On Sun, Mar 25, 2018 at 01:55:07AM +0530, Sukrit Bhatnagar wrote:
> Hi,
>
> I am interested in implementing the GCC cleanup attribute for automatic
> resource freeing as part of GSoC'18. I have shared a proposal for the same.
>
> This mail is to discuss the code design for implementing it.
>
>
> Here are some of my ideas:
>
> This attribute requires a cleanup function that is called automatically
> when the corresponding variable goes out of scope. There are some functions
> whose logic can be reused:
>
> - Functions such as virCommandFree, virConfFreeList and virCgroupFree can
> be directly used as cleanup functions. They have parameter and return type
> valid for a cleanup function.
>
> - Functions such as virFileClose and virFileFclose need some additional
> consideration as they return a value. I think we can set some global
> variable in a separate source file (just like errno variable from errno.h).
> Then the value to be returned can be accessed globally.
Note we call VIR_FORCE_CLOSE and VIR_FORCE_FCLOSE in cleanup scenarios
to explicitly ignore the return value. We only care about checking
return value for VIR_CLOSE and VIR_FCLOSE in a tiny set of cases.
>
> - Functions such as virDomainEventGraphicsDispose need an entirely new
> design. They are used as callbacks in object classes and passed as an
> argument in virClassNew. This would require making changes to
> virObjectUnref's code too. *This is the part I am not sure how to implement
> cleanup logic for.*
There shouldn't be any need to touch the DIspose funtions - that's internal
helper code. To "free" an object variable, you just want to end up invoking
the regular virObjectUnref function as the cleanup func.
> Also, since the __attribute__((__cleanup__(anyfunc))) looks ugly, a macro
> like autoclean (ideas for macro name welcome!) can be used instead. As
> Martin pointed out in my proposal, for some types, this can be done right
> after typedef declarations, so that the type itself contains this attribute.
Just suffix it with "Auto", eg virDomainAutoPtr, vs virDomainPtr.
> I can create new files vircleanup.{c,h} for defining cleanup functions for
> types which do not have an existing cleanup/free function. This can be done
> separately for each driver supported.
> For example, cleanups pertaining to lxc driver will be in
> src/lxc/lxc_cleanup.c.
I'm not rally seeing a compelling need for this - just add it in appropriate
existing files.
Regards,
Daniel
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