Re: [PATCH v4 01/12] pkt-line: eliminate the need for static buffer in packet_write_gently()

On Fri, Feb 26, 2021 at 02:52:22PM -0500, Jeff Hostetler wrote:

quoted

quoted

-	if (fd >= 0)
-		err = write_packetized_from_fd(fd, process->in);
-	else
+	if (fd >= 0) {
+		struct packet_scratch_space scratch;
+		err = write_packetized_from_fd(fd, process->in, &scratch);
+	} else
  		err = write_packetized_from_buf(src, len, process->in);

Isn't this just putting the buffer onto the stack anyway? Your
scratch_space struct is really just a big array. You'd want to make
it static here, but then we haven't really solved anything. :)

Yeah, I was letting the caller decide how to provide the buffer.
They could put it on the stack or allocate it once across a whole
set of files or use a static buffer -- the caller has context for
what works best that we don't have here.  For example, the caller
may know that is not in threaded code at all, but we cannot assume
that here.

Yeah, I think it's successfully pushed the problem up to the caller. But
it introduced a _new_ problem in putting the large buffer on the stack.
So if this were "static struct packet_scratch_space scratch", I think
we'd be OK.

And perhaps that would meet your needs (if you just need to call
write_packed_from_fd() in a thread, and not this other caller).

But I do think the heap approach is nice in that it keeps the interface
clean, and I think the performance should be comparable.

Right, I think it would be fine to malloc it here, but I didn't
want to assume that everyone would think that.

I'll change it.

Thanks. :)

-Peff