Re: [Qemu-devel] [PATCH v1 4/7] io: pass a struct iovec into qio_channel_websock_encode

[Eric Blake]

On 10/10/2017 10:43 AM, Daniel P. Berrange wrote:
> Instead of requiring use of another Buffer, pass a struct iovec
> into qio_channel_websock_encode, which gives callers more
> flexibility in how they process data.
> 
> Signed-off-by: Daniel P. Berrange <address@hidden>
> ---
>  io/channel-websock.c | 69 
> ++++++++++++++++++++++++++++++++--------------------
>  1 file changed, 42 insertions(+), 27 deletions(-)
> 

> +static void qio_channel_websock_encode(QIOChannelWebsock *ioc,
> +                                       uint8_t opcode,
> +                                       const struct iovec *iov,
> +                                       size_t niov,
> +                                       size_t size)
>  {

Is size redundant with iov_size(iov, niov)?  Or is a caller allowed to
pass a smaller size (tail end of iov is not encoded) or larger size
(encoding stops at end of iov, even if size is not exhausted)?  I'd lean
towards the former (one less parameter), especially since all callers in
this patch could have passed iov_size(&iov, 1) for the same effect.

> -    trace_qio_channel_websock_encode(ioc, opcode, header_size, 
> buffer->offset);
> -    buffer_reserve(output, header_size + buffer->offset);
> -    buffer_append(output, header.buf, header_size);
> -    buffer_append(output, buffer->buffer, buffer->offset);
> +    trace_qio_channel_websock_encode(ioc, opcode, header_size, size);
> +    buffer_reserve(&ioc->encoutput, header_size + size);
> +    buffer_append(&ioc->encoutput, header.buf, header_size);
> +    for (i = 0; i < niov && size != 0; i++) {
> +        size_t want = iov->iov_len;
> +        if (want > size) {
> +            want = size;
> +        }
> +        buffer_append(&ioc->encoutput, iov->iov_base, want);
> +        size -= want;
> +    }

Umm, where are you incrementing iov? It appears you only tested with
niov == 1.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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