Date: Wed, 18 Nov 2015 11:49:01 +0200 From: Daniel Braniss <danny@cs.huji.ac.il> To: Alfred Perlstein <alfred@freebsd.org> Cc: Rick Macklem <rmacklem@uoguelph.ca>, Konstantin Belousov <kostikbel@gmail.com>, hackers@freebsd.org Subject: Re: kqueue of a nfs mounted file not working Message-ID: <FCEAD57F-38BC-4CF4-B0CF-7CE0E9571ED1@cs.huji.ac.il> In-Reply-To: <564A8B6F.3080009@freebsd.org> 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>
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> On 17 Nov 2015, at 04:05, Alfred Perlstein <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>; > > 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. thanks, dannyhelp
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