From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:58242) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qov9A-0007u7-2W for qemu-devel@nongnu.org; Thu, 04 Aug 2011 06:27:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Qov98-0001We-P2 for qemu-devel@nongnu.org; Thu, 04 Aug 2011 06:27:24 -0400 Received: from david.siemens.de ([192.35.17.14]:20602) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qov98-0001WW-Bp for qemu-devel@nongnu.org; Thu, 04 Aug 2011 06:27:22 -0400 Message-ID: <4E3A7408.5030300@siemens.com> Date: Thu, 04 Aug 2011 12:27:20 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <1312384643-581-1-git-send-email-lcapitulino@redhat.com> <1312384643-581-3-git-send-email-lcapitulino@redhat.com> <4E3A6C8C.8060304@redhat.com> <4E3A71D3.6030700@siemens.com> In-Reply-To: <4E3A71D3.6030700@siemens.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 2/7] Replace VMSTOP macros with a proper QemuState type List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: blauwirbel@gmail.com, amit.shah@redhat.com, aliguori@us.ibm.com, qemu-devel@nongnu.org, Luiz Capitulino On 2011-08-04 12:17, Jan Kiszka wrote: > On 2011-08-04 11:55, Avi Kivity wrote: >> On 08/03/2011 06:17 PM, Luiz Capitulino wrote: >>> @@ -9,6 +9,20 @@ >>> #include "notify.h" >>> >>> /* vl.c */ >>> + >>> +typedef enum { >>> + QSTATE_DEBUG, /* qemu is running under gdb */ >>> + QSTATE_INTERROR, /* paused due to an internal error */ >>> + QSTATE_IOERROR, /* paused due to an I/O error */ >>> + QSTATE_PAUSED, /* paused by the user (ie. the 'stop' >>> command) */ >>> + QSTATE_PREMIGRATE, /* paused preparing to finish migrate */ >>> + QSTATE_RESTVM, /* paused restoring the VM state */ >>> + QSTATE_RUNNING, /* qemu is running */ >>> + QSTATE_SAVEVM, /* paused saving VM state */ >>> + QSTATE_SHUTDOWN, /* guest shut down and -no-shutdown is in >>> use */ >>> + QSTATE_WATCHDOG /* watchdog fired and qemu is configured to >>> pause */ >>> +} QemuState; >>> + >>> extern const char *bios_name; >>> >> >> Why "QemuState"? In general, "qemu" can be inferred from the fact that >> we're in qemu.git. Suggest "RunState". >> >> Second, these states can coexist. A user may pause the VM >> simultaneously with the watchdog firing or entering premigrate state. >> In fact, with multiple monitors, each monitor can pause and resume the >> vm independently. >> >> So I think we should keep a reference count instead of just a start/stop >> state. Perhaps >> >> vm_stop(QemuState s) >> { >> ++stopcount[s]; >> } >> >> vm_is_stopped() >> { >> for (s in states) >> if (stopcount[s]) >> return true; >> return false; >> } > > I don't think this makes sense nor is user-friendly. If one command > channel suspends the machine, others have the chance to subscribe for > that event. Maintaining a suspension counter would mean you also need a > channel to query its value. > > IMHO, there is also no use for defining stopped orthogonally to > premigrate and other states that imply that the machine is stopped. > Basically they mean "stopped for/because of X". We just need to avoid > that you can enter plain stopped state from them by issuing the > corresponding monitor command. The other way around might be possible, > though, if there are race windows. The makes me wonder if qemu_state_set shouldn't validate if the state transition is legal (simple switch/case). That way, we would have a central point and could also avoid potential races or logical bugs where a newly set state is accidentally overwritten due to unexpected execution order. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux