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Re: [PATCH v3 1/6] xen: add reference counter support
- To: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Wed, 12 Apr 2023 12:12:06 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Wed, 12 Apr 2023 10:12:34 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Tue, Apr 11, 2023 at 10:27:45PM +0000, Volodymyr Babchuk wrote:
>
> Hello Roger,
>
> Sorry for the late answer.
>
> Roger Pau Monné <roger.pau@xxxxxxxxxx> writes:
>
> > On Tue, Mar 14, 2023 at 08:56:29PM +0000, Volodymyr Babchuk wrote:
> >> We can use reference counter to ease up object lifetime management.
> >> This patch adds very basic support for reference counters. refcnt
> >> should be used in the following way:
> >>
> >> 1. Protected structure should have refcnt_t field
> >>
> >> 2. This field should be initialized with refcnt_init() during object
> >> construction.
> >>
> >> 3. If code holds a valid pointer to a structure/object it can increase
> >> refcount with refcnt_get(). No additional locking is required.
> >>
> >> 4. Code should call refcnt_put() before dropping pointer to a
> >> protected structure. `destructor` is a call back function that should
> >> destruct object and free all resources, including structure protected
> >> itself. Destructor will be called if reference counter reaches zero.
> >>
> >> 5. If code does not hold a valid pointer to a protected structure it
> >> should use other locking mechanism to obtain a pointer. For example,
> >> it should lock a list that hold protected objects.
> >
> > Sorry, I didn't look at the previous versions, but did we consider
> > importing refcount_t and related logic from Linux?
>
> Well, I considered this. But it is more complex. It has separate
> refcount module, which just counts references + kref code, that is
> capable of calling destructors. I am not sure if Xen need this
> division. In any case, I tried to replicate Linux behavior as close as
> possible. On other hand, Jan suggests to rework API, so it will be
> differ from Linux one...
OK, just asking because it's likely for the interface to grow if there
are more users of refcounting, and at some point we might need a set
of features similar to Linux.
Thanks, Roger.
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