Date: Sat, 26 Aug 2017 20:56:06 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: freebsd-hackers@freebsd.org Subject: Re: [PATCH] O_NOATIME support for open(2) Message-ID: <20170826175606.GQ1700@kib.kiev.ua> In-Reply-To: <20170826161827.GA21456@schoggimuss.roe.ch> References: <20170826161827.GA21456@schoggimuss.roe.ch>
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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. > > 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 ? > > 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.
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