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Re: [Qemu-block] [PATCH v3 08/14] blockdev: Remove blk_hide_on_behalf_of

From: Kevin Wolf
Subject: Re: [Qemu-block] [PATCH v3 08/14] blockdev: Remove blk_hide_on_behalf_of_hmp_drive_del()
Date: Wed, 17 Feb 2016 15:18:35 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

Am 16.02.2016 um 19:08 hat Max Reitz geschrieben:
> This function first removed the BlockBackend from the blk_backends list
> and cleared its name so it would no longer be found by blk_name(); since
> blk_next() now iterates through monitor_block_backends (which the BB is
> removed from in hmp_drive_del()), this is no longer necessary.

Not clearing the name any more means that you can't create a new
BlockBackend with the same ID until the hidden BB finally goes away.

As it happens, you already can't do that with drive_add, because we also
keep the ID reserved in the QemuOpts, so it's already broken today.
However, before this patch, you can still use blockdev-add to create a
new BB with the ID of a BB that drive_del removed; after it, you get an

{"error": {"class": "GenericError", "desc": "Device with id 'disk'
already exists"}}

In order to fix this, I suggested on IRC that we view the BB name as
belonging to the monitor reference logically, i.e. we add a name with
monitor_add_blk() (which would get a new ID parameter) and clear it
again in monitor_remove_blk().

> Second, bdrv_make_anon() was called on the BDS. This was intended for
> cases where the BDS was owned by that BB alone; in which case the BDS
> will no longer exist at this point thanks to the blk_remove_bs() in
> hmp_drive_del().
> Therefore, this function does nothing useful anymore. Remove it.
> Signed-off-by: Max Reitz <address@hidden>


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