Re: [Xen-devel] [PATCH] tools/libxenforeignmemory: add a call to restrict the handle

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 27/03/2017 09:06, Paul Durrant wrote:
>> -----Original Message-----
>> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of
>> Paul Durrant
>> Sent: 24 March 2017 20:24
>> To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>; xen-
>> devel@xxxxxxxxxxxxxxxxxxxx
>> Cc: Ian Jackson <Ian.Jackson@xxxxxxxxxx>; Julien Grall
>> <julien.grall@xxxxxxx>; Wei Liu <wei.liu2@xxxxxxxxxx>
>> Subject: Re: [Xen-devel] [PATCH] tools/libxenforeignmemory: add a call to
>> restrict the handle
>>
>>> -----Original Message-----
>>> From: Andrew Cooper
>>> Sent: 24 March 2017 20:10
>>> To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>; xen-
>> devel@xxxxxxxxxxxxxxxxxxxx
>>> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>; Ian Jackson <Ian.Jackson@xxxxxxxxxx>;
>>> Julien Grall <julien.grall@xxxxxxx>
>>> Subject: Re: [Xen-devel] [PATCH] tools/libxenforeignmemory: add a call to
>>> restrict the handle
>>>
>>> On 22/03/17 11:25, Paul Durrant wrote:
>>>> diff --git a/tools/libs/foreignmemory/libxenforeignmemory.map
>>> b/tools/libs/foreignmemory/libxenforeignmemory.map
>>>> index df206b3..5c9806c 100644
>>>> --- a/tools/libs/foreignmemory/libxenforeignmemory.map
>>>> +++ b/tools/libs/foreignmemory/libxenforeignmemory.map
>>>> @@ -4,5 +4,6 @@ VERS_1.0 {
>>>>            xenforeignmemory_close;
>>>>            xenforeignmemory_map;
>>>>            xenforeignmemory_unmap;
>>>> +          xenforeignmemory_restrict;
>>>>    local: *; /* Do not expose anything by default */
>>>>  };
>>> This isn't correct.
>>>
>>> New functions like this need to bump at least the SO minor version, like
>>> c/s f1446de4ba
>>>
>> Sorry, yes, I forgot these libraries are supposed to be stable now.
>>
>>> Fixing this is a blocker to releasing 4.9
>>>
>> I'll submit a patch on Monday.
> Actually, on second thoughts, do we want to bump the version for all changes 
> or just incompatible ones? I added a call here so it shouldn't break any 
> older application compiling against this library.

You must bump the versions; the version information gets embedded as
part of the dynamic linkage of the application built against
libxenforeignmemory.

In particular, you need to prevent an application built now from
referencing xenforeignmemory_restrict@1.0 because the version 1.0
shipped in all earlier versions of Xen lacked this function.

Not bumping the version now will result in newer applications being
built which the dynamic loader thinks will work with older versions of
the library, rather than correctly identifying that a newer version of
the library is required.

As with other things in staging, it can get away with only being bumped
once per Xen release, but it must always be bumped at the first change.

~Andrew

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