On 10/24/24 18:19, Jens Axboe wrote:
On 10/24/24 10:06 AM, Pavel Begunkov wrote:
On 10/24/24 16:45, Jens Axboe wrote:
...
bv = kmsg->bvec;
for_each_iov {
struct iovec iov;
unsafe_get_user(iov.iov_base, &user_iovec->iov_base, foo);
unsafe_get_user(iov.iov_len, &user_iovec->iov_len, foo);
import_to_bvec(bv, &iov);
user_iovec++;
bv++;
}
if it can be done at prep time, because then there's no need to store
the iovec at all, it's already stable, just in bvecs. And this avoids
overlapping iovec/bvec memory, and it avoids doing two iterations for
import. Purely a poc, just tossing out ideas.
But I haven't looked too closely at your series yet. In any case,
whatever ends up working for you, will most likely be find for the
bundled zerocopy send (non-vectored) as well, and I can just put it on
top of that.
And you just made one towards delaying the imu resolution, which
is conceptually the right thing to do because of the mess with
links, just like it is with fixed files. That's why it need to
copy the iovec at the prep stage and resolve at the issue time.
Indeed, prep time is certainly the place to do it. And the above
incremental import should work fine then, as we won't care abot
user_iovec being stable being prep.
Seems like you're agreeing but then stating the opposite, there
is some confusion. I'm saying that IMHO the right API wise way
is resolving an imu at issue time, just like it's done for fixed
files, and what your recent series did for send zc.
Yeah early morning confusion I guess. And I do agree in principle,
though for registered buffers, those have to be registered upfront
anyway, so no confusion possible with prep vs issue there. For provided
buffers, it only matters for the legacy ones, which generally should not
be used. Doesn't change the fact that you're technically correct, the
right time to resolve them would be at issue time.
I'm talking about sendmsg with iovec. Registered buffers should
be registered upfront, that's right, but iovec should be copied
at prep, and finally resolved into bvecs incl the imu/buffer lookup
at the issue time. And those are two different points in time,
maybe because of links, draining or anything else. And if they
should be at different moments, there is no way to do it while
copying iovec.
--
Pavel Begunkov
