Re: [PATCH RFC v2 00/12] socket sendmsg MSG_ZEROCOPY

On Tue, 2017-02-28 at 22:28 -0500, David Miller wrote:

These device are already choking, because as I stated this can already
be done via sendfile().

Networking card wise this isn't an issue, chips bring the entire packet
into their FIFO, compute checksums on the fly mid-stream, and then write
the 16-bit checksum field before starting to write the packet onto the
wire.

I think this is completely a non-issue, and we thought about this right
from the start when sendfile() support was added nearly two decades ago.
If network cards from back then didn't crap out in this situation I
think the ones out there now are probably ok.

Well, we had to fix one issue with GSO fall back about 4 years ago.

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=cef401de7be8c4e155c6746bfccf721a4fa5fab9

So extra scrutiny would be nice.

Zero copy is incredibly hard to get right.