Re: [libvirt] [PATCH 05/27] Introduce virStreamRegisterSkip and virStreamSkipCallback
On 05.05.2016 16:49, Eric Blake wrote:
On 04/28/2016 04:04 AM, Michal Privoznik wrote:
> The former is a public API and registers a callback that
> will be called whenever the other side of a stream calls
> virStreamSkip. The latter is a wrapper that actually calls
> the callback. It is not made public as it is intended to be
> used purely internally.
>
> Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com>
> ---
> +/**
> + * virStreamSkipFunc:
> + * @stream: stream
> + * @offset: size of hole in bytes
Again, naming this 'length' makes more sense (you're not skipping TO a
particular offset, but OVER a given length).
> +++ b/src/libvirt-stream.c
> @@ -286,6 +286,76 @@ virStreamRecv(virStreamPtr stream,
>
>
> /**
> + * virStreamRegisterSkip:
> + * @stream: stream
> + * @skipCb: callback function
> + * @opaque: optional application provided data
> + *
> + * This function registers callback that will be called whenever
s/callback/a callback/
> + * the other side of the @stream is willing to skip a hole in the
> + * stream.
> + *
> + * Returns 0 on success,
> + * -1 otherwise.
> + */
> +int
> +virStreamRegisterSkip(virStreamPtr stream,
> + virStreamSkipFunc skipCb,
> + void *opaque)
> +{
> + VIR_DEBUG("stream=%p, skipCb=%p opaque=%p", stream, skipCb, opaque);
> +
> + virResetLastError();
> +
> + virCheckStreamReturn(stream, -1);
> + virCheckNonNullArgReturn(skipCb, -1);
> +
> + if (stream->skipCb) {
> + virReportError(VIR_ERR_OPERATION_INVALID, "%s",
> + _("A skip callback is already registered"));
> + return -1;
I guess that means we allow passing skipCb=NULL to deregister a
callback; does it need to be specifically documented? Are there
scenarios where you WANT to deregister before closing something else, to
make sure that a stale callback is not called during a race scenario?
I haven't thought of that. I mean, the line just above this check
prohibits skipCB being NULL. But it seems like this will be thrown away
anyway.
> +int
> +virStreamSkipCallback(virStreamPtr stream,
> + unsigned long long offset)
> +{
> + VIR_DEBUG("stream=%p, offset=%llu", stream, offset);
> +
> + virCheckStreamReturn(stream, -1);
> +
> + if (stream->skipCb) {
> + int ret;
> + ret = (stream->skipCb)(stream, offset, stream->skipCbOpaque);
I might have omitted the () around stream->skipCb, but I don't know if
we have a consistent style, and yours makes it obvious that we know we
are dereferencing a function pointer.
> +++ b/src/libvirt_public.syms
> @@ -735,6 +735,7 @@ LIBVIRT_1.3.3 {
> LIBVIRT_1.3.5 {
> global:
> virStreamSkip;
> + virStreamRegisterSkip;
Worth keeping sorted?
Sure.
Michal