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Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <6413675eedcfa_33bc9d208e9@willemb.c.googlers.com.notmuch> References: <6413675eedcfa_33bc9d208e9@willemb.c.googlers.com.notmuch> <641361cd8d704_33b0cc20823@willemb.c.googlers.com.notmuch> <20230316152618.711970-1-dhowells@redhat.com> <20230316152618.711970-4-dhowells@redhat.com> <811534.1678992280@warthog.procyon.org.uk> To: Willem de Bruijn Cc: dhowells@redhat.com, Matthew Wilcox , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Al Viro , Christoph Hellwig , Jens Axboe , Jeff Layton , Christian Brauner , Linus Torvalds , netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH 03/28] tcp: Support MSG_SPLICE_PAGES MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <2040078.1679359126.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Tue, 21 Mar 2023 00:38:46 +0000 Message-ID: <2040079.1679359126@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 X-Stat-Signature: pqqhc3wsf8ksw7onm4koueggiixorrkq X-Rspam-User: X-Rspamd-Queue-Id: C1E3940013 X-Rspamd-Server: rspam06 X-HE-Tag: 1679359136-624216 X-HE-Meta: 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 FvGgQDUZ /DgnE13UjA5nfUJSAw20FQP+d2Ol3VL8oXMa08l8Q6Dq7urDTbkvwzqa5hPG22PTWldTNepqZTuAkEbgpZO2swUoMR90dZ3rTa9gHn1ExXoskU4adF7cyAuBTmIaxUUH/sTu2AZZfdSlnUUfcrPk0iN5iDXojLris4B+XAQPtSAgr5npHjA/BGXZVTv68KnhNBdBx0x867a45yqaTboIZfDzyN/krzgUgAkuyp5LOg1vm0z4yC9NE6lIO+SnaAzN9lxLqTmOcP4KCXl808RAVY8kkzNVakWMXYE3xTlrH0rPTg0/QWpcATqlzpKnqeHxzrgmm X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Willem de Bruijn wrote: > David Howells wrote: > > Willem de Bruijn wrote: > > = > > > The commit message mentions MSG_SPLICE_PAGES as an internal flag. > > > = > > > It can be passed from userspace. The code anticipates that and check= s > > > preconditions. > > = > > Should I add a separate field in the in-kernel msghdr struct for such = internal > > flags? That would also avoid putting an internal flag in the same spa= ce as > > the uapi flags. > = > That would work, if no cost to common paths that don't need it. Actually, it might be tricky. __ip_append_data() doesn't take a msghdr st= ruct pointer per se. The "void *from" argument *might* point to one - but it depends on seeing a MSG_SPLICE_PAGES or MSG_ZEROCOPY flag, otherwise we do= n't know. Possibly this changes if sendpage goes away. > A not very pretty alternative would be to add an an extra arg to each > sendmsg handler that is used only when called from sendpage. > = > There are a few other internal MSG_.. flags, such as > MSG_SENDPAGE_NOPOLICY. Those are all limited to sendpage, and ignored > in sendmsg, I think. Which would explain why it was clearly safe to > add them. Should those be moved across to the internal flags with MSG_SPLICE_PAGES? David