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    Subject[RFC PATCH v2 04/48] net: Declare MSG_SPLICE_PAGES internal sendmsg() flag
    Date
    Declare MSG_SPLICE_PAGES, an internal sendmsg() flag, that hints to a
    network protocol that it should splice pages from the source iterator
    rather than copying the data if it can. This flag is added to a list that
    is cleared by sendmsg and recvmsg syscalls on entry.

    This is intended as a replacement for the ->sendpage() op, allowing a way
    to splice in several multipage folios in one go.

    Signed-off-by: David Howells <dhowells@redhat.com>
    cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
    cc: "David S. Miller" <davem@davemloft.net>
    cc: Eric Dumazet <edumazet@google.com>
    cc: Jakub Kicinski <kuba@kernel.org>
    cc: Paolo Abeni <pabeni@redhat.com>
    cc: Jens Axboe <axboe@kernel.dk>
    cc: Matthew Wilcox <willy@infradead.org>
    cc: netdev@vger.kernel.org
    ---
    include/linux/socket.h | 3 +++
    net/socket.c | 7 +++++++
    2 files changed, 10 insertions(+)

    diff --git a/include/linux/socket.h b/include/linux/socket.h
    index 13c3a237b9c9..c2fa0f800999 100644
    --- a/include/linux/socket.h
    +++ b/include/linux/socket.h
    @@ -327,6 +327,7 @@ struct ucred {
    */

    #define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */
    +#define MSG_SPLICE_PAGES 0x8000000 /* Splice the pages from the iterator in sendmsg() */
    #define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */
    #define MSG_CMSG_CLOEXEC 0x40000000 /* Set close_on_exec for file
    descriptor received through
    @@ -337,6 +338,8 @@ struct ucred {
    #define MSG_CMSG_COMPAT 0 /* We never have 32 bit fixups */
    #endif

    +/* Flags to be cleared on entry by sendmsg, recvmsg, sendmmsg and recvmmsg syscalls */
    +#define MSG_INTERNAL_FLAGS (MSG_SPLICE_PAGES)

    /* Setsockoptions(2) level. Thanks to BSD these must match IPPROTO_xxx */
    #define SOL_IP 0
    diff --git a/net/socket.c b/net/socket.c
    index 6bae8ce7059e..dfb912bbed62 100644
    --- a/net/socket.c
    +++ b/net/socket.c
    @@ -2139,6 +2139,7 @@ int __sys_sendto(int fd, void __user *buff, size_t len, unsigned int flags,
    msg.msg_name = (struct sockaddr *)&address;
    msg.msg_namelen = addr_len;
    }
    + flags &= ~MSG_INTERNAL_FLAGS;
    if (sock->file->f_flags & O_NONBLOCK)
    flags |= MSG_DONTWAIT;
    msg.msg_flags = flags;
    @@ -2192,6 +2193,7 @@ int __sys_recvfrom(int fd, void __user *ubuf, size_t size, unsigned int flags,
    if (!sock)
    goto out;

    + flags &= ~MSG_INTERNAL_FLAGS;
    if (sock->file->f_flags & O_NONBLOCK)
    flags |= MSG_DONTWAIT;
    err = sock_recvmsg(sock, &msg, flags);
    @@ -2579,6 +2581,7 @@ long __sys_sendmsg(int fd, struct user_msghdr __user *msg, unsigned int flags,

    if (forbid_cmsg_compat && (flags & MSG_CMSG_COMPAT))
    return -EINVAL;
    + flags &= ~MSG_INTERNAL_FLAGS;

    sock = sockfd_lookup_light(fd, &err, &fput_needed);
    if (!sock)
    @@ -2627,6 +2630,7 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
    entry = mmsg;
    compat_entry = (struct compat_mmsghdr __user *)mmsg;
    err = 0;
    + flags &= ~MSG_INTERNAL_FLAGS;
    flags |= MSG_BATCH;

    while (datagrams < vlen) {
    @@ -2775,6 +2779,7 @@ long __sys_recvmsg_sock(struct socket *sock, struct msghdr *msg,
    struct user_msghdr __user *umsg,
    struct sockaddr __user *uaddr, unsigned int flags)
    {
    + flags &= ~MSG_INTERNAL_FLAGS;
    return ____sys_recvmsg(sock, msg, umsg, uaddr, flags, 0);
    }

    @@ -2787,6 +2792,7 @@ long __sys_recvmsg(int fd, struct user_msghdr __user *msg, unsigned int flags,

    if (forbid_cmsg_compat && (flags & MSG_CMSG_COMPAT))
    return -EINVAL;
    + flags &= ~MSG_INTERNAL_FLAGS;

    sock = sockfd_lookup_light(fd, &err, &fput_needed);
    if (!sock)
    @@ -2839,6 +2845,7 @@ static int do_recvmmsg(int fd, struct mmsghdr __user *mmsg,
    goto out_put;
    }
    }
    + flags &= ~MSG_INTERNAL_FLAGS;

    entry = mmsg;
    compat_entry = (struct compat_mmsghdr __user *)mmsg;
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