From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sc8-sf-mx1-b.sourceforge.net ([10.3.1.11] helo=sc8-sf-mx1.sourceforge.net) by sc8-sf-list1.sourceforge.net with esmtp (Exim 4.30) id 1DXpnE-0007dP-4U for user-mode-linux-devel@lists.sourceforge.net; Mon, 16 May 2005 17:18:40 -0700 Received: from smtp005.mail.ukl.yahoo.com ([217.12.11.36]) by sc8-sf-mx1.sourceforge.net with smtp (Exim 4.41) id 1DXpmj-0007yl-8u for user-mode-linux-devel@lists.sourceforge.net; Mon, 16 May 2005 17:18:39 -0700 From: Blaisorblade Subject: Re: [uml-devel] Explaination of system call function flow in TT mode References: <003e01c503b3$f3e46cb0$ac655e0a@sha.st.com> <200505162324.37749.blaisorblade@yahoo.it> <3524bf1f0505161709476c4940@mail.gmail.com> In-Reply-To: <3524bf1f0505161709476c4940@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200505170217.23138.blaisorblade@yahoo.it> Sender: user-mode-linux-devel-admin@lists.sourceforge.net Errors-To: user-mode-linux-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Id: The user-mode Linux development list List-Post: List-Help: List-Subscribe: , List-Archive: Date: Tue, 17 May 2005 02:17:22 +0200 To: user-mode-linux-devel@lists.sourceforge.net, Young Koh On Tuesday 17 May 2005 02:09, Young Koh wrote: > Ok, now i'm getting close. Thanks a lot!!! > but i have two more :) > > 1) in SKAS mode, the tracer (UML kernel) will execute a system call > for the tracee (the user process). But what if the system call blocks? > then, the tracer, the UML kernel, will be blocked, too, right? it > means the whole UML system will be blocked? Good question. However the tracee is one of the threads running inside UML, i.e. switch_to_skas switches between the different tracees. However, that's done only on timer interrupts, and possibly those interrupts are blocked by the syscall execution. Indeed, I remember that when the UBD I/O is run by the UML kernel and not by a separate thread (this has been removed) the whole system becomes *really* slow, so probably the answer to your question is "Yes, but UML tries to avoid this". > 2) in TT mode, what if the user process (tracee) installs its own > signal handler for SIGUSR2? The syscall is intercepted so it can't install signal handlers; the one it installs are handled inside the UML kernel. -- Paolo Giarrusso, aka Blaisorblade Skype user "PaoloGiarrusso" Linux registered user n. 292729 http://www.user-mode-linux.org/~blaisorblade ------------------------------------------------------- This SF.Net email is sponsored by Oracle Space Sweepstakes Want to be the first software developer in space? Enter now for the Oracle Space Sweepstakes! http://ads.osdn.com/?ad_id=7412&alloc_id=16344&op=click _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel