From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.33) id 1BUler-0007hG-PZ for qemu-devel@nongnu.org; Mon, 31 May 2004 08:12:50 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.33) id 1BUlej-0007fF-Jc for qemu-devel@nongnu.org; Mon, 31 May 2004 08:12:46 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.33) id 1BUlej-0007ex-8k for qemu-devel@nongnu.org; Mon, 31 May 2004 08:12:41 -0400 Received: from [81.209.184.159] (helo=dd2718.kasserver.com) by monty-python.gnu.org with esmtp (Exim 4.34) id 1BUldT-0003rg-CG for qemu-devel@nongnu.org; Mon, 31 May 2004 08:11:23 -0400 Message-ID: <40BB20E6.6010307@fabianowski.de> Date: Mon, 31 May 2004 14:11:18 +0200 From: Bartosz Fabianowski MIME-Version: 1.0 Subject: Re: [Qemu-devel] Changing RTC from UTC to local time References: <40B8A0B1.3040601@fabianowski.de> <20040530215949.GB5521@lebarbe.net> <40BA7C79.1070703@fabianowski.de> <200405301852.25158.kyle@silverbeach.net> In-Reply-To: <200405301852.25158.kyle@silverbeach.net> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: kyle@silverbeach.net, qemu-devel@nongnu.org > So, you should probably _always_ have the emulated OS keep away from > the RTC. The host OS will provide the correct time as the fake RTC > value. My point exactly. Your host operating system is most likely one you use quite a lot so chances are you will have set it up correctly to take care of DST adjustments. When installing a slave OS that requires a local RTC (Windows), you can just tell it the RTC is local and also tell it to keep away from the RTC. When the host adjusts for DST, the slave will automatically follow - theoretically, this should work even if it occurs while QEMU is running. Though I haven't tried this yet. And as a further safeguard, as I pointed out earlier, QEMU will always reset the RTC if the slave OS starts tinkering with it. So even if you forget to tell your slave OS to stop setting the RTC, no harm is done. > Actually, while installing SuSE 9.1 yesterday, I noted that it states > that the clock should be set to UTC unless you are dual booting. I have never installed Linux on a machine myself so I didn't know what Linux recommends. From your post and my own experience I conclude once again that both Linux and *BSD can deal with a local time RTC while Windows actually requires one. So if your RTC is running in local time, all of those OSes will work. However, when your RTC is UTC, only Linux and *BSD will work correctly. Windows will give you the wrong time. This is why I believe we should have: a) a choice between UTC and local time and b) a safe default that makes all OSes work - which is local time I guess it breaks down to this: If you are tinkering with Linux or *BSD inside QEMU, you want your RTC to be UTC, as that is technically the better way of doing it and it works nicely. If you are installing Windows however, you want local time. Judging from the current posts on the mailing list, the number of people who install Windows for now seems to be smaller than that of people who install Linux or *BSD. But I could well imagine that once QEMU matures and the word gets out, people will start using it as a VMWare replacement for when they need that lonely Windows application and Wine just won't do. Which happens to be the situation I am in. So in anticipation of such a use - a use by newbies - I believe a safe default is very important. Thus, again, I believe my patch should be committed. But that, after all, is Fabrice's choice. - Bartosz