On Wed, Jun 23, 2021 at 02:58:32PM -0700, Omar Sandoval wrote:
> Ah, I was stuck on thinking about this calling convention:
>
> struct encoded_iov encoded_iov;
> char compressed_data[...];
> struct iovec iov[] = {
> { &encoded_iov, sizeof(encoded_iov) },
> { compressed_data, sizeof(compressed_data) },
> };
> preadv2(fd, iov, 2, -1, RWF_ENCODED);
>
> But what you described would look more like:
>
> // Needs to be large enough for maximum returned header + data.
> char buffer[...];
> struct iovec iov[] = {
> { buffer, sizeof(buffer) },
> };
> preadv2(fd, iov, 2, -1, RWF_ENCODED);
> // We should probably align the buffer.
> struct encoded_iov *encoded_iov = (void *)buffer;
> char *data = buffer + encoded_iov->size;
>
> That's a little uglier, but it should work, and allows for arbitrary
> extensions. So, among these three alternatives (fixed size structure
> with reserved space, variable size structure like above, or ioctl),
> which would you prefer?
Variable-sized structure would seem to be the easiest from the kernel
POV and the interface is the easiest to describe - "you read the
encoded data preceded by the header"...
