Am 01.03.2011 14:03, schrieb Anthony Liguori: > > On Feb 28, 2011 10:48 AM, "Kevin Wolf" <kw...@redhat.com > <mailto:kw...@redhat.com>> wrote: >> >> Am 28.02.2011 16:35, schrieb Stefan Hajnoczi: >> > On Mon, Feb 28, 2011 at 3:12 PM, Kevin Wolf <kw...@redhat.com > <mailto:kw...@redhat.com>> wrote: >> >> Am 28.02.2011 12:49, schrieb Prerna Saxena: >> >>> The following patchset introduces monitor commands: >> >>> >> >>> 1. set_cache DEVICE CACHE-SETTING >> >>> Change cache settings for block device, DEVICE, through the monitor. >> >>> (Available options : 'none', 'writeback', 'writethrough') >> >>> Eg, >> >>> (qemu)set_cache ide0-hd0 none >> >>> -> Changes cache setting for ide0-hd0 to 'none' >> >> >> >> Not sure if adding this interface is a good idea. I see that you only >> >> add it for HMP, and we may consider that, but it's definitely not >> >> suitable for QMP. >> >> >> >> One reason is that none/writethrough/writeback/unsafe isn't really what >> >> we want to use long term. We want to separate advertising a write cache >> >> (which is guest visible) from things like whether to use O_DIRECT > or not. >> >> >> >> In the past, Christoph mentioned that he had patches to make these >> >> separate and even let the guest change the "write cache enabled" flag, >> >> which would probably solve most of the use cases of this patch. >> > >> > Toggling host page cache at runtime is useful too because it saves >> > having to restart VMs. >> >> Not sure why I wanted to change that during runtime, but agreed, >> allowing to change parameters using the monitor is generally a good thing. >> >> However, I'm not sure if a command for changing the cache mode is the >> right solution, or if it should be something like a command to change >> block device options. (For example, what about toggling read-only or >> snapshot mode?) > > Certainly good questions, but let me suggest not taking an HMP command > and not a QMP commans because of interface concerns. > > My goal for 0.15 is to convert HMP to be implemented in terms of QMP. > To do that, a bunch of new QMP commands are needed. They all won't be > perfect but i'd rather support a bad QMP command forever than to > continue to/ have people rely on HMP.
Okay, makes sense. So we should reject patches that add new HMP commands without adding a QMP counterpart. >> > I agree that the guest should control the >> > emulated drive cache at runtime and we probably don't want to allow >> > toggling that from the host - it could be dangerous :). >> >> Good point. That's a NACK for this patch as long as we haven't separated >> WCE from the host cache setting. Doesn't make a difference for this one, though, because it's NACKed anyway. Kevin PS: Anthony, is there a specific reason why you started sending HTML emails?
