[libvirt] [PATCH] nwfilter: save error from DHCP snoop thread to report in main thread

[Michal Privoznik]

On 02/23/2018 04:05 PM, Laine Stump wrote:
> A problem encountered due to a bug in libpcap was reported to the caller as:
> 
>    An error occurred, but the cause is unknown
> 
> This was because the error had been logged in the DHCPSnoop
> thread. The worker thread handling the API call to start a domain
> spins up the DHCPSnoop thread which watches for dhcp packets with
> libpcap, then uses virCondSignal() to notify the worker thread (which
> has been waiting with virCondWait()). The worker thread knows that
> there was an error (because threadStatus != THREAD_STATUS_OK), but the
> error info had been stored in thread-specific storage for the other
> thread, so the worker thread can only report that there was a failure,
> but it doesn't know why.
> 
> The solution is to save the error that was logged (with
> virErrorPreserveLast() into the object the is used to share info
> between the threads, then we can set the error in the worker thread
> using virErrorRestore().
> 
> In the case of the error I was looking at, this changed the "unknown"
> message into:
> 
>     internal error: pcap_setfilter: can't remove kernel filter:
>     Bad file descriptor
> 
> Signed-off-by: Laine Stump <laine at laine.org>
> ---
>  src/nwfilter/nwfilter_dhcpsnoop.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)

ACK and safe for freeze.

Michal