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smb: client: correct value for smbd_max_fragmented_recv_size

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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: 03bee01d62 ("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>
This commit is contained in:
Stefan Metzmacher
2026-02-05 17:14:14 +01:00
committed by Steve French
parent 77ffbcac4e
commit 4a93d1ee2d
1 changed files with 17 additions and 2 deletions
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19
fs/smb/client/smbdirect.c
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@@ -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;