Add support for ITER_BVECQ to smbdirect_map_sges_from_iter().

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Stefan Metzmacher <metze@samba.org>
cc: Paulo Alcantara <pc@manguebit.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: Christoph Hellwig <hch@infradead.org>
cc: Steve French <sfrench@samba.org>
cc: Shyam Prasad N <sprasad@microsoft.com>
cc: Tom Talpey <tom@talpey.com>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
---
 fs/smb/smbdirect/connection.c | 66 +++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/fs/smb/smbdirect/connection.c b/fs/smb/smbdirect/connection.c
index 8adf58097534..4d2a1700104e 100644
--- a/fs/smb/smbdirect/connection.c
+++ b/fs/smb/smbdirect/connection.c
@@ -5,6 +5,7 @@
  */
 
 #include "internal.h"
+#include <linux/bvecq.h>
 #include <linux/folio_queue.h>
 
 struct smbdirect_map_sges {
@@ -2006,6 +2007,68 @@ static ssize_t smbdirect_map_sges_from_bvec(struct iov_iter *iter,
 	return ret;
 }
 
+/*
+ * Extract memory fragments from a BVECQ-class iterator and add them to an RDMA
+ * list.  The fragments are not pinned.
+ */
+static ssize_t smbdirect_map_sges_from_bvecq(struct iov_iter *iter,
+					     struct smbdirect_map_sges *state,
+					     ssize_t maxsize)
+{
+	const struct bvecq *bq = iter->bvecq;
+	unsigned int slot = iter->bvecq_slot;
+	ssize_t extracted = 0;
+	size_t offset = iter->iov_offset;
+
+	maxsize = umin(maxsize, iov_iter_count(iter));
+
+	do {
+		struct bio_vec *bv;
+		size_t bsize;
+
+		while (slot >= bq->nr_slots) {
+			if (!bq->next) {
+				if (WARN_ON_ONCE(maxsize > 0))
+					return -EIO;
+				goto out;
+			}
+			bq = bq->next;
+			slot = 0;
+		}
+
+		bv = &bq->bv[slot];
+		bsize = bv->bv_len;
+
+		if (offset < bsize) {
+			size_t part = umin(maxsize, bsize - offset);
+			bool ok;
+
+			ok = smbdirect_map_sges_single_page(state,
+							    bv->bv_page,
+							    bv->bv_offset + offset,
+							    part);
+			if (!ok)
+				return -EIO;
+
+			offset += part;
+			extracted += part;
+			maxsize -= part;
+		}
+
+		if (offset >= bsize) {
+			offset = 0;
+			slot++;
+		}
+	} while (state->num_sge < state->max_sge && maxsize > 0);
+
+out:
+	iter->bvecq = bq;
+	iter->bvecq_slot = slot;
+	iter->iov_offset = offset;
+	iter->count -= extracted;
+	return extracted;
+}
+
 /*
  * Extract fragments from a KVEC-class iterator and add them to an ib_sge list.
  * This can deal with vmalloc'd buffers as well as kmalloc'd or static buffers.
@@ -2155,6 +2218,9 @@ static ssize_t smbdirect_map_sges_from_iter(struct iov_iter *iter, size_t len,
 	case ITER_BVEC:
 		ret = smbdirect_map_sges_from_bvec(iter, state, len);
 		break;
+	case ITER_BVECQ:
+		ret = smbdirect_map_sges_from_bvecq(iter, state, len);
+		break;
 	case ITER_KVEC:
 		ret = smbdirect_map_sges_from_kvec(iter, state, len);
 		break;