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b534dc46c8
Add an option to initialize SOF_TIMESTAMPING_OPT_ID for TCP from write_seq sockets instead of snd_una. This should have been the behavior from the start. Because processes may now exist that rely on the established behavior, do not change behavior of the existing option, but add the right behavior with a new flag. It is encouraged to always set SOF_TIMESTAMPING_OPT_ID_TCP on stream sockets along with the existing SOF_TIMESTAMPING_OPT_ID. Intuitively the contract is that the counter is zero after the setsockopt, so that the next write N results in a notification for the last byte N - 1. On idle sockets snd_una == write_seq and this holds for both. But on sockets with data in transmission, snd_una records the unacked offset in the stream. This depends on the ACK response from the peer. A process cannot learn this in a race free manner (ioctl SIOCOUTQ is one racy approach). write_seq records the offset at the last byte written by the process. This is a better starting point. It matches the intuitive contract in all circumstances, unaffected by external behavior. The new timestamp flag necessitates increasing sk_tsflags to 32 bits. Move the field in struct sock to avoid growing the socket (for some common CONFIG variants). The UAPI interface so_timestamping.flags is already int, so 32 bits wide. Reported-by: Sotirios Delimanolis <sotodel@meta.com> Signed-off-by: Willem de Bruijn <willemb@google.com> Link: https://lore.kernel.org/r/20221207143701.29861-1-willemdebruijn.kernel@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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