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Re: [libvirt] [PATCH v3 07/31] Introduce VIR_STREAM_RECV_STOP_AT_HOLE flag




On 05/16/2017 10:03 AM, Michal Privoznik wrote:
> Add a new flag to virStreamRecvFlags in order to handle being able to
> stop reading from the stream so that the consumer can generate a "hole"
> in stream target. Generation of a hole replaces the need to receive and
> handle a sequence of zero bytes for sparse stream targets.
> 
> Signed-off-by: Michal Privoznik <mprivozn redhat com>
> ---
>  include/libvirt/libvirt-stream.h |  4 ++++
>  src/libvirt-stream.c             | 34 +++++++++++++++++++++++++++++++++-
>  2 files changed, 37 insertions(+), 1 deletion(-)
> 
> diff --git a/include/libvirt/libvirt-stream.h b/include/libvirt/libvirt-stream.h
> index feaa8ad64..c4baaf7a3 100644
> --- a/include/libvirt/libvirt-stream.h
> +++ b/include/libvirt/libvirt-stream.h
> @@ -45,6 +45,10 @@ int virStreamRecv(virStreamPtr st,
>                    char *data,
>                    size_t nbytes);
>  
> +typedef enum {
> +    VIR_STREAM_RECV_STOP_AT_HOLE = (1 << 0),
> +} virStreamRecvFlagsValues;
> +
>  int virStreamRecvFlags(virStreamPtr st,
>                         char *data,
>                         size_t nbytes,
> diff --git a/src/libvirt-stream.c b/src/libvirt-stream.c
> index dc0dc9ea3..bedb6159a 100644
> --- a/src/libvirt-stream.c
> +++ b/src/libvirt-stream.c
> @@ -290,7 +290,7 @@ virStreamRecv(virStreamPtr stream,
>   * @stream: pointer to the stream object
>   * @data: buffer to read into from stream
>   * @nbytes: size of @data buffer
> - * @flags: extra flags; not used yet, so callers should always pass 0
> + * @flags: bitwise-OR of virStreamRecvFlagsValues
>   *
>   * Reads a series of bytes from the stream. This method may
>   * block the calling application for an arbitrary amount
> @@ -300,6 +300,33 @@ virStreamRecv(virStreamPtr stream,
>   * @flags. Calling this function with no @flags set (equal to
>   * zero) is equivalent to calling virStreamRecv(stream, data, nbytes).
>   *
> + * If flag VIR_STREAM_RECV_STOP_AT_HOLE is set, this function
> + * will stop reading from stream if it has reached a hole. In
> + * that case, -3 is returned and virStreamRecvHole() should be
> + * called to get the hole size. An example using this flag might
> + * look like this:
> + *
> + *   while (1) {
> + *     char buf[4096];
> + *
> + *     int ret = virStreamRecvFlags(st, buf, len, VIR_STREAM_STOP_AT_HOLE);
> + *     if (ret < 0) {
> + *       if (ret == -3) {
> + *         long long len;
> + *         ret = virStreamRecvHole(st, &len, 0);
> + *         if (ret < 0) {
> + *           ...error..
> + *         } else {
> + *           ...seek len bytes in target...

Do/should we care to point out that @len is a "long long" and seeking is
done in chunks of "off_t"?

Reviewed-by: John Ferlan <jferlan redhat com>

John

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