Re: [PATCH v1 1/7] xen-block: Do not write frontend nodes

From: David Woodhouse <dwmw2@infradead.org>
To: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Cc: Oleksandr Tyshchenko <Oleksandr_Tyshchenko@epam.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Anthony Perard <anthony.perard@citrix.com>,
	Paul Durrant <paul@xen.org>, Kevin Wolf <kwolf@redhat.com>,
	Hanna Reitz <hreitz@redhat.com>,
	"open list:X86 Xen CPUs" <xen-devel@lists.xenproject.org>,
	"open list:Block layer core" <qemu-block@nongnu.org>
Subject: Re: [PATCH v1 1/7] xen-block: Do not write frontend nodes
Date: Sat, 11 Nov 2023 10:55:49 +0000	[thread overview]
Message-ID: <f2f7751a9ea5597e9f7a1417b761fe0802892aa8.camel@infradead.org> (raw)
In-Reply-To: <20231110204207.2927514-2-volodymyr_babchuk@epam.com>

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On Fri, 2023-11-10 at 20:42 +0000, Volodymyr Babchuk wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> 
> The PV backend running in other than Dom0 domain (non toolstack domain)
> is not allowed to write frontend nodes. The more, the backend does not
> need to do that at all, this is purely toolstack/xl devd business.
> 
> I do not know for what reason the backend does that here, this is not really
> needed, probably it is just a leftover and all xen_device_frontend_printf()
> instances should go away completely.

No, this is what allows qemu to create PV devices, as opposed to just
handle the ones which are created for it by the toolstack.

Perhaps we should only create the frontend nodes (and likewise, only
destroy those and the backend nodes on destruction) in the case where
the device was instantiated directly by the QEMU command line, and
refrain from doing so for the devices which were created by the
toolstack and merely 'discovered' by xen_block_device_create()?

(Note that we need to look at net and console devices too, now they've
finally been converted to the 'new' XenBus framework in QEMU 8.2.)

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