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[34.150.157.240]) by smtp.gmail.com with ESMTPSA id c18-20020a05620a269200b007343fceee5fsm136266qkp.8.2023.03.16.12.00.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Mar 2023 12:00:47 -0700 (PDT) Date: Thu, 16 Mar 2023 15:00:46 -0400 From: Willem de Bruijn To: David Howells , 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 Message-ID: <6413675eedcfa_33bc9d208e9@willemb.c.googlers.com.notmuch> In-Reply-To: <811534.1678992280@warthog.procyon.org.uk> References: <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> Subject: Re: [RFC PATCH 03/28] tcp: Support MSG_SPLICE_PAGES Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 0E46E80014 X-Rspamd-Server: rspam01 X-Stat-Signature: h7r7ikosj1dejne4zhrfhx5he49gpqoo X-HE-Tag: 1678993250-82333 X-HE-Meta: U2FsdGVkX19B6yOyxnM0DG+I1prKj5girPvoHxYUXOVtBuZlda/ah9/LyrtIwdNlW6xBbZzfXpIvHbMXjWuB9Tw8Ov0uuwHETKXwl0WocG5r1qcb5n33p7s3skwcUi4S3Lgpy6r7pCv+kti7ucyJB1Hpx9vO5NYec0UWucCfSi5C6LPYyBC9VKzIZu+dWN43yqOBAbsHSeSYicjGE9XLZVx9wEVdRoks7mMCCh5Q3Hx33gwK1mI2bYkftAs4hH3iEito7dfRk2CRcAJozY51ZTSbieu/GB3ljae7h9f7Cw+isf7UBmV3BMGsvw6wqwWBr1nl3peAYqKsbagLG4kkk+zpFMZP23q/YxUl8ZfN0+un/jir+ft9HdJlI++toXBweyN6+6fys5jqeICHr+5qN2X20DVXZLTxVoFXTqt5dYkHvgiGS9Aq7Blp7CyODWEJFPproYLTyi1h71kvz37j1d4HQ1swgcCNYUl/Qt7Z4c2LuLaWz3Oq3D6Qemic9Cy9fN+qj3R43BQBakSIxLqEw9GHkhzKpQi35dmD5v9cH1Ed0jT66e/48dUr/JZ5RbRS/H5RnPF7n0A0yDcmFXOtoWQVm2fFZpO66pCfrZ3tiMv4DEWGIzMjBoh7N4nLIfTwsQty6LIiTSG/Bv8H9Ppn/CmE7vO7KHj2Lye6WWtCTI3cXbkVVXi8qOJndZwx7wCl1hXyEEriMCFo3WyFO2q+MNWnpuC89X+WD51mlXV+U1CfAMzbWAAn5pGcvGK+03F5lVNMbsyD6HApC2/BhUHZAnu/5gxrhv7bySRszXIdOIUWWlI98DQamW1qf63+XDXPO+QNfcygRf3cKijzUvUx3FCy6lsKjqyfcknR/xMXdlz1hLvO9SZ9/Xubk7Fs8ozIH04Q4fcBeQuJU4eJNvwXMdSzf+FVvK9GwT+629BEG9uOLHOi2V9zn0T/BEAhAYFDz7afbLpXyAn1+1fCaAL dqUwPaS+ IzHkQKc4dOWrM/E89xU7Tkdw9PhtyzyKnmYEQTdDD+W9VhhkMUpgDoazLBcpEM7ONQht+K/FA/IzqSKD/3O7ucODj0RM1oISDY4szffAewcXZDGPLbcQJnh7yzEy6Qcm8kr2/Wc2Vaw8Z7zP1TbDsFAJ6Iy4ypyhoCgMP11peEyY9bz+1vAoH77sZmGnKxB3YOjw0o+xCwbUvye0NvOALycFvbovWczsj+B80+Z5NYkgh+GppsADxAePHGpKOOmr1MD4ogcpSQFet7ewtaeiP75JwyaFI9Y4ZkWTXaJXzGdi2zh8d8YMKY6cswJU1G7nbgRZtsmtkokBv9vRCSGTdcj1jyijGGtnjIKJeVDiU9uy0gok16nV5dl6/85UWwD/5rbvn9f/2eIUyWkf2kiRNlDV6BTZar+zyWn0fcfNkJCQ6Sf+ENqzZDtqstUFe4zb4jnyvDnTyUXk66mAqi+XPxykyQjTNEgoYF2nCfyihwwrd6EmuV+QCupj0rrBuRpeaFDCb99pTzWRaiCW0e7IVr6Zm3HRLxgQWllDICmx0RCLEZTQDTwcVvFEUDLS7zzuntWLMuJOPJdsenXeer720FWyGkfyWf9bTSbULnvDX/+uiSxY= 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: 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 checks > > 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 space as > the uapi flags. That would work, if no cost to common paths that don't need it. 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.