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Re: xenstore_lib.h and libxenstore API/ABI problems
- To: Jürgen Groß <jgross@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 2 Mar 2021 16:54:14 +0000
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- Cc: Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02/03/2021 15:33, Jürgen Groß wrote:
> On 02.03.21 16:23, Andrew Cooper wrote:
>> Hello,
>>
>> This is a total mess.
>>
>> libxenstored does not have a stable ABI. xenstore_lib.h contains:
>>
>> * struct xs_permissions, which contains an enum - one of the very common
>> ABI traps.
>>
>> * the prototypes for expanding_buffer_ensure(), sanitise_value() and
>> unsanitise_value(), which are inappropriately-namespaced symbols in
>> libxenstore
>>
>> * struct expanding_buffer with a classic string-handling trap (int len).
>>
>> * Various xenstored-internal details such as struct xs_tdb_record_hdr,
>> the internal permission bits, as well as stuff like
>> xs_daemon_{root,run}dir(), and worse xs_daemon_tdb(), which have
>> absolutely no business being external to xenstored.
>>
>>
>> Its clear that most of this shouldn't be part of libxenstore, but that
>> ship has sailed. 3.0.3 is broken and cannot be fixed.
>>
>> My best suggestion is that we freeze 3.0.3 where it is, and create a 4.0
>> which has all of the xenstore_lib.h content deleted. That, AFAICT, gets
>> us something which is 99% compatible, and stands a chance of being able
>> to kept properly stable.
>>
>> Thoughts?
>
> How would that work in practice?
>
> Would we ship both libraries, or only 4.0?
I *think* we can create 4.0 with just a tweak to the map file. Then, we
could build 3.0.3 side by side with 4.0.
We already have the compat for xenstore/xs{,lib}.h which adds to this
mess. I was thinking of adding a build time "want xenstore compat"
option which gets you 3.0.3 and the badly-named headers.
~Andrew
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