[PATCH net-next v6 4/6] net: devmem: add SO_DEVMEM_AUTORELEASE for autorelease control

[Bobby Eshleman <bobbyeshleman@gmail.com>]

From: Bobby Eshleman <bobbyeshleman@meta.com>

Add SO_DEVMEM_AUTORELEASE socket option to allow applications to
control token release behavior on a per-socket basis.

The socket option accepts boolean values (0 or 1):
- 1 (true): outstanding tokens are automatically released when the
  socket closes
- 0 (false): outstanding tokens are released when the dmabuf is unbound

The option can only be changed when the socket has no outstanding
tokens, enforced by checking:
1. The frags xarray is empty (no tokens in autorelease mode)
2. The outstanding_urefs counter is zero (no tokens in manual mode)

This restriction prevents inconsistent token tracking state between
acquisition and release calls. If either condition fails, setsockopt
returns -EBUSY.

The default state is autorelease off.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
 include/uapi/asm-generic/socket.h       |  2 ++
 net/core/sock.c                         | 51 +++++++++++++++++++++++++++++++++
 net/ipv4/tcp.c                          |  2 +-
 tools/include/uapi/asm-generic/socket.h |  2 ++
 4 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 53b5a8c002b1..59302318bb34 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -150,6 +150,8 @@
 #define SO_INQ			84
 #define SCM_INQ			SO_INQ
 
+#define SO_DEVMEM_AUTORELEASE	85
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/net/core/sock.c b/net/core/sock.c
index 465645c1d74f..27af476f3cd3 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1160,6 +1160,46 @@ sock_devmem_dontneed_autorelease(struct sock *sk, struct dmabuf_token *tokens,
 	return ret;
 }
 
+static noinline_for_stack int
+sock_devmem_set_autorelease(struct sock *sk, sockptr_t optval, unsigned int optlen)
+{
+	int val;
+
+	if (!sk_is_tcp(sk))
+		return -EBADF;
+
+	if (optlen < sizeof(int))
+		return -EINVAL;
+
+	if (copy_from_sockptr(&val, optval, sizeof(val)))
+		return -EFAULT;
+
+	/* Validate that val is 0 or 1 */
+	if (val != 0 && val != 1)
+		return -EINVAL;
+
+	sockopt_lock_sock(sk);
+
+	/* Can only change autorelease if:
+	 * 1. No tokens in the frags xarray (autorelease mode)
+	 * 2. No outstanding urefs (manual release mode)
+	 */
+	if (!xa_empty(&sk->sk_devmem_info.frags)) {
+		sockopt_release_sock(sk);
+		return -EBUSY;
+	}
+
+	if (atomic_read(&sk->sk_devmem_info.outstanding_urefs) > 0) {
+		sockopt_release_sock(sk);
+		return -EBUSY;
+	}
+
+	sk->sk_devmem_info.autorelease = !!val;
+
+	sockopt_release_sock(sk);
+	return 0;
+}
+
 static noinline_for_stack int
 sock_devmem_dontneed(struct sock *sk, sockptr_t optval, unsigned int optlen)
 {
@@ -1351,6 +1391,9 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
 #ifdef CONFIG_PAGE_POOL
 	case SO_DEVMEM_DONTNEED:
 		return sock_devmem_dontneed(sk, optval, optlen);
+
+	case SO_DEVMEM_AUTORELEASE:
+		return sock_devmem_set_autorelease(sk, optval, optlen);
 #endif
 	case SO_SNDTIMEO_OLD:
 	case SO_SNDTIMEO_NEW:
@@ -2208,6 +2251,14 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
 		v.val = READ_ONCE(sk->sk_txrehash);
 		break;
 
+#ifdef CONFIG_PAGE_POOL
+	case SO_DEVMEM_AUTORELEASE:
+		if (!sk_is_tcp(sk))
+			return -EBADF;
+		v.val = sk->sk_devmem_info.autorelease;
+		break;
+#endif
+
 	default:
 		/* We implement the SO_SNDLOWAT etc to not be settable
 		 * (1003.1g 7).
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 052875c1b547..8226ba892b36 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -496,7 +496,7 @@ void tcp_init_sock(struct sock *sk)
 	xa_init_flags(&sk->sk_devmem_info.frags, XA_FLAGS_ALLOC1);
 	sk->sk_devmem_info.binding = NULL;
 	atomic_set(&sk->sk_devmem_info.outstanding_urefs, 0);
-	sk->sk_devmem_info.autorelease = true;
+	sk->sk_devmem_info.autorelease = false;
 }
 EXPORT_IPV6_MOD(tcp_init_sock);
 
diff --git a/tools/include/uapi/asm-generic/socket.h b/tools/include/uapi/asm-generic/socket.h
index f333a0ac4ee4..9710a3d7cc4d 100644
--- a/tools/include/uapi/asm-generic/socket.h
+++ b/tools/include/uapi/asm-generic/socket.h
@@ -147,6 +147,8 @@
 
 #define SO_PASSRIGHTS		83
 
+#define SO_DEVMEM_AUTORELEASE	85
+
 #if !defined(__KERNEL__)
 
 #if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))

-- 
2.47.3