Re: [Qemu-devel] [PATCH 8/10] Introduce a buffered QEMUFile wrapper

["Blue Swirl" <blauwirbel@gmail.com>]

On 9/9/08, Anthony Liguori <aliguori@us.ibm.com> wrote:
> This patch introduces a buffered QEMUFile wrapper.  This allows QEMUFile's to be
>  rate limited.  It also allows makes it easier to implement a QEMUFile that is
>  asynchronous.
>
>  The only real non-obvious part of the API is the "frozen" concept.  If the backend
>  returns EAGAIN, the QEMUFile is said to be "frozen".  This means no additional
>  output will be sent to the backend until the file is unfrozen.  qemu_file_put_notify
>  can be used to unfreeze a frozen file.
>
>  A synchronous interface is also provided to wait for an unfreeze event.  This is
>  used during the final part of live migration when the VM is no longer running.

>  +static int buffered_put_buffer(void *opaque, const uint8_t *buf, int64_t pos, int size)
>  +{
>  +    QEMUFileBuffered *s = opaque;
>  +    size_t offset = 0;
>  +    ssize_t ret;
>  +
>  +    if (s->has_error)
>  +        return -EINVAL;
>  +
>  +    s->freeze_output = 0;
>  +
>  +    buffered_flush(s);
>  +
>  +    while (offset < size) {
>  +        if (s->bytes_xfer > s->xfer_limit)
>  +            break;
>  +
>  +        ret = s->put_buffer(s->opaque, buf + offset, size - offset);
>  +        if (ret == -EAGAIN) {
>  +            s->freeze_output = 1;
>  +            break;
>  +        }
>  +
>  +        if (ret <= 0) {
>  +            s->has_error = 1;
>  +            break;
>  +        }
>  +
>  +        offset += ret;
>  +        s->bytes_xfer += ret;
>  +    }
>  +
>  +    buffered_append(s, buf + offset, size - offset);
>  +
>  +    return offset;
>  +}

I'd change the types of the return value and parameter "size" to ssize_t.