[libvirt] [PATCH] Fix up connection reference counting.

[Daniel P. Berrange]

On Thu, Aug 13, 2009 at 10:51:46AM +0200, Chris Lalancette wrote:
> Currently the reference counting for connections is busted.  I
> first noticed it while trying to use virConnectRef; it would
> eventually cause a crash in the remote_internal driver, although
> that was really just a victim.  Really, we should only call the
> close callbacks on the methods when the references drop to 0.  To
> accomplish this, move all of the close callbacks into
> virUnrefConnect (since there are lots of internal users of that
> function), and arrange for virConnectClose to call that.
> 
> Signed-off-by: Chris Lalancette <clalance at redhat.com>
> ---
>  src/datatypes.c |   10 ++++++++++
>  src/libvirt.c   |   14 +-------------
>  2 files changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/src/datatypes.c b/src/datatypes.c
> index 9d556c8..83260c1 100644
> --- a/src/datatypes.c
> +++ b/src/datatypes.c
> @@ -237,6 +237,16 @@ virUnrefConnect(virConnectPtr conn)
>      conn->refs--;
>      refs = conn->refs;
>      if (refs == 0) {
> +        if (conn->networkDriver)
> +            conn->networkDriver->close (conn);
> +        if (conn->interfaceDriver)
> +            conn->interfaceDriver->close (conn);
> +        if (conn->storageDriver)
> +            conn->storageDriver->close (conn);
> +        if (conn->deviceMonitor)
> +            conn->deviceMonitor->close (conn);
> +        conn->driver->close (conn);
> +
>          virReleaseConnect(conn);
>          /* Already unlocked mutex */
>          return (0);

There's a minor annoying problem there in that you will deadlock
if any of those driver functions try to raise an error, since
you are holding the connection lock. So after if(ref ==0) you
need to release the lock, and then re-aquire it before calling
the virReleaseConnect().

> diff --git a/src/libvirt.c b/src/libvirt.c
> index 5aa7f83..472c19b 100644
> --- a/src/libvirt.c
> +++ b/src/libvirt.c
> @@ -1231,19 +1231,7 @@ virConnectClose(virConnectPtr conn)
>          return (-1);
>      }
>  
> -    if (conn->networkDriver)
> -        conn->networkDriver->close (conn);
> -    if (conn->interfaceDriver)
> -        conn->interfaceDriver->close (conn);
> -    if (conn->storageDriver)
> -        conn->storageDriver->close (conn);
> -    if (conn->deviceMonitor)
> -        conn->deviceMonitor->close (conn);
> -    conn->driver->close (conn);
> -
> -    if (virUnrefConnect(conn) < 0)
> -        return (-1);
> -    return (0);
> +    return virUnrefConnect(conn);
>  }
>  
>  /**


Daniel
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