cifs: Provide the capability to extract from ITER_FOLIOQ to RDMA SGEs

Make smb_extract_iter_to_rdma() extract page fragments from an ITER_FOLIOQ
iterator into RDMA SGEs.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Enzo Matsumiya <ematsumiya@suse.de>
cc: linux-cifs@vger.kernel.org
Link: https://lore.kernel.org/r/20240814203850.2240469-15-dhowells@redhat.com/ # v2
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/smb/client/smbdirect.c

@@ -6,6 +6,7 @@
  */
 #include <linux/module.h>
 #include <linux/highmem.h>
+#include <linux/folio_queue.h>
 #include "smbdirect.h"
 #include "cifs_debug.h"
 #include "cifsproto.h"
@@ -2463,6 +2464,8 @@ static ssize_t smb_extract_bvec_to_rdma(struct iov_iter *iter,
 		start = 0;
 	}
 
+	if (ret > 0)
+		iov_iter_advance(iter, ret);
 	return ret;
 }
 
@@ -2519,6 +2522,65 @@ static ssize_t smb_extract_kvec_to_rdma(struct iov_iter *iter,
 		start = 0;
 	}
 
+	if (ret > 0)
+		iov_iter_advance(iter, ret);
+	return ret;
+}
+
+/*
+ * Extract folio fragments from a FOLIOQ-class iterator and add them to an RDMA
+ * list.  The folios are not pinned.
+ */
+static ssize_t smb_extract_folioq_to_rdma(struct iov_iter *iter,
+					  struct smb_extract_to_rdma *rdma,
+					  ssize_t maxsize)
+{
+	const struct folio_queue *folioq = iter->folioq;
+	unsigned int slot = iter->folioq_slot;
+	ssize_t ret = 0;
+	size_t offset = iter->iov_offset;
+
+	BUG_ON(!folioq);
+
+	if (slot >= folioq_nr_slots(folioq)) {
+		folioq = folioq->next;
+		if (WARN_ON_ONCE(!folioq))
+			return -EIO;
+		slot = 0;
+	}
+
+	do {
+		struct folio *folio = folioq_folio(folioq, slot);
+		size_t fsize = folioq_folio_size(folioq, slot);
+
+		if (offset < fsize) {
+			size_t part = umin(maxsize - ret, fsize - offset);
+
+			if (!smb_set_sge(rdma, folio_page(folio, 0), offset, part))
+				return -EIO;
+
+			offset += part;
+			ret += part;
+		}
+
+		if (offset >= fsize) {
+			offset = 0;
+			slot++;
+			if (slot >= folioq_nr_slots(folioq)) {
+				if (!folioq->next) {
+					WARN_ON_ONCE(ret < iter->count);
+					break;
+				}
+				folioq = folioq->next;
+				slot = 0;
+			}
+		}
+	} while (rdma->nr_sge < rdma->max_sge || maxsize > 0);
+
+	iter->folioq = folioq;
+	iter->folioq_slot = slot;
+	iter->iov_offset = offset;
+	iter->count -= ret;
 	return ret;
 }
 
@@ -2563,6 +2625,8 @@ static ssize_t smb_extract_xarray_to_rdma(struct iov_iter *iter,
 	}
 
 	rcu_read_unlock();
+	if (ret > 0)
+		iov_iter_advance(iter, ret);
 	return ret;
 }
 
@@ -2590,6 +2654,9 @@ static ssize_t smb_extract_iter_to_rdma(struct iov_iter *iter, size_t len,
 	case ITER_KVEC:
 		ret = smb_extract_kvec_to_rdma(iter, rdma, len);
 		break;
+	case ITER_FOLIOQ:
+		ret = smb_extract_folioq_to_rdma(iter, rdma, len);
+		break;
 	case ITER_XARRAY:
 		ret = smb_extract_xarray_to_rdma(iter, rdma, len);
 		break;
@@ -2598,9 +2665,7 @@ static ssize_t smb_extract_iter_to_rdma(struct iov_iter *iter, size_t len,
 		return -EIO;
 	}
 
-	if (ret > 0) {
-		iov_iter_advance(iter, ret);
-	} else if (ret < 0) {
+	if (ret < 0) {
 		while (rdma->nr_sge > before) {
 			struct ib_sge *sge = &rdma->sge[rdma->nr_sge--];