On 06/16/2010 07:41 AM, Markus Armbruster wrote:
Kevin Wolf<kw...@redhat.com> writes:
Am 15.06.2010 15:44, schrieb Avi Kivity:
On 06/10/2010 08:45 PM, Markus Armbruster wrote:
* Our config file format is in INI syntax. QemuOpts correspond to
INI sections. Sections can't be nested, so recursive QemuOpts
don't translate.
git (and probably others) use
[a "b"]
c = d
for
a.b.c=d
Examples:
* Single protocol:
-blockdev id=blk1,format=raw,protocol=[file,file=fedora.img]
Requires suitable syntactic sugar to get the simple form (*).
* blkdebug
-blockdev id=blk2,format=qcow2,\
protocol=[blkdebug,config=test.blkdebug,\
protocol=[file,file=test.qcow2]]
* Avi's mirror:
-blockdev id=blk3,format=raw,\
protocol=[mirror,\
[file,file=local.img],\
[nbd,domain=unix,sockert=nbd-sock]]
2. We already have a syntax to specify trees, namely JSON, so use it
If -blockdev's argument starts with '{', it's a JSON object suitable
as argument of blockdev_add in QMP.
We still provide ordinary QemuOpts syntax for the cases that can be
expressed with it, i.e. single protocol.
I figure we'd want syntactic sugar for blkdebug, to permit its use
from the command line without having to resort to JSON.
Might be nice as a general extension to QemuOpts.
I agree.
3. Stack protocols through named references
The first protocol is "inlined" into -blockdev. Any further
protocols need to be referenced by name.
Best explained by example:
* Single protocol:
-blockdev id=blk1,format=raw,protocol=file,file=fedora.img
To get the simple form (*), make protocol optional with a suitable
default.
* blkdebug
-blockdev id=blk2,format=qcow2,protocol=blkdebug,config=test.blkdebug,\
base=blk2-base
-blockproto id=blk2-base,protocol=file,file=test.qcow2
* Avi's mirror:
-blockdev id=blk3,format=raw,protocol=mirror,\
base=blk3-base1,base=blk3=base2
-blockproto id=blk3-base1,protocol=file,file=local.img
-blockproto id=blk3-base2,protocol=nbd,domain=unix,sockert=nbd-sock
Anything but a single protocol becomes pretty verbose. Syntactic
sugar for the blkdebug case would be possible; not sure it's worth
it.
No QemuOpts syntax changes. INI can handle this just fine.
Looks like the least painful option as no new infrastructure is needed.
I'd go with this.
But it's painful to type for the user. After all -blockdev on the
command line is for the user, as tools should use QMP. Also note that
this syntax mixes format and protocol options on one line which I
consider confusing at best.
As I told Markus already in private before he posted this, I prefer the
bracket solution for its clarity and simplicity, even though it comes at
the cost of having additional characters that need to be escaped.
I dont't think 1. is less painful than 3. Let's compare the two:
* Single protocol: identical with suitable syntactical sugar, namely
-blockdev id=blk1,file=fedora.img
First, let me say that -blockdev is not something that I believe is
targeted at users. It's incredible unfair for us to expect a user to type:
-blockdev id=blk1,file=fedora.img -device ide-drive,drive=blk1,bus=0,unit=0
Instead of:
-hda fedora.img
I had to look up the device syntax just to write that. There's no way
users are going to do this. We should drop any notion of syntactical
sugar IMHO. -blockdev is for management tools, scripts, and as an
infrastructure for config files.
Unsugared it's
-blockdev id=blk1,format=raw,protocol=[file,file=fedora.img]
vs.
-blockdev id=blk1,format=raw,protocol=file,file=fedora.img
Specifying nesting in a single option is a bad idea. It should be:
-blockdev id=blk1,format=raw,protocol=blk2 \
-blockdev id=blk2,file=fedora.img
But honestly, I'm thoroughly confused about the distinction between
protocol and format. I had thought that protocols were a type of format
and I'm not sure why we're making a distinction.
I sure prefer the latter. The brackets look like noise. You need to
understand protocol stacking for them to make any sense.
Regarding confusion caused by mixing format and protocol options: yes,
the brackets force you to distinguish between protocol options and
other options. But I doubt that'll reduce confusion here. Either you
understand protocols. Then I doubt you need brackets to unconfuse
you. Or you don't understand protocols. Then whether to put an
option inside or outside the brackets is voodoo.
If the above is necessary just to create a raw image, then we're doing
something wrong in the block layer. If should be possible to just say:
-blockdev id=blk1,format=raw,file=fedora.img
Regards,
Anthony Liguori
