From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:45421) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ROAVy-0003Cs-L4 for qemu-devel@nongnu.org; Wed, 09 Nov 2011 10:56:40 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ROAVx-00037d-7c for qemu-devel@nongnu.org; Wed, 09 Nov 2011 10:56:38 -0500 Received: from mx1.redhat.com ([209.132.183.28]:15495) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ROAVw-00037W-SQ for qemu-devel@nongnu.org; Wed, 09 Nov 2011 10:56:37 -0500 Message-ID: <4EBAA2AE.5070003@redhat.com> Date: Wed, 09 Nov 2011 17:56:30 +0200 From: Avi Kivity MIME-Version: 1.0 References: <1319540983-4248-1-git-send-email-benoit.canet@gmail.com> <1319540983-4248-5-git-send-email-benoit.canet@gmail.com> <4EB8CD52.1000008@redhat.com> <4EB91EDE.7070909@redhat.com> <4EB922DD.6040309@redhat.com> <4EB933BE.7080503@codemonkey.ws> <4EB93ED9.6060105@redhat.com> <4EB944EE.9090304@codemonkey.ws> <4EB9477D.5010804@redhat.com> <4EB94B9F.5040102@codemonkey.ws> <4EB964AC.6000605@redhat.com> <4EBA90D8.8040707@codemonkey.ws> <4EBA96BD.5050904@redhat.com> <4EBAA0EC.6030409@codemonkey.ws> In-Reply-To: <4EBAA0EC.6030409@codemonkey.ws> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 4/5] integratorcp: convert integratorcm to VMState List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Peter Maydell , =?UTF-8?B?QmVub8OudCBDYW5ldA==?= , qemu-devel@nongnu.org, quintela@redhat.com On 11/09/2011 05:49 PM, Anthony Liguori wrote: > >>> VMSTATE_MEMORY_REGION(integratorcm, flash), >> >> Therefore this line is 100% redundant. > > > Yes, but the problem is that it's not obvious *why*. That's what I'm > trying to get at here. If you have a VMSTATE_MEMORY_REGION() that has > all of it's fields marked immutable and one field marked derived, now > it becomes obvious *why* we don't save these fields. Every MemoryRegion field in qemu today is either immutable or slaved to another register. We could have a system to annotate every field, but it's pointless. If we had a device that set the region offset to some value it computes at runtime that is not derived from state (say, offset = count of writes to some register) then there would be some point in it. But we don't, so there isn't. > Just not having it in the vmstate description makes it very > non-obvious. Is it a bug? Is there some field in memory region that > I'm responsible for setting in a post load hook? Missing post-load hook bugs are not destructive. Of course we should try to avoid them, but a markup system that we know ends up doing nothing is excessive. > >>> This gives us a few things. First, it means we're describing how to >>> marshal everything which I really believe is the direction we need to >>> go. Second, it makes writing VMState descriptions easier to review. >>> Every field should be in the VMState description. Any field that is >>> in the derived_fields array should have its value set in the post_load >>> function. You could also have an immutable_fields array to indicate >>> which fields are immutable. >> >> 100% of the memory API's fields are either immutable or derived. > > Ok, let's at least make the code make it obvious that that is the case. The memory/mutators branch simplifies it by eliminating pseudo state like flash_mapped. > >>> BTW, I've thought about this in the past but never came up with >>> anything that really made sense. Have you thought about what what a >>> Register class would do? >>> >> >> name (for the monitor) >> size >> ptr to storage (in device state) >> writeable bits mask >> clear-on-read mask > > Really? Is that all that common outside of PCI config? Yes, ISR fields often have it (like virtio). > >> read function (if computed on demand; otherwise satisfied from storage) >> write function (if have side effects) > > I tried something like this in Python at one point and the code ended > up very big to write a device model. It's hard to beat the > conciseness of the dispatch functions with a switch() statement. This style of code really wants lambdas. Without them, we have 4-5 lines of boilerplate for each callback. Even then, it's worthwhile IMO (and many callbacks can be avoided, both read and write, or merged into a device_update_mapping or device_update_irq read-all-state style functions). -- error compiling committee.c: too many arguments to function