Date: Wed, 28 May 2008 18:00:14 +0200 From: "Ivan Voras" <ivoras@freebsd.org> To: freebsd-hackers@freebsd.org, ivoras@freebsd.org Subject: Re: Impact of having a large number of open file descriptors Message-ID: <9bbcef730805280900i1195b5f4rb879d22e9e0319d9@mail.gmail.com> In-Reply-To: <200805281446.m4SEkojn099133@lurza.secnetix.de> References: <g1jjki$6lc$1@ger.gmane.org> <200805281446.m4SEkojn099133@lurza.secnetix.de>
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2008/5/28 Oliver Fromme <olli@lurza.secnetix.de>: > Ivan Voras wrote: > > Im thinking again of the old idea of implementing poor man's file > > replication system using kqueue to monitor changes on files. > > It would be cool to have a kernel interface so you could > attach to a mountpoint and receive a log of all activity > on that file system. That's similar to what DragonFly's > journaling feature does. /me agrees. > Unfortunately the kqueue interface isn't capable of doing > something like that ... So this is not an answer to your > question, I'm afraid. > > > One other question: do kqueue events "coalesce" in the sense that if N > > operations happen (like write()s), there can be < N events passed to the > > kqueue (NOTE_WRITE)? > > The manpage says: "Multiple events which trigger the filter > do not result in multiple kevents being placed on the kqueue; > instead, the filter will aggregate the events into a single > struct kevent." That's mildly unfortunate but I think you're right - it agrees with the statement from the kqueue paper: "Events will normally considered to be "level-triggered", as opposed to "edge-triggered"." > > While at it, will EVFILT_VNODE and NOTE_WRITE catch "additional" ways > > the file can be modified, meaning mmap()? > > A quick grep for NOTE_WRITE on the sys tree indicates that > it doesn't. I'm not 100% sure though. Also bad for some users.
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