netfs: Abstract out a rolling folio buffer implementation

A rolling buffer is a series of folios held in a list of folio_queues.  New
folios and folio_queue structs may be inserted at the head simultaneously
with spent ones being removed from the tail without the need for locking.

The rolling buffer includes an iov_iter and it has to be careful managing
this as the list of folio_queues is extended such that an oops doesn't
incurred because the iterator was pointing to the end of a folio_queue
segment that got appended to and then removed.

We need to use the mechanism twice, once for read and once for write, and,
in future patches, we will use a second rolling buffer to handle bounce
buffering for content encryption.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241216204124.3752367-6-dhowells@redhat.com
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/netfs/read_retry.c b/fs/netfs/read_retry.c
index 21b4a54e545e1..0983234c2183f 100644
--- a/fs/netfs/read_retry.c
+++ b/fs/netfs/read_retry.c
@@ -245,7 +245,7 @@ void netfs_unlock_abandoned_read_pages(struct netfs_io_request *rreq)
 {
 	struct folio_queue *p;
 
-	for (p = rreq->buffer; p; p = p->next) {
+	for (p = rreq->buffer.tail; p; p = p->next) {
 		for (int slot = 0; slot < folioq_count(p); slot++) {
 			struct folio *folio = folioq_folio(p, slot);