From e679ac4bb80574b03b804c98a825bf851d92fc8d Mon Sep 17 00:00:00 2001 From: Chuck Lever Date: Tue, 8 Sep 2026 09:42:27 -0400 Subject: [PATCH] SUNRPC: Add svcxdr_encode_opaque_payload() The encoder functions that xdrgen emits handle a variable-length opaque with xdr_stream_encode_opaque(), which copies the opaque content into the RPC buffer. On the server, an NFS READ payload already resides in the pages of rqstp->rq_res, placed there by an underlying file system read. Copying that payload into the RPC Reply buffer adds a data copy on every READ and prevents a transport capable of direct data placement from conveying the payload separately from the rest of the Reply. Add a helper that encodes a page-resident opaque by reference: it encodes the length, inserts the payload pages into the XDR stream, then marks the byte range as a result payload. Generated code calls this helper, so its parameters are limited to the xdr_stream and the payload length. It recovers the svc_rqst with svcxdr_rqst(), and takes the reply's page array from the stream's buffer. Acked-by: Jeff Layton Link: https://patch.msgid.link/20260908134234.512312-4-cel@kernel.org Signed-off-by: Chuck Lever --- include/linux/sunrpc/svc.h | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h index e69aeb864a8d..7950a2ce0a27 100644 --- a/include/linux/sunrpc/svc.h +++ b/include/linux/sunrpc/svc.h @@ -608,6 +608,41 @@ static inline void svcxdr_encode_opaque_pages(struct svc_rqst *rqstp, xdr->page_ptr = rqstp->rq_next_page - 1; } +/** + * svcxdr_encode_opaque_payload - Encode a page-resident opaque data item + * @xdr: xdr_stream to be updated + * @len: number of octets of content in the data item + * + * Context: Process context. @xdr must have been initialized by + * svcxdr_init_encode() and still be positioned in the reply + * head. + * + * Return: + * %true: Success + * %false: The reply head cannot hold the length prefix and XDR + * padding, or the transport could not accommodate the result payload + */ +static inline bool svcxdr_encode_opaque_payload(struct xdr_stream *xdr, u32 len) +{ + struct svc_rqst *rqstp = svcxdr_rqst(xdr); + struct xdr_buf *buf = xdr->buf; + + /* + * The length prefix and any pad word must land in the reply + * head. A prefix that spills into the first Reply page lands + * on the payload itself, and xdr_write_pages() BUGs when the + * pad word does not fit. + */ + if ((xdr->end - xdr->p) * XDR_UNIT < XDR_UNIT + xdr_pad_size(len)) + return false; + if (xdr_stream_encode_u32(xdr, len) < 0) + return false; + svcxdr_encode_opaque_pages(rqstp, xdr, buf->pages, buf->page_base, len); + if (svc_encode_result_payload(rqstp, buf->head->iov_len, len) < 0) + return false; + return true; +} + /** * svcxdr_set_auth_slack - * @rqstp: RPC transaction