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Re: [Qemu-devel] [PATCH 1/5] block: Auto-generate node_names for each BD

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH 1/5] block: Auto-generate node_names for each BDS entry
Date: Thu, 15 May 2014 09:59:01 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0

On 05/14/2014 09:20 PM, Jeff Cody wrote:
> Currently, node_name is only filled in when done so explicitly by the
> user.  If no node_name is specified, then the node name field is not
> populated.
> If node_names are automatically generated when not specified, that means
> that all block job operations can be done by reference to the unique
> node_name field.  This eliminates ambiguity in filename pathing
> (relative filenames, or file descriptors, symlinks, mounts, etc..) that
> qemu currently needs to deal with.
> If a node name is specified, then it will not be automatically
> generated for that BDS entry.
> If it is automatically generated, it will be prefaced with "__qemu##",
> followed by 8 characters of a unique number, followed by 8 random
> ASCII characters in the range of 'A-Z'.  Some sample generated node-name
> strings:
>     __qemu##00000000IAIYNXXR
>     __qemu##00000002METXTRBQ
>     __qemu##00000001FMBORDWG
> The prefix is to aid in identifying it as a qemu-generated name, the
> numeric portion is to guarantee uniqueness in a given qemu session, and
> the random characters are to further avoid any accidental collisions
> with user-specified node-names.
> Signed-off-by: Jeff Cody <address@hidden>
> ---
>  block.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)

This patch feels incomplete.  We probably also ought to modify
qapi-schema.json to make BlockDeviceInfo's output of 'node-name' by
unconditional (as an output-only struct, changing from optional to
mandatory is a safe change for back-compat API considerations); which
implies further modifying code to get rid of has_node_name arguments in
all places that generate BlockDeviceInfo details.

See also my thoughts on patch 5/5 - can this patch be rebased to be LAST
in the series, rather than first, so that it serves as a reliable
witness that everything else related to block operations on node-names
is complete?

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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