Date: Thu, 21 Jan 2016 20:13:08 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: "Batutis, Ed" <Ed.Batutis@netapp.com> Cc: Joerg Sonnenberger <joerg@britannica.bec.de>, Diane Bruce <db@db.net>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: get number of open files in a process? Message-ID: <20160121191308.GA21869@dft-labs.eu> In-Reply-To: <d26cc2fcea304ea6a89f61c2ec497322@hioexcmbx08-prd.hq.netapp.com> References: <ea9f2ab2d4f543c8ad34fdeb082f8c7a@hioexcmbx08-prd.hq.netapp.com> <20160121153636.GA10961@britannica.bec.de> <20160121161637.GA83843@night.db.net> <20160121162527.GA11600@britannica.bec.de> <d26cc2fcea304ea6a89f61c2ec497322@hioexcmbx08-prd.hq.netapp.com>
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On Thu, Jan 21, 2016 at 06:39:44PM +0000, Batutis, Ed wrote: > > > > Use getdtablesize() to get the current largest known fd. If you > > > > want, you can afterwards loop and use fcntl with F_GETFD to check if > > > > the descriptor is still open. > > Since I need an open handle count I would have to do 2048 fcntl() calls in my case. I'm afraid this doesn't look like a good idea, since it might happen a lot under certain circumstances. > > Looking at the source for kinfo_getfile, it seems like using this is not a good idea because, according to a comment in bug 197695: > > https://www.mail-archive.com/freebsd-bugs@freebsd.org/msg21569.html > > the function uses a sysctl with KERN_PROC_FILEDESC which "might be slow". This function also does two memory allocations for data I don't need to look at. > > So, I guess the answer is, for me anyway, that there is no sufficiently efficient way to get the number of open file handles from the system for my user-space application. > > But, if anyone has any more ideas, I'd be happy to hear them! > Well, OpenBSD has getdtablecount syscall giving a cheap way to obtain this information. FreeBSD gained a sysctl providing an equivalent functionality for compatiblity reasons, but the feature is only in head. https://svnweb.freebsd.org/base/head/sys/kern/kern_descrip.c?r1=287540&r2=290473 It is trivial to backport to 10.x, but I have no plans doing so (I'm not going to prevent anyone from doing it either). However, the real question is what do you need this for. -- Mateusz Guzik <mjguzik gmail.com>
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