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[73.158.218.242]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-231d4afe856sm21022455ad.86.2025.05.16.19.17.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 May 2025 19:17:23 -0700 (PDT) Date: Fri, 16 May 2025 19:17:23 -0700 From: Stanislav Fomichev To: Al Viro Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, willemb@google.com, sagi@grimberg.me, asml.silence@gmail.com, almasrymina@google.com, kaiyuanz@google.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next] net: devmem: remove min_t(iter_iov_len) in sendmsg Message-ID: References: <20250517000431.558180-1-stfomichev@gmail.com> <20250517000907.GW2023217@ZenIV> <20250517020653.GX2023217@ZenIV> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20250517020653.GX2023217@ZenIV> On 05/17, Al Viro wrote: > On Fri, May 16, 2025 at 06:24:03PM -0700, Stanislav Fomichev wrote: > > On 05/17, Al Viro wrote: > > > On Fri, May 16, 2025 at 05:04:31PM -0700, Stanislav Fomichev wrote: > > > > iter_iov_len looks broken for UBUF. When iov_iter_advance is called > > > > for UBUF, it increments iov_offset and also decrements the count. > > > > This makes the iterator only go over half of the range (unless I'm > > > > missing something). > > > > > > What do you mean by "broken"? iov_iter_len(from) == "how much data is > > > left in that iterator". That goes for all flavours, UBUF included... > > > > > > Confused... > > [snip] > > > iov_len. And now, calling iter_iov_len (which does iov_len - iov_offset) > > Wait a sec... Sorry, I've misread that as iov_iter_count(); iter_iov_len() > (as well as iter_iov_addr()) should not be used on anything other that > ITER_IOVEC > > > > Wait, in the same commit there's > + if (iov_iter_type(from) != ITER_IOVEC) > + return -EFAULT; > > shortly prior to the loop iter_iov_{addr,len}() are used. What am I missing now? Yeah, I want to remove that part as well: https://lore.kernel.org/netdev/20250516225441.527020-1-stfomichev@gmail.com/T/#u Otherwise, sendmsg() with a single IOV is not accepted, which makes not sense.