Date: Wed, 18 Nov 2015 11:59:09 +0200 From: Daniel Braniss <danny@cs.huji.ac.il> To: Alfred Perlstein <alfred@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, Rick Macklem <rmacklem@uoguelph.ca>, hackers@freebsd.org Subject: Re: kqueue of a nfs mounted file not working Message-ID: <DEAA67D5-05B5-4358-893F-B3598D604BAF@cs.huji.ac.il> In-Reply-To: <FCEAD57F-38BC-4CF4-B0CF-7CE0E9571ED1@cs.huji.ac.il> References: <9BC3EFA2-945F-4C86-89F6-778873B58469@cs.huji.ac.il> <20151115152635.GB5854@kib.kiev.ua> <3AEC67FD-2E67-4EF9-9D46-818ABF3D8118@cs.huji.ac.il> <661673285.88370232.1447682409478.JavaMail.zimbra@uoguelph.ca> <564A8B6F.3080009@freebsd.org> <FCEAD57F-38BC-4CF4-B0CF-7CE0E9571ED1@cs.huji.ac.il>
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> On 18 Nov 2015, at 11:49, Daniel Braniss <danny@cs.huji.ac.il> wrote: > >> >> On 17 Nov 2015, at 04:05, Alfred Perlstein <alfred@freebsd.org <mailto:alfred@freebsd.org>> wrote: >> >> >> >> On 11/16/15 6:00 AM, Rick Macklem wrote: >>> Daniel Braniss wrote: >>>>> On 15 Nov 2015, at 17:26, Konstantin Belousov <kostikbel@gmail.com> wrote: >>>>> >>>>> On Sun, Nov 15, 2015 at 11:22:55AM +0200, Daniel Braniss wrote: >>>>>> HI, >>>>>> I???m writing a program to monitor a file using kqueue(2), if the file is >>>>>> local >>>>>> all is OK, but if the file is via a nfs mounted fs, it only works once. >>>>>> stat shows the file growing, but kevent is not triggered. >>>>> Does file grow due to local changes on the nfs client, or some other >>>>> client changes the file, while your client tries to get kevent >>>>> notifications ? >>>> it gets updated by a host which has the file as local, so yes, it gets >>>> updated >>>> by another client/host. >>>> >>> Hmm, I am not surprised that this doesn't work. The only indication to the >>> client that the file has changed on the server is a change in the file's >>> attributes when they're acquired (via a Getattr RPC or similar) from the server. >>> >>> There is a vfs operation called VFS_SYSCTL(). This isn't implemented on >>> the current NFS client. It was implemented on the old one, but only for >>> NFS locking events and I didn't understand what needed to be done, so I >>> didn't do it. >>> Kostik, do you know if there is a VFS_SYSCTL() call done when the kevent >>> stuff is probing for a file size change? (Or does it not probe and events >>> get triggered via the write syscall or ???) I took a quick look at the kevent >>> stuff, but admit I got lost and couldn't figure out what triggered events >>> being logged? >>> >>> Also, is the event for "file growing" or "file changed"? >>> If it is the latter, all the NFS client can do is look for a change in >>> the file's modify time and this is often at a resolution of 1sec., which >>> implies that a change within the same second as the previous one may not >>> be noticed. (NFSv4 has a Change attribute that is always guaranteed to >>> change, but that is only NFSv4.) Also, you see metadata changes as well >>> as data changes, at least for the NFSv4 attribute. >>> >>> rick >>> >> Hello Rick, >> >> I implemented the VFS_SYSCTL work in NFS. The goal was to allow a path to query filesystems via sysctl. >> >> This was used in OS X to provide a way to query the filesystem for "events". >> >> https://github.com/opensource-apple/xnu/blob/10.10/bsd/nfs/nfs_vfsops.c#L5188 <https://github.com/opensource-apple/xnu/blob/10.10/bsd/nfs/nfs_vfsops.c#L5188>; <https://github.com/opensource-apple/xnu/blob/10.10/bsd/nfs/nfs_vfsops.c#L5188 <https://github.com/opensource-apple/xnu/blob/10.10/bsd/nfs/nfs_vfsops.c#L5188>>; >> >> For NFS you want to inform the user that an nfs filesystem is down, or the locking daemon is down. That was inside a GUI you can pop up a dialog box to allow the user to force-unmount or turn off locking. >> >> Image you're connected to multiple NFS shares inside of X11 or whatever windowing system you have. Then there is a network outage. You'll want to know which filesystems are not responding and why. >> >> -Alfred >> >> -Alfred > > I found a workaround, not elegant, but works, > I added a timeout to the kevent instead of Null. > so now it’s working in busy wait mode instead of event driven. > I you plant add themishing links, I can heliport with the testing. > I hate spell checkers s/themishing/the missing links/ s/heliport/help out/ > thanks, > danny > > > _______________________________________________ > freebsd-hackers@freebsd.org <mailto:freebsd-hackers@freebsd.org> mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers <https://lists.freebsd.org/mailman/listinfo/freebsd-hackers>; > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org <mailto:freebsd-hackers-unsubscribe@freebsd.org>"help
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