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Re: [libvirt] [PATCH 1/5 v2] Add public API to register a callback to be invoked on connection close



On 07/20/2012 08:21 AM, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange redhat com>
> 
> Define a new virConnectSetCloseCallback() public API which allows
> registering a callback to be invoked when the connection to a
> hypervisor is closed. The callback is provided with the reason for
> the close, which may be 'error', 'eof' or 'keepalive'.
> 
> Signed-off-by: Daniel P. Berrange <berrange redhat com>
> ---
>  include/libvirt/libvirt.h.in |   40 +++++++++++++++++++++-------
>  src/datatypes.c              |    4 +++
>  src/datatypes.h              |    5 ++++
>  src/libvirt.c                |   60 ++++++++++++++++++++++++++++++++++++++++++
>  src/libvirt_public.syms      |    6 +++++
>  5 files changed, 105 insertions(+), 10 deletions(-)
> 
> diff --git a/include/libvirt/libvirt.h.in b/include/libvirt/libvirt.h.in
> index e34438c..85d8c8a 100644
> --- a/include/libvirt/libvirt.h.in
> +++ b/include/libvirt/libvirt.h.in
> @@ -49,6 +49,17 @@ extern "C" {
>   * defines VIR_ENUM_SENTINELS.  Enumerations for bit values do not
>   * have a *_LAST value, but additional bits may be defined.  */
>  
> +/*
> + * virFreeCallback:
> + * @opaque: opaque user data provided at registration
> + *
> + * Type for a domain event callback when the event is deregistered and
> + * need to be freed, @opaque is provided along with the callback at
> + * registration time
> + */
> +typedef void (*virFreeCallback)(void *opaque);

We're now using this for more than just domain events; the comment needs
a slight update.  Maybe:

Type for a callback cleanup function to be paired with a callback.  This
function will be called as a final chance to clean up the @opaque
registered with the primary callback, at the time when the primary
callback is deregistered.

> +++ b/src/datatypes.c
> @@ -115,6 +115,10 @@ virReleaseConnect(virConnectPtr conn) {
>  
>      virMutexLock(&conn->lock);
>  
> +    if (conn->closeOpaque &&
> +        conn->closeFreeCallback)
> +        conn->closeFreeCallback(conn->closeOpaque);

I'm still not sure I like filtering on NULL opaque.  Our other uses of a
virFreeCallback include src/fdstream.c:virFDStreamRemoveCallback, and
there we call fdst->ff without regards to whether fdst->opaque is null.

> +int virConnectSetCloseCallback(virConnectPtr conn,
> +                               virConnectCloseFunc cb,
> +                               void *opaque,
> +                               virFreeCallback freecb)
> +{
> +    VIR_DEBUG("conn=%p", conn);
> +
> +    virResetLastError();
> +
> +    if (!VIR_IS_CONNECT(conn)) {
> +        virLibConnError(VIR_ERR_INVALID_CONN, __FUNCTION__);
> +        virDispatchError(NULL);
> +        return -1;
> +    }
> +
> +    virMutexLock(&conn->lock);
> +
> +    if (conn->closeCallback) {
> +        virLibConnError(VIR_ERR_OPERATION_INVALID, "%s",
> +                        _("A close callback is already registered"));
> +        goto error;
> +    }

Do we want to allow deregistration of a close callback (we have
virConnectDomainEventDeregister, after all).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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