Commit 4a93d1ee authored Feb 05, 2026 by Stefan Metzmacher Committed by Steve French Feb 08, 2026

smb: client: correct value for smbd_max_fragmented_recv_size



When we download a file without rdma offload or get
a large directly enumeration from the server,
the server might want to send up to smbd_max_fragmented_recv_size
bytes, but if it is too large all our recv buffers
might already be moved to the recv_io.reassembly.list
and we're no longer able to grant recv credits.

The maximum fragmented upper-layer payload receive size supported

Assume max_payload_per_credit is
smbd_max_receive_size - 24 = 1340

The maximum number would be
smbd_receive_credit_max * max_payload_per_credit

                      1340 * 255 = 341700 (0x536C4)

The minimum value from the spec is 131072 (0x20000)

For now we use the logic we used in ksmbd before:
                (1364 * 255) / 2 = 173910 (0x2A756)

Fixes: 03bee01d ("CIFS: SMBD: Add SMB Direct protocol initial values and constants")
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

parent 77ffbcac

fs/smb/client/smbdirect.c

+17 −2

Original line number	Diff line number	Diff line
		@@ -101,8 +101,23 @@ int smbd_send_credit_target = 255;
		/* The maximum single message size can be sent to remote peer */
		int smbd_max_send_size = 1364;

		/* The maximum fragmented upper-layer payload receive size supported */
		int smbd_max_fragmented_recv_size = 1024 * 1024;
		/*
		* The maximum fragmented upper-layer payload receive size supported
		*
		* Assume max_payload_per_credit is
		* smbd_max_receive_size - 24 = 1340
		*
		* The maximum number would be
		* smbd_receive_credit_max * max_payload_per_credit
		*
		* 1340 * 255 = 341700 (0x536C4)
		*
		* The minimum value from the spec is 131072 (0x20000)
		*
		* For now we use the logic we used in ksmbd before:
		* (1364 * 255) / 2 = 173910 (0x2A756)
		*/
		int smbd_max_fragmented_recv_size = (1364 * 255) / 2;

		/* The maximum single-message size which can be received */
		int smbd_max_receive_size = 1364;