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 <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
cc: Jeff Layton <[email protected]>
cc: [email protected]
cc: [email protected]
Signed-off-by: Christian Brauner <[email protected]>

1 files changed, 0 insertions, 147 deletions

diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index afe032551de5..4249715f4171 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -8,153 +8,6 @@
 #include <linux/swap.h>
 #include "internal.h"
 
-/**
- * netfs_folioq_alloc - Allocate a folio_queue struct
- * @rreq_id: Associated debugging ID for tracing purposes
- * @gfp: Allocation constraints
- * @trace: Trace tag to indicate the purpose of the allocation
- *
- * Allocate, initialise and account the folio_queue struct and log a trace line
- * to mark the allocation.
- */
-struct folio_queue *netfs_folioq_alloc(unsigned int rreq_id, gfp_t gfp,
-				       unsigned int /*enum netfs_folioq_trace*/ trace)
-{
-	static atomic_t debug_ids;
-	struct folio_queue *fq;
-
-	fq = kmalloc(sizeof(*fq), gfp);
-	if (fq) {
-		netfs_stat(&netfs_n_folioq);
-		folioq_init(fq, rreq_id);
-		fq->debug_id = atomic_inc_return(&debug_ids);
-		trace_netfs_folioq(fq, trace);
-	}
-	return fq;
-}
-EXPORT_SYMBOL(netfs_folioq_alloc);
-
-/**
- * netfs_folioq_free - Free a folio_queue struct
- * @folioq: The object to free
- * @trace: Trace tag to indicate which free
- *
- * Free and unaccount the folio_queue struct.
- */
-void netfs_folioq_free(struct folio_queue *folioq,
-		       unsigned int /*enum netfs_trace_folioq*/ trace)
-{
-	trace_netfs_folioq(folioq, trace);
-	netfs_stat_d(&netfs_n_folioq);
-	kfree(folioq);
-}
-EXPORT_SYMBOL(netfs_folioq_free);
-
-/*
- * Make sure there's space in the rolling queue.
- */
-struct folio_queue *netfs_buffer_make_space(struct netfs_io_request *rreq,
-					    enum netfs_folioq_trace trace)
-{
-	struct folio_queue *tail = rreq->buffer_tail, *prev;
-	unsigned int prev_nr_slots = 0;
-
-	if (WARN_ON_ONCE(!rreq->buffer && tail) ||
-	    WARN_ON_ONCE(rreq->buffer && !tail))
-		return ERR_PTR(-EIO);
-
-	prev = tail;
-	if (prev) {
-		if (!folioq_full(tail))
-			return tail;
-		prev_nr_slots = folioq_nr_slots(tail);
-	}
-
-	tail = netfs_folioq_alloc(rreq->debug_id, GFP_NOFS, trace);
-	if (!tail)
-		return ERR_PTR(-ENOMEM);
-	tail->prev = prev;
-	if (prev)
-		/* [!] NOTE: After we set prev->next, the consumer is entirely
-		 * at liberty to delete prev.
-		 */
-		WRITE_ONCE(prev->next, tail);
-
-	rreq->buffer_tail = tail;
-	if (!rreq->buffer) {
-		rreq->buffer = tail;
-		iov_iter_folio_queue(&rreq->io_iter, ITER_SOURCE, tail, 0, 0, 0);
-	} else {
-		/* Make sure we don't leave the master iterator pointing to a
-		 * block that might get immediately consumed.
-		 */
-		if (rreq->io_iter.folioq == prev &&
-		    rreq->io_iter.folioq_slot == prev_nr_slots) {
-			rreq->io_iter.folioq = tail;
-			rreq->io_iter.folioq_slot = 0;
-		}
-	}
-	rreq->buffer_tail_slot = 0;
-	return tail;
-}
-
-/*
- * Append a folio to the rolling queue.
- */
-int netfs_buffer_append_folio(struct netfs_io_request *rreq, struct folio *folio,
-			      bool needs_put)
-{
-	struct folio_queue *tail;
-	unsigned int slot, order = folio_order(folio);
-
-	tail = netfs_buffer_make_space(rreq, netfs_trace_folioq_alloc_append_folio);
-	if (IS_ERR(tail))
-		return PTR_ERR(tail);
-
-	rreq->io_iter.count += PAGE_SIZE << order;
-
-	slot = folioq_append(tail, folio);
-	/* Store the counter after setting the slot. */
-	smp_store_release(&rreq->buffer_tail_slot, slot);
-	return 0;
-}
-
-/*
- * Delete the head of a rolling queue.
- */
-struct folio_queue *netfs_delete_buffer_head(struct netfs_io_request *wreq)
-{
-	struct folio_queue *head = wreq->buffer, *next = head->next;
-
-	if (next)
-		next->prev = NULL;
-	netfs_folioq_free(head, netfs_trace_folioq_delete);
-	wreq->buffer = next;
-	return next;
-}
-
-/*
- * Clear out a rolling queue.
- */
-void netfs_clear_buffer(struct netfs_io_request *rreq)
-{
-	struct folio_queue *p;
-
-	while ((p = rreq->buffer)) {
-		rreq->buffer = p->next;
-		for (int slot = 0; slot < folioq_count(p); slot++) {
-			struct folio *folio = folioq_folio(p, slot);
-			if (!folio)
-				continue;
-			if (folioq_is_marked(p, slot)) {
-				trace_netfs_folio(folio, netfs_folio_trace_put);
-				folio_put(folio);
-			}
-		}
-		netfs_folioq_free(p, netfs_trace_folioq_clear);
-	}
-}
-
 /*
  * Reset the subrequest iterator to refer just to the region remaining to be
  * read.  The iterator may or may not have been advanced by socket ops or