On Mon, Feb 28, 2011 at 3:48 PM, Kevin Wolf <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> 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?)
Yes, I think you're right. We should aim for a general interface rather than having to add many more specific interfaces in the future. CQ: Do you see a relation to the "update" interface you added to adjust drive options at runtime for FVD? Stefan
