From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH 5/9] KVM: Adds ability to signal userspace using a file-descriptor Date: Tue, 15 May 2007 17:22:49 +0100 Message-ID: <20070515162249.GA19238@infradead.org> References: <20070515031217.9382.44999.stgit@novell1.haskins.net> <20070515031536.9382.16826.stgit@novell1.haskins.net> <4649650E.2070102@qumranet.com> <464968D6.BA47.005A.0@novell.com> <4649A4E1.BA47.005A.0@novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Davide Libenzi To: Gregory Haskins Return-path: Content-Disposition: inline In-Reply-To: <4649A4E1.BA47.005A.0-Et1tbQHTxzrQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org On Tue, May 15, 2007 at 12:18:17PM -0400, Gregory Haskins wrote: > >>> On Tue, May 15, 2007 at 11:40 AM, in message > , Davide Libenzi > wrote: > > > > I don't know how critical is the path where you will be doing check. The > > eventfd_fget() is pretty fast, so if you're not looking at a performance > > critical path, I'd suggest that. Otherwise you can do an early > > eventfd_get, and keep the file*. If you have no the ways to know if the > > userspace disconnected, an atomic_read(&file- >f_count)==1 will tell you > > that you're the only owner of the file* (that is, userspace closed the > > eventfd descriptor). I'd give preference to the former option though. > > Thanks for the insight, Davide. It sounds like we can probably stay with the way I have it for now, and keep the file->f_count idea in our back pocket should a performance problem arise. accessing file->f_count is not allowed for drivers. It took us quite a bit of effort to clean up all users a while ago, and it turned out most of them were rather buggy. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/