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([2620:10d:c092:600::1:9142]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ad52d04b08bsm1053154166b.13.2025.05.22.01.29.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 22 May 2025 01:29:47 -0700 (PDT) Message-ID: Date: Thu, 22 May 2025 09:31:04 +0100 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next 1/3] net: devmem: support single IOV with sendmsg To: Stanislav Fomichev , Mina Almasry Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, viro@zeniv.linux.org.uk, horms@kernel.org, andrew+netdev@lunn.ch, shuah@kernel.org, sagi@grimberg.me, willemb@google.com, jdamato@fastly.com, kaiyuanz@google.com, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20250520203044.2689904-1-stfomichev@gmail.com> Content-Language: en-US From: Pavel Begunkov In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/21/25 18:33, Stanislav Fomichev wrote: > On 05/21, Mina Almasry wrote: >> On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev wrote: >>> >>> sendmsg() with a single iov becomes ITER_UBUF, sendmsg() with multiple >>> iovs becomes ITER_IOVEC. iter_iov_len does not return correct >>> value for UBUF, so teach to treat UBUF differently. >>> >>> Cc: Al Viro >>> Cc: Pavel Begunkov >>> Cc: Mina Almasry >>> Fixes: bd61848900bf ("net: devmem: Implement TX path") >>> Signed-off-by: Stanislav Fomichev >>> --- >>> include/linux/uio.h | 8 +++++++- >>> net/core/datagram.c | 3 ++- >>> 2 files changed, 9 insertions(+), 2 deletions(-) >>> >>> diff --git a/include/linux/uio.h b/include/linux/uio.h >>> index 49ece9e1888f..393d0622cc28 100644 >>> --- a/include/linux/uio.h >>> +++ b/include/linux/uio.h >>> @@ -99,7 +99,13 @@ static inline const struct iovec *iter_iov(const struct iov_iter *iter) >>> } >>> >>> #define iter_iov_addr(iter) (iter_iov(iter)->iov_base + (iter)->iov_offset) >>> -#define iter_iov_len(iter) (iter_iov(iter)->iov_len - (iter)->iov_offset) >>> + >>> +static inline size_t iter_iov_len(const struct iov_iter *i) >>> +{ >>> + if (i->iter_type == ITER_UBUF) >>> + return i->count; >>> + return iter_iov(i)->iov_len - i->iov_offset; >>> +} >>> >> >> This change looks good to me from devmem perspective, but aren't you >> potentially breaking all these existing callers to iter_iov_len? >> >> ackc -i iter_iov_len >> fs/read_write.c >> 846: iter_iov_len(iter), ppos); >> 849: iter_iov_len(iter), ppos); >> 858: if (nr != iter_iov_len(iter)) >> >> mm/madvise.c >> 1808: size_t len_in = iter_iov_len(iter); >> 1838: iov_iter_advance(iter, iter_iov_len(iter)); >> >> io_uring/rw.c >> 710: len = iter_iov_len(iter); >> >> Or are you confident this change is compatible with these callers for >> some reason? > > Pavel did go over all callers, see: > https://lore.kernel.org/netdev/7f06216e-1e66-433e-a247-2445dac22498@gmail.com/ Yes, the patch should work Reviewed-by: Pavel Begunkov > >> Maybe better to handle this locally in zerocopy_fill_skb_from_devmem, >> and then follow up with a more ambitious change that streamlines how >> all the iters behave. > > Yes, I can definitely do that, but it seems a bit strange that the > callers need to distinguish between IOVEC and UBUF (which is a 1-entry > IOVEC), so having working iter_iov_len seems a bit cleaner. It might be a good idea to rename it at some point to highlight that it also works with ubufs (but not as a part of this fix). -- Pavel Begunkov