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Re: [Qemu-devel] [Qemu-block] [RFC PATCH 0/7] BlockBackends, nodes and g
Re: [Qemu-devel] [Qemu-block] [RFC PATCH 0/7] BlockBackends, nodes and guest devices
Mon, 11 Jul 2016 20:13:18 -0400
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1
No oxford comma in the subject? :)
On 06/23/2016 10:36 AM, Kevin Wolf wrote:
> I am relatively confident to say that everything that should use a
> BlockBackend, does so by now. Almost all users create their own anonymous
> BlockBackend internally and use that. The user configures the BB only
> indirectly using the configuration methods of the user that the BB belongs to.
> There is one exception, which are guest devices. There the user is expected to
> manually set up a BlockBackend and pass it to the device. This requires that
> users understand the difference between node and BlockBackends and manage both
> kinds of objects. This is a rather nasty interface.
> My goal is that we allow a user (management tool) to ignore that BlockBackends
> exist as separate entities in qemu. Ideally we could fully make them an
> implementation detail, but I'm not sure to which degree we can do that for
> compatibility reasons. But what I'm pretty sure we can do is provide
> that address everything using either node names or (qdev) device names, so
> you don't have to manage BlockBackends if you don't want to.
> This involves several steps, and for most of them this series contains an
> example patch that shows what this could look like:
> 1. Accept node-name in -device drive=... and create an internal anonymous BB
> for devices configured this way. This is the way to create devices that
> completely avoid legacy interfaces using the BB name.
> 2. Update all QMP commands touching block devices. There are two kinds of
> concerning either the guest device (which the BlockBackend is logically
> of, even though it's not implemented this way) or the actual backend
> (BlockDriverState/node level)
> * Device level commands: Accept a guest device ID instead of BB name to
> identify the BlockBackend the command works on. As device IDs and BB
> don't share a single namespace, we'll need a new QMP argument for this.
> * Node level commands: We need to complete the conversion that makes
> commands accept node names instead of BlockBackend names. In some places
> we intentionally allow only BlockBackends because we don't know if the
> command works in other places than the root. This is okay, but we can
> accept node names anyway. We just need to check that the node is a root
> node as expected.
> 3. Remove all BlockBackend options from blockdev-add. This has already
> partially (e.g. WCE flag), but at least id, rerror, werror are still there.
> This is a very incompatible change, but we declared blockdev-add
> experimental, so I think it's acceptable.
> 4. Add BlockBackend options as qdev properties to all block devices.
> 5. Add a way on the command line to create block nodes that have a node-name
> and don't have a BlockBackend. blockdev-add already supports this (and
> implementing 3. it will be the only mode supported by blockdev-add), but we
> can't do this on the command line yet. You always get a BB with -drive.
> This might finally become the -blockdev we were talking about at the very
> beginning of the block layer generalisation work.
> So this is my plan. It's pretty radical, but I think we really must do
> something about our interfaces. Having nodes, BlockBackends and guest devices
> to manage is just too much and doesn't really make sense. Making BlockBackends
> visible in the external API essentially only as aliases for either node names
> or guest devices (and that only for compatibility, not when using
> -blockdev) feels to me like the right thing to do.
> But of course I'm aware that there probably isn't a clear right or wrong, and
> that I might be missing important details, so this needs to be discussed in
> advance before I go and implement the full thing instead of just small example
> So please let me know what you guys think about this plan.
> Kevin Wolf (7):
> block/qdev: Allow node name for drive properties
> block: Add blk_by_dev()
> qdev-monitor: Factor out find_device_state()
> qdev-monitor: Add blk_by_qdev_id()
> block: Accept device model name for blockdev-open/close-tray
> block: Accept node-name for block-stream
> block/qdev: Allow configuring WCE with qdev properties
> block/block-backend.c | 19 +++++++++
> blockdev.c | 92
> hw/block/block.c | 16 +++++++
> hw/block/nvme.c | 1 +
> hw/block/virtio-blk.c | 1 +
> hw/core/qdev-properties-system.c | 18 +++++++-
> hw/ide/qdev.c | 1 +
> hw/scsi/scsi-disk.c | 1 +
> hw/usb/dev-storage.c | 1 +
> include/hw/block/block.h | 5 ++-
> include/sysemu/block-backend.h | 2 +
> qapi/block-core.json | 16 ++++---
> qdev-monitor.c | 34 +++++++++++++--
> qmp-commands.hx | 14 +++---
> 14 files changed, 178 insertions(+), 43 deletions(-)
1-4: Reviewed-by: John Snow <address@hidden>
5: Looks good, pending discussion on the right thing to name "ID", but
the patch itself looks perfectly cromulent.
6: Causes only a minor regression in 030 due to different error class
names, but R-B otherwise.
7: No opinion. Looks sane mechanically but I don't know enough about
core block properties to have a meaningful opinion. "ACK."
For non-RFC, some new iotests would be good.
- Re: [Qemu-devel] [Qemu-block] [RFC PATCH 0/7] BlockBackends, nodes and guest devices,
John Snow <=