.1 implements O_NOATIME support for > > open(2); it prevents read(2) and mmap(2) from clobbering atime if > > the file descriptor was opened with O_NOATIME. O_NOATIME is only > > permitted for root and the owner of the file. Currently it is > > only implemented for ufs/ffs. It seems to work for me but has > > not been extensively tested. > What would happen when additional page-in occurs on the mmaped area ? With mmap, the vnode is marked for atime update at the time of calling mmap (unless O_NOATIME is set on the fd). I do not see how the patch would impact page-ins in any way. Can you elaborate? > > I am interested in feedback from people who know their way around > > I/O and VFS code before I extend this to other file systems, make > > O_NOATIME tunable by fcntl(2), wire it to the Linux compat layer > > and write docs. Does the implementation look sane? Did I miss > > something important? > > > > Specifically, is there a better way to pass O_NOATIME into > > vm_mmap_vnode other than adding an additional boolean_t argument? > > I did not use an additional mmap flag because that would have > > required additional logic to prevent userland from passing the > > flag to the mmap syscall. > If you need two booleans to the function, consider substituting the > arguments with the single u_int flags, and define two flags, one for > the writecounted, one for noatime. Thanks for the feedback, I appreciate it. Daniel -- Daniel Roethlisberger http://daniel.roe.ch/
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