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Re: [Qemu-devel] [PATCH 04/14] qdev: take ownership of id pointer

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH 04/14] qdev: take ownership of id pointer
Date: Tue, 20 Sep 2011 08:55:47 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110516 Lightning/1.0b2 Thunderbird/3.1.10

On 09/20/2011 08:21 AM, Gerd Hoffmann wrote:
On 09/20/11 15:04, Anthony Liguori wrote:
On 09/20/2011 01:36 AM, Gerd Hoffmann wrote:
On 09/19/11 18:27, Anthony Liguori wrote:
On 09/19/2011 02:34 AM, Gerd Hoffmann wrote:
FYI: Keeping the pointer to the QemuOpts has one more reason: It will
free the
QemuOpts on hot-unplug, which is needed to free the id from QemuOpts
point of
view, which in turn allows to re-use the id when hot-plugging the same
another) device later on.

You mean, tie QemuOpts life cycle to devices life cycle


such that you
cannot accidentally create a non-device QemuOpts that conflicts with the
id of a device?

Device QemuOpts have their own id namespace, so this is just about
within devices. This ...

device_add e1000,id=nic1
device_del nic1
device_add e1000,id=nic1

... will work only if you free the QemuOpts when deleting a device,
QemuOpts will complain that nic1 is used already.

But we can just verify that the id specified for qdev is unique at
creation time and fail creation if it isn't, no?

Since not all devices are assigned names via qemuopts, that seems like a
safer approach anyway.

I think that happens anyway (didn't check the source though).

Problem is that QemuOpts wants IDs being unique too, so keep the QemuOpts
hanging around instead of releasing them makes QemuOpts complain about nic1 not
being unique although there isn't such a device in qdev space.

I don't think we have a firm requirement that the QemuOpts namespace == device namespace. At any rate, it's not enforced today because devices can be created (with an id) outside of device_add.

Oh, and not
releasing the QemuOpts would also leak memory on each hot-unplug.

If you look at my patch, opts is freed at the end of device_add so there is no 


Anthony Liguori


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