On 05/16/2017 10:03 AM, Michal Privoznik wrote:
> This API is used to tell the other side of the stream to skip
> some bytes in the stream. This can be used to create a sparse
> file on the receiving side of a stream.
>
> It takes @length argument, which says how big the hole is. This
> skipping is done from the current point of stream. Since our
> streams are not rewindable like regular files, we don't need
> @whence argument like seek(2) has.
>
> Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
> ---
> include/libvirt/libvirt-stream.h | 4 +++
> src/driver-stream.h | 6 ++++
> src/libvirt-stream.c | 61 ++++++++++++++++++++++++++++++++++++++++
> src/libvirt_public.syms | 1 +
> 4 files changed, 72 insertions(+)
>
[...]
> diff --git a/src/libvirt-stream.c b/src/libvirt-stream.c
> index 7535deb3c..a09896dcd 100644
> --- a/src/libvirt-stream.c
> +++ b/src/libvirt-stream.c
> @@ -344,6 +344,67 @@ virStreamRecvFlags(virStreamPtr stream,
> }
>
>
> +/**
> + * virStreamSendHole:
> + * @stream: pointer to the stream object
> + * @length: number of bytes to skip
> + * @flags: extra flags; not used yet, so callers should always pass 0
> + *
> + * Rather than transmitting empty file space, this API directs
> + * the @stream target to create @length bytes of empty space.
> + * This API would be used when uploading or downloading sparsely
> + * populated files to avoid the needless copy of empty file
> + * space.
> + *
> + * An example using this with a hypothetical file upload API
> + * looks like:
> + *
> + * virStream st;
> + *
> + * while (1) {
> + * char buf[4096];
> + * size_t len;
> + * if (..in hole...) {
> + * ..get hole size...
> + * virStreamSendHole(st, len, 0);
> + * } else {
> + * ...read len bytes...
> + * virStreamSend(st, buf, len);
> + * }
> + * }
> + *
> + * Returns 0 on success,
> + * -1 error
> + */
> +int
> +virStreamSendHole(virStreamPtr stream,
> + long long length,
> + unsigned int flags)
> +{
> + VIR_DEBUG("stream=%p, length=%lld flags=%x",
> + stream, length, flags);
> +
> + virResetLastError();
> +
> + virCheckStreamReturn(stream, -1);
Perhaps some preventative programming:
virCheckNonNegativeArgGoto(length, error);
Although that would mean calling virDispatchError unless there was some
sort of virCheck*ArgReturn(length, -1)
Reviewed-by: John Ferlan <jferlan@xxxxxxxxxx>
John
[...]
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