Date: Thu, 31 Mar 2005 01:32:13 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Matthew Luckie <mjl@luckie.org.nz> Cc: freebsd-hackers@freebsd.org Subject: Re: kqueue and ordinary files Message-ID: <20050331073213.GE46288@dan.emsphone.com> In-Reply-To: <424BA0B5.2000302@luckie.org.nz> References: <424BA0B5.2000302@luckie.org.nz>
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In the last episode (Mar 31), Matthew Luckie said: > Does kqueue signal EOF on an ordinary file when there is nothing left > to read? > > The code at http://www.wand.net.nz/~mjl12/kqfile.c.txt > > cc -Wall -o kqfile kqfile.c > ./kqfile kqueue.c > > doesn't ever get EOF notification as far as i can tell. as in, it > isn't signaled in kevent.flags, nor does kqueue signal the file is > ready for reading and then read(2) return 0. > > ident 3 filter 0xffffffff flags 0x0001 fflags 0x0000 data 128 > read 128 bytes > > how should i detect that the file no longer has anything left to read > with kqueue? at the moment I use select but would like to use kqueue > where available. You can get it indirectly by examining the data field. You can see that the call just before the final kqueue returns data=60, so if your read call returns 60, you're done. The current behaviour is useful for things like tail or syslog watchers, so that they get an EVFILT_READ event when the file grows. They may be better off registering an EVFILT_VNODE/NOTE_EXTEND event though, so you could make a case for returning EV_EOF on EVFILT_READ instead of blocking. -- Dan Nelson dnelson@allantgroup.com
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