Date: Sun, 9 Nov 2025 00:52:38 -0800 From: Rick Macklem <rick.macklem@gmail.com> To: Ronald Klop <ronald-lists@klop.ws> Cc: "Peter 'PMc' Much" <pmc@citylink.dinoex.sub.org>, FreeBSD CURRENT <freebsd-current@freebsd.org> Subject: Re: RFC: Should copy_file_range(2) return after a few seconds? Message-ID: <CAM5tNy6-=BqcwpsC==QemJua70taAYFYB0=4P3LaO53TKoiy8Q@mail.gmail.com> In-Reply-To: <2100145914.14642.1762672441817@localhost> References: <CAM5tNy4cpC0a_Bgngi_wJt_h_FwoVnDT5c3ozr7b4O_M0Kx5pA@mail.gmail.com> <2100145914.14642.1762672441817@localhost>
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On Sat, Nov 8, 2025 at 11:14 PM Ronald Klop <ronald-lists@klop.ws> wrote: > > > Van: Rick Macklem <rick.macklem@gmail.com> > Datum: 9 november 2025 00:23 > Aan: FreeBSD CURRENT <freebsd-current@freebsd.org> > CC: Peter 'PMc' Much <pmc@citylink.dinoex.sub.org> > Onderwerp: RFC: Should copy_file_range(2) return after a few seconds? > > Hi, > > Peter Much reported a problem on the freebsd-fs@ mailing > list on Oct. 21 under the Subject: "Why does rangelock_enqueue() > hang for hours?". > > The problem was that he had a copy_file_range(2) copying > between a large NFS file and a local file that was taking 2hrs. > While this copy_file_range(2) was in progress, it was holding > a rangelock for the entire output file, causing another process > trying to read the output file to hang, waiting for the rangelock. > > Since copy_file_range(2) is not any standard (just trying to > emulate the Linux one), there is no definitive answer w.r.t. > should it hold rangelocks. However, that is how it is currently > coded and I, personally, think it is appropriate to do so. > > Having a copy_file_range(2) syscall take two hours is > definitely an unusual case, but it does seem that it is > excessive? > > Peter tried a quick patch I gave him that limited the > copy_file_range(2) to 1sec and it fixed the problem > he was observing. > > Which brings me to the question... > Should copy_file_range(2) be time limited? > And, if the answer to this is "yes", how long do > you think the time limit should be? > (1sec, 2-5sec or ??) > > Note that the longer you allow copy_file_range(2) > to continue, the more efficient it will be. > > Thanks in advance for any comments, rick > > ________________________________ > > > > Why is this locking needed? > AFAIK Unix has advisory locking, so if you read a file somebody else is writing the result is your own problem. It is up to the applications to adhere to the locking. > Is this a lock different than file locking from user space? Yes. A rangelock is used for a byte range during a read(2) or write(2) to ensure that they are serialized. This is a POSIX requirement. (See this post by kib@ in the original email discussion. https://lists.freebsd.org/archives/freebsd-fs/2025-October/004704.html) Since there is no POSIX standard for copy_file_range(), it could be argued that range locking isn't required for copy_file_range(), but that makes it inconsistent with read(2)/write(2) behaviour. (I, personally, am more comfortable with a return after N sec than removing the range locking, but that's just my opinion.) rick > Why can’t this tail a file that is being written by copy_file_range if none of the applications request a lock? > > Regards, > Ronald. >help
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