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Re: [PATCH v3 2/4] bitmap: Enforce maximum bitmap name length

From: Eric Blake
Subject: Re: [PATCH v3 2/4] bitmap: Enforce maximum bitmap name length
Date: Fri, 15 Nov 2019 10:33:15 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1

On 11/15/19 9:47 AM, Vladimir Sementsov-Ogievskiy wrote:
15.11.2019 18:03, Vladimir Sementsov-Ogievskiy wrote:
14.11.2019 5:46, Eric Blake wrote:
We document that for qcow2 persistent bitmaps, the name cannot exceed
1023 bytes.  It is inconsistent if transient bitmaps do not have to
abide by the same limit, and it is unlikely that any existing client
even cares about using bitmap names this long.  It's time to codify
that ALL bitmaps managed by qemu (whether persistent in qcow2 or not)
have a documented maximum length.

Signed-off-by: Eric Blake <address@hidden>

Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

One doubt:

Is it good idea to include string larger than 4K into error message
(in next patch too)? I doubt that such message would be
readable, and I think that most possible source of such message is
some kind of memory corruption, so the whole message would be garbage,
which may contain special symbols which may look bad or even break

The string was provided by the user. You are correct that it results in a lot of output on stderr, but it is no more garbage than what the user provided in the first place. If we wanted, we could truncate (list only the first 256 or so bytes and then output "..."), but it's such a corner case error that I don't think it's worth the effort to worry about it.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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