Add an interface for the user to notify the kernel that it is done
reading the NET_RX dmabuf pages returned as cmsg. The kernel will
drop the reference on the NET_RX pages to make them available for
re-use.

Signed-off-by: Willem de Bruijn <will...@google.com>
Signed-off-by: Kaiyuan Zhang <kaiyu...@google.com>

Signed-off-by: Mina Almasry <almasrym...@google.com>
---
 include/uapi/asm-generic/socket.h |  1 +
 include/uapi/linux/uio.h          |  4 ++++
 net/core/sock.c                   | 36 +++++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/include/uapi/asm-generic/socket.h 
b/include/uapi/asm-generic/socket.h
index aacb97f16b78..eb93b43394d4 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -135,6 +135,7 @@
 #define SO_PASSPIDFD           76
 #define SO_PEERPIDFD           77
 
+#define SO_DEVMEM_DONTNEED     97
 #define SO_DEVMEM_HEADER       98
 #define SCM_DEVMEM_HEADER      SO_DEVMEM_HEADER
 #define SO_DEVMEM_OFFSET       99
diff --git a/include/uapi/linux/uio.h b/include/uapi/linux/uio.h
index ae94763b1963..71314bf41590 100644
--- a/include/uapi/linux/uio.h
+++ b/include/uapi/linux/uio.h
@@ -26,6 +26,10 @@ struct cmsg_devmem {
        __u32 frag_token;
 };
 
+struct devmemtoken {
+       __u32 token_start;
+       __u32 token_count;
+};
 /*
  *     UIO_MAXIOV shall be at least 16 1003.1g (5.4.1.1)
  */
diff --git a/net/core/sock.c b/net/core/sock.c
index ab1e8d1bd5a1..2736b770a399 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1049,6 +1049,39 @@ static int sock_reserve_memory(struct sock *sk, int 
bytes)
        return 0;
 }
 
+static noinline_for_stack int
+sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
+{
+       struct devmemtoken tokens[128];
+       unsigned int num_tokens, i, j;
+       int ret;
+
+       if (sk->sk_type != SOCK_STREAM || sk->sk_protocol != IPPROTO_TCP)
+               return -EBADF;
+
+       if (optlen % sizeof(struct devmemtoken) || optlen > sizeof(tokens))
+               return -EINVAL;
+
+       num_tokens = optlen / sizeof(struct devmemtoken);
+       if (copy_from_sockptr(tokens, optval, optlen))
+               return -EFAULT;
+
+       ret = 0;
+       for (i = 0; i < num_tokens; i++) {
+               for (j = 0; j < tokens[i].token_count; j++) {
+                       struct page *page = xa_erase(&sk->sk_user_pages,
+                                                    tokens[i].token_start + j);
+
+                       if (page) {
+                               page_pool_page_put_many(page, 1);
+                               ret++;
+                       }
+               }
+       }
+
+       return ret;
+}
+
 void sockopt_lock_sock(struct sock *sk)
 {
        /* When current->bpf_ctx is set, the setsockopt is called from
@@ -1528,6 +1561,9 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
                WRITE_ONCE(sk->sk_txrehash, (u8)val);
                break;
 
+       case SO_DEVMEM_DONTNEED:
+               ret = sock_devmem_dontneed(sk, optval, optlen);
+               break;
        default:
                ret = -ENOPROTOOPT;
                break;
-- 
2.41.0.640.ga95def55d0-goog

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