[RFC 08/19] netfs: refactor netfs_clear_unread()

[Jeffle Xu <jefflexu@linux.alibaba.com>]

In demand-read case, the input folio of netfs API is may not the page
cache inside the address space of the netfs file. Instead it may be just
a temporary page used to contain the data.

In this case, use bvec based iov_iter.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/netfs/read_helper.c | 33 +++++++++++++++++++++++++++------
 include/linux/netfs.h  |  2 ++
 2 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 26fa688f6300..04d0cc2fca83 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -157,6 +157,18 @@ static void __netfs_put_subrequest(struct netfs_read_subrequest *subreq,
 	netfs_put_read_request(rreq, was_async);
 }
 
+static void netfs_init_iov_iter_bvec(struct netfs_read_subrequest *subreq,
+				     struct iov_iter *iter)
+{
+	struct bio_vec *bvec = &subreq->bvec;
+
+	bvec->bv_page	= folio_page(subreq->rreq->folio, 0);
+	bvec->bv_offset	= subreq->start + subreq->transferred;
+	bvec->bv_len	= subreq->len   - subreq->transferred;
+
+	iov_iter_bvec(iter, READ, bvec, 1, bvec->bv_len);
+}
+
 /*
  * Clear the unread part of an I/O request.
  */
@@ -164,9 +176,14 @@ static void netfs_clear_unread(struct netfs_read_subrequest *subreq)
 {
 	struct iov_iter iter;
 
-	iov_iter_xarray(&iter, READ, &subreq->rreq->mapping->i_pages,
-			subreq->start + subreq->transferred,
-			subreq->len   - subreq->transferred);
+	if (subreq->rreq->type == NETFS_TYPE_CACHE) {
+		iov_iter_xarray(&iter, READ, &subreq->rreq->mapping->i_pages,
+				subreq->start + subreq->transferred,
+				subreq->len   - subreq->transferred);
+	} else { /* type == NETFS_TYPE_DEMAND */
+		netfs_init_iov_iter_bvec(subreq, &iter);
+	}
+
 	iov_iter_zero(iov_iter_count(&iter), &iter);
 }
 
@@ -190,9 +207,13 @@ static void netfs_read_from_cache(struct netfs_read_request *rreq,
 	struct iov_iter iter;
 
 	netfs_stat(&netfs_n_rh_read);
-	iov_iter_xarray(&iter, READ, &rreq->mapping->i_pages,
-			subreq->start + subreq->transferred,
-			subreq->len   - subreq->transferred);
+	if (subreq->rreq->type == NETFS_TYPE_CACHE) {
+		iov_iter_xarray(&iter, READ, &subreq->rreq->mapping->i_pages,
+				subreq->start + subreq->transferred,
+				subreq->len   - subreq->transferred);
+	} else { /* type == NETFS_TYPE_DEMAND */
+		netfs_init_iov_iter_bvec(subreq, &iter);
+	}
 
 	cres->ops->read(cres, subreq->start, &iter, read_hole,
 			netfs_cache_read_terminated, subreq);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index de6948bcc80a..5f45eb31defd 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -17,6 +17,7 @@
 #include <linux/workqueue.h>
 #include <linux/fs.h>
 #include <linux/pagemap.h>
+#include <linux/bvec.h>
 
 /*
  * Overload PG_private_2 to give us PG_fscache - this is used to indicate that
@@ -146,6 +147,7 @@ struct netfs_read_subrequest {
 #define NETFS_SREQ_SHORT_READ		2	/* Set if there was a short read from the cache */
 #define NETFS_SREQ_SEEK_DATA_READ	3	/* Set if ->read() should SEEK_DATA first */
 #define NETFS_SREQ_NO_PROGRESS		4	/* Set if we didn't manage to read any data */
+	struct bio_vec 		bvec;
 };
 
 enum netfs_read_request_type {
-- 
2.27.0