Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 972 insertions, 0 deletions

diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
new file mode 100644
index 000000000..8ffc40e84
--- /dev/null
+++ b/fs/cachefiles/rdwr.c
@@ -0,0 +1,972 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Storage object read/write
+ *
+ * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/mount.h>
+#include <linux/slab.h>
+#include <linux/file.h>
+#include <linux/swap.h>
+#include "internal.h"
+
+/*
+ * detect wake up events generated by the unlocking of pages in which we're
+ * interested
+ * - we use this to detect read completion of backing pages
+ * - the caller holds the waitqueue lock
+ */
+static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
+				  int sync, void *_key)
+{
+	struct cachefiles_one_read *monitor =
+		container_of(wait, struct cachefiles_one_read, monitor);
+	struct cachefiles_object *object;
+	struct fscache_retrieval *op = monitor->op;
+	struct wait_page_key *key = _key;
+	struct page *page = wait->private;
+
+	ASSERT(key);
+
+	_enter("{%lu},%u,%d,{%p,%u}",
+	       monitor->netfs_page->index, mode, sync,
+	       key->page, key->bit_nr);
+
+	if (key->page != page || key->bit_nr != PG_locked)
+		return 0;
+
+	_debug("--- monitor %p %lx ---", page, page->flags);
+
+	if (!PageUptodate(page) && !PageError(page)) {
+		/* unlocked, not uptodate and not erronous? */
+		_debug("page probably truncated");
+	}
+
+	/* remove from the waitqueue */
+	list_del(&wait->entry);
+
+	/* move onto the action list and queue for FS-Cache thread pool */
+	ASSERT(op);
+
+	/* We need to temporarily bump the usage count as we don't own a ref
+	 * here otherwise cachefiles_read_copier() may free the op between the
+	 * monitor being enqueued on the op->to_do list and the op getting
+	 * enqueued on the work queue.
+	 */
+	fscache_get_retrieval(op);
+
+	object = container_of(op->op.object, struct cachefiles_object, fscache);
+	spin_lock(&object->work_lock);
+	list_add_tail(&monitor->op_link, &op->to_do);
+	fscache_enqueue_retrieval(op);
+	spin_unlock(&object->work_lock);
+
+	fscache_put_retrieval(op);
+	return 0;
+}
+
+/*
+ * handle a probably truncated page
+ * - check to see if the page is still relevant and reissue the read if
+ *   possible
+ * - return -EIO on error, -ENODATA if the page is gone, -EINPROGRESS if we
+ *   must wait again and 0 if successful
+ */
+static int cachefiles_read_reissue(struct cachefiles_object *object,
+				   struct cachefiles_one_read *monitor)
+{
+	struct address_space *bmapping = d_backing_inode(object->backer)->i_mapping;
+	struct page *backpage = monitor->back_page, *backpage2;
+	int ret;
+
+	_enter("{ino=%lx},{%lx,%lx}",
+	       d_backing_inode(object->backer)->i_ino,
+	       backpage->index, backpage->flags);
+
+	/* skip if the page was truncated away completely */
+	if (backpage->mapping != bmapping) {
+		_leave(" = -ENODATA [mapping]");
+		return -ENODATA;
+	}
+
+	backpage2 = find_get_page(bmapping, backpage->index);
+	if (!backpage2) {
+		_leave(" = -ENODATA [gone]");
+		return -ENODATA;
+	}
+
+	if (backpage != backpage2) {
+		put_page(backpage2);
+		_leave(" = -ENODATA [different]");
+		return -ENODATA;
+	}
+
+	/* the page is still there and we already have a ref on it, so we don't
+	 * need a second */
+	put_page(backpage2);
+
+	INIT_LIST_HEAD(&monitor->op_link);
+	add_page_wait_queue(backpage, &monitor->monitor);
+
+	if (trylock_page(backpage)) {
+		ret = -EIO;
+		if (PageError(backpage))
+			goto unlock_discard;
+		ret = 0;
+		if (PageUptodate(backpage))
+			goto unlock_discard;
+
+		_debug("reissue read");
+		ret = bmapping->a_ops->readpage(NULL, backpage);
+		if (ret < 0)
+			goto discard;
+	}
+
+	/* but the page may have been read before the monitor was installed, so
+	 * the monitor may miss the event - so we have to ensure that we do get
+	 * one in such a case */
+	if (trylock_page(backpage)) {
+		_debug("jumpstart %p {%lx}", backpage, backpage->flags);
+		unlock_page(backpage);
+	}
+
+	/* it'll reappear on the todo list */
+	_leave(" = -EINPROGRESS");
+	return -EINPROGRESS;
+
+unlock_discard:
+	unlock_page(backpage);
+discard:
+	spin_lock_irq(&object->work_lock);
+	list_del(&monitor->op_link);
+	spin_unlock_irq(&object->work_lock);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * copy data from backing pages to netfs pages to complete a read operation
+ * - driven by FS-Cache's thread pool
+ */
+static void cachefiles_read_copier(struct fscache_operation *_op)
+{
+	struct cachefiles_one_read *monitor;
+	struct cachefiles_object *object;
+	struct fscache_retrieval *op;
+	int error, max;
+
+	op = container_of(_op, struct fscache_retrieval, op);
+	object = container_of(op->op.object,
+			      struct cachefiles_object, fscache);
+
+	_enter("{ino=%lu}", d_backing_inode(object->backer)->i_ino);
+
+	max = 8;
+	spin_lock_irq(&object->work_lock);
+
+	while (!list_empty(&op->to_do)) {
+		monitor = list_entry(op->to_do.next,
+				     struct cachefiles_one_read, op_link);
+		list_del(&monitor->op_link);
+
+		spin_unlock_irq(&object->work_lock);
+
+		_debug("- copy {%lu}", monitor->back_page->index);
+
+	recheck:
+		if (test_bit(FSCACHE_COOKIE_INVALIDATING,
+			     &object->fscache.cookie->flags)) {
+			error = -ESTALE;
+		} else if (PageUptodate(monitor->back_page)) {
+			copy_highpage(monitor->netfs_page, monitor->back_page);
+			fscache_mark_page_cached(monitor->op,
+						 monitor->netfs_page);
+			error = 0;
+		} else if (!PageError(monitor->back_page)) {
+			/* the page has probably been truncated */
+			error = cachefiles_read_reissue(object, monitor);
+			if (error == -EINPROGRESS)
+				goto next;
+			goto recheck;
+		} else {
+			cachefiles_io_error_obj(
+				object,
+				"Readpage failed on backing file %lx",
+				(unsigned long) monitor->back_page->flags);
+			error = -EIO;
+		}
+
+		put_page(monitor->back_page);
+
+		fscache_end_io(op, monitor->netfs_page, error);
+		put_page(monitor->netfs_page);
+		fscache_retrieval_complete(op, 1);
+		fscache_put_retrieval(op);
+		kfree(monitor);
+
+	next:
+		/* let the thread pool have some air occasionally */
+		max--;
+		if (max < 0 || need_resched()) {
+			if (!list_empty(&op->to_do))
+				fscache_enqueue_retrieval(op);
+			_leave(" [maxed out]");
+			return;
+		}
+
+		spin_lock_irq(&object->work_lock);
+	}
+
+	spin_unlock_irq(&object->work_lock);
+	_leave("");
+}
+
+/*
+ * read the corresponding page to the given set from the backing file
+ * - an uncertain page is simply discarded, to be tried again another time
+ */
+static int cachefiles_read_backing_file_one(struct cachefiles_object *object,
+					    struct fscache_retrieval *op,
+					    struct page *netpage)
+{
+	struct cachefiles_one_read *monitor;
+	struct address_space *bmapping;
+	struct page *newpage, *backpage;
+	int ret;
+
+	_enter("");
+
+	_debug("read back %p{%lu,%d}",
+	       netpage, netpage->index, page_count(netpage));
+
+	monitor = kzalloc(sizeof(*monitor), cachefiles_gfp);
+	if (!monitor)
+		goto nomem;
+
+	monitor->netfs_page = netpage;
+	monitor->op = fscache_get_retrieval(op);
+
+	init_waitqueue_func_entry(&monitor->monitor, cachefiles_read_waiter);
+
+	/* attempt to get hold of the backing page */
+	bmapping = d_backing_inode(object->backer)->i_mapping;
+	newpage = NULL;
+
+	for (;;) {
+		backpage = find_get_page(bmapping, netpage->index);
+		if (backpage)
+			goto backing_page_already_present;
+
+		if (!newpage) {
+			newpage = __page_cache_alloc(cachefiles_gfp);
+			if (!newpage)
+				goto nomem_monitor;
+		}
+
+		ret = add_to_page_cache_lru(newpage, bmapping,
+					    netpage->index, cachefiles_gfp);
+		if (ret == 0)
+			goto installed_new_backing_page;
+		if (ret != -EEXIST)
+			goto nomem_page;
+	}
+
+	/* we've installed a new backing page, so now we need to start
+	 * it reading */
+installed_new_backing_page:
+	_debug("- new %p", newpage);
+
+	backpage = newpage;
+	newpage = NULL;
+
+read_backing_page:
+	ret = bmapping->a_ops->readpage(NULL, backpage);
+	if (ret < 0)
+		goto read_error;
+
+	/* set the monitor to transfer the data across */
+monitor_backing_page:
+	_debug("- monitor add");
+
+	/* install the monitor */
+	get_page(monitor->netfs_page);
+	get_page(backpage);
+	monitor->back_page = backpage;
+	monitor->monitor.private = backpage;
+	add_page_wait_queue(backpage, &monitor->monitor);
+	monitor = NULL;
+
+	/* but the page may have been read before the monitor was installed, so
+	 * the monitor may miss the event - so we have to ensure that we do get
+	 * one in such a case */
+	if (trylock_page(backpage)) {
+		_debug("jumpstart %p {%lx}", backpage, backpage->flags);
+		unlock_page(backpage);
+	}
+	goto success;
+
+	/* if the backing page is already present, it can be in one of
+	 * three states: read in progress, read failed or read okay */
+backing_page_already_present:
+	_debug("- present");
+
+	if (newpage) {
+		put_page(newpage);
+		newpage = NULL;
+	}
+
+	if (PageError(backpage))
+		goto io_error;
+
+	if (PageUptodate(backpage))
+		goto backing_page_already_uptodate;
+
+	if (!trylock_page(backpage))
+		goto monitor_backing_page;
+	_debug("read %p {%lx}", backpage, backpage->flags);
+	goto read_backing_page;
+
+	/* the backing page is already up to date, attach the netfs
+	 * page to the pagecache and LRU and copy the data across */
+backing_page_already_uptodate:
+	_debug("- uptodate");
+
+	fscache_mark_page_cached(op, netpage);
+
+	copy_highpage(netpage, backpage);
+	fscache_end_io(op, netpage, 0);
+	fscache_retrieval_complete(op, 1);
+
+success:
+	_debug("success");
+	ret = 0;
+
+out:
+	if (backpage)
+		put_page(backpage);
+	if (monitor) {
+		fscache_put_retrieval(monitor->op);
+		kfree(monitor);
+	}
+	_leave(" = %d", ret);
+	return ret;
+
+read_error:
+	_debug("read error %d", ret);
+	if (ret == -ENOMEM) {
+		fscache_retrieval_complete(op, 1);
+		goto out;
+	}
+io_error:
+	cachefiles_io_error_obj(object, "Page read error on backing file");
+	fscache_retrieval_complete(op, 1);
+	ret = -ENOBUFS;
+	goto out;
+
+nomem_page:
+	put_page(newpage);
+nomem_monitor:
+	fscache_put_retrieval(monitor->op);
+	kfree(monitor);
+nomem:
+	fscache_retrieval_complete(op, 1);
+	_leave(" = -ENOMEM");
+	return -ENOMEM;
+}
+
+/*
+ * read a page from the cache or allocate a block in which to store it
+ * - cache withdrawal is prevented by the caller
+ * - returns -EINTR if interrupted
+ * - returns -ENOMEM if ran out of memory
+ * - returns -ENOBUFS if no buffers can be made available
+ * - returns -ENOBUFS if page is beyond EOF
+ * - if the page is backed by a block in the cache:
+ *   - a read will be started which will call the callback on completion
+ *   - 0 will be returned
+ * - else if the page is unbacked:
+ *   - the metadata will be retained
+ *   - -ENODATA will be returned
+ */
+int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
+				  struct page *page,
+				  gfp_t gfp)
+{
+	struct cachefiles_object *object;
+	struct cachefiles_cache *cache;
+	struct inode *inode;
+	sector_t block;
+	unsigned shift;
+	int ret, ret2;
+
+	object = container_of(op->op.object,
+			      struct cachefiles_object, fscache);
+	cache = container_of(object->fscache.cache,
+			     struct cachefiles_cache, cache);
+
+	_enter("{%p},{%lx},,,", object, page->index);
+
+	if (!object->backer)
+		goto enobufs;
+
+	inode = d_backing_inode(object->backer);
+	ASSERT(S_ISREG(inode->i_mode));
+
+	/* calculate the shift required to use bmap */
+	shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
+
+	op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
+	op->op.flags |= FSCACHE_OP_ASYNC;
+	op->op.processor = cachefiles_read_copier;
+
+	/* we assume the absence or presence of the first block is a good
+	 * enough indication for the page as a whole
+	 * - TODO: don't use bmap() for this as it is _not_ actually good
+	 *   enough for this as it doesn't indicate errors, but it's all we've
+	 *   got for the moment
+	 */
+	block = page->index;
+	block <<= shift;
+
+	ret2 = bmap(inode, &block);
+	ASSERT(ret2 == 0);
+
+	_debug("%llx -> %llx",
+	       (unsigned long long) (page->index << shift),
+	       (unsigned long long) block);
+
+	if (block) {
+		/* submit the apparently valid page to the backing fs to be
+		 * read from disk */
+		ret = cachefiles_read_backing_file_one(object, op, page);
+	} else if (cachefiles_has_space(cache, 0, 1) == 0) {
+		/* there's space in the cache we can use */
+		fscache_mark_page_cached(op, page);
+		fscache_retrieval_complete(op, 1);
+		ret = -ENODATA;
+	} else {
+		goto enobufs;
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+
+enobufs:
+	fscache_retrieval_complete(op, 1);
+	_leave(" = -ENOBUFS");
+	return -ENOBUFS;
+}
+
+/*
+ * read the corresponding pages to the given set from the backing file
+ * - any uncertain pages are simply discarded, to be tried again another time
+ */
+static int cachefiles_read_backing_file(struct cachefiles_object *object,
+					struct fscache_retrieval *op,
+					struct list_head *list)
+{
+	struct cachefiles_one_read *monitor = NULL;
+	struct address_space *bmapping = d_backing_inode(object->backer)->i_mapping;
+	struct page *newpage = NULL, *netpage, *_n, *backpage = NULL;
+	int ret = 0;
+
+	_enter("");
+
+	list_for_each_entry_safe(netpage, _n, list, lru) {
+		list_del(&netpage->lru);
+
+		_debug("read back %p{%lu,%d}",
+		       netpage, netpage->index, page_count(netpage));
+
+		if (!monitor) {
+			monitor = kzalloc(sizeof(*monitor), cachefiles_gfp);
+			if (!monitor)
+				goto nomem;
+
+			monitor->op = fscache_get_retrieval(op);
+			init_waitqueue_func_entry(&monitor->monitor,
+						  cachefiles_read_waiter);
+		}
+
+		for (;;) {
+			backpage = find_get_page(bmapping, netpage->index);
+			if (backpage)
+				goto backing_page_already_present;
+
+			if (!newpage) {
+				newpage = __page_cache_alloc(cachefiles_gfp);
+				if (!newpage)
+					goto nomem;
+			}
+
+			ret = add_to_page_cache_lru(newpage, bmapping,
+						    netpage->index,
+						    cachefiles_gfp);
+			if (ret == 0)
+				goto installed_new_backing_page;
+			if (ret != -EEXIST)
+				goto nomem;
+		}
+
+		/* we've installed a new backing page, so now we need
+		 * to start it reading */
+	installed_new_backing_page:
+		_debug("- new %p", newpage);
+
+		backpage = newpage;
+		newpage = NULL;
+
+	reread_backing_page:
+		ret = bmapping->a_ops->readpage(NULL, backpage);
+		if (ret < 0)
+			goto read_error;
+
+		/* add the netfs page to the pagecache and LRU, and set the
+		 * monitor to transfer the data across */
+	monitor_backing_page:
+		_debug("- monitor add");
+
+		ret = add_to_page_cache_lru(netpage, op->mapping,
+					    netpage->index, cachefiles_gfp);
+		if (ret < 0) {
+			if (ret == -EEXIST) {
+				put_page(backpage);
+				backpage = NULL;
+				put_page(netpage);
+				netpage = NULL;
+				fscache_retrieval_complete(op, 1);
+				continue;
+			}
+			goto nomem;
+		}
+
+		/* install a monitor */
+		get_page(netpage);
+		monitor->netfs_page = netpage;
+
+		get_page(backpage);
+		monitor->back_page = backpage;
+		monitor->monitor.private = backpage;
+		add_page_wait_queue(backpage, &monitor->monitor);
+		monitor = NULL;
+
+		/* but the page may have been read before the monitor was
+		 * installed, so the monitor may miss the event - so we have to
+		 * ensure that we do get one in such a case */
+		if (trylock_page(backpage)) {
+			_debug("2unlock %p {%lx}", backpage, backpage->flags);
+			unlock_page(backpage);
+		}
+
+		put_page(backpage);
+		backpage = NULL;
+
+		put_page(netpage);
+		netpage = NULL;
+		continue;
+
+		/* if the backing page is already present, it can be in one of
+		 * three states: read in progress, read failed or read okay */
+	backing_page_already_present:
+		_debug("- present %p", backpage);
+
+		if (PageError(backpage))
+			goto io_error;
+
+		if (PageUptodate(backpage))
+			goto backing_page_already_uptodate;
+
+		_debug("- not ready %p{%lx}", backpage, backpage->flags);
+
+		if (!trylock_page(backpage))
+			goto monitor_backing_page;
+
+		if (PageError(backpage)) {
+			_debug("error %lx", backpage->flags);
+			unlock_page(backpage);
+			goto io_error;
+		}
+
+		if (PageUptodate(backpage))
+			goto backing_page_already_uptodate_unlock;
+
+		/* we've locked a page that's neither up to date nor erroneous,
+		 * so we need to attempt to read it again */
+		goto reread_backing_page;
+
+		/* the backing page is already up to date, attach the netfs
+		 * page to the pagecache and LRU and copy the data across */
+	backing_page_already_uptodate_unlock:
+		_debug("uptodate %lx", backpage->flags);
+		unlock_page(backpage);
+	backing_page_already_uptodate:
+		_debug("- uptodate");
+
+		ret = add_to_page_cache_lru(netpage, op->mapping,
+					    netpage->index, cachefiles_gfp);
+		if (ret < 0) {
+			if (ret == -EEXIST) {
+				put_page(backpage);
+				backpage = NULL;
+				put_page(netpage);
+				netpage = NULL;
+				fscache_retrieval_complete(op, 1);
+				continue;
+			}
+			goto nomem;
+		}
+
+		copy_highpage(netpage, backpage);
+
+		put_page(backpage);
+		backpage = NULL;
+
+		fscache_mark_page_cached(op, netpage);
+
+		/* the netpage is unlocked and marked up to date here */
+		fscache_end_io(op, netpage, 0);
+		put_page(netpage);
+		netpage = NULL;
+		fscache_retrieval_complete(op, 1);
+		continue;
+	}
+
+	netpage = NULL;
+
+	_debug("out");
+
+out:
+	/* tidy up */
+	if (newpage)
+		put_page(newpage);
+	if (netpage)
+		put_page(netpage);
+	if (backpage)
+		put_page(backpage);
+	if (monitor) {
+		fscache_put_retrieval(op);
+		kfree(monitor);
+	}
+
+	list_for_each_entry_safe(netpage, _n, list, lru) {
+		list_del(&netpage->lru);
+		put_page(netpage);
+		fscache_retrieval_complete(op, 1);
+	}
+
+	_leave(" = %d", ret);
+	return ret;
+
+nomem:
+	_debug("nomem");
+	ret = -ENOMEM;
+	goto record_page_complete;
+
+read_error:
+	_debug("read error %d", ret);
+	if (ret == -ENOMEM)
+		goto record_page_complete;
+io_error:
+	cachefiles_io_error_obj(object, "Page read error on backing file");
+	ret = -ENOBUFS;
+record_page_complete:
+	fscache_retrieval_complete(op, 1);
+	goto out;
+}
+
+/*
+ * read a list of pages from the cache or allocate blocks in which to store
+ * them
+ */
+int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
+				   struct list_head *pages,
+				   unsigned *nr_pages,
+				   gfp_t gfp)
+{
+	struct cachefiles_object *object;
+	struct cachefiles_cache *cache;
+	struct list_head backpages;
+	struct pagevec pagevec;
+	struct inode *inode;
+	struct page *page, *_n;
+	unsigned shift, nrbackpages;
+	int ret, ret2, space;
+
+	object = container_of(op->op.object,
+			      struct cachefiles_object, fscache);
+	cache = container_of(object->fscache.cache,
+			     struct cachefiles_cache, cache);
+
+	_enter("{OBJ%x,%d},,%d,,",
+	       object->fscache.debug_id, atomic_read(&op->op.usage),
+	       *nr_pages);
+
+	if (!object->backer)
+		goto all_enobufs;
+
+	space = 1;
+	if (cachefiles_has_space(cache, 0, *nr_pages) < 0)
+		space = 0;
+
+	inode = d_backing_inode(object->backer);
+	ASSERT(S_ISREG(inode->i_mode));
+
+	/* calculate the shift required to use bmap */
+	shift = PAGE_SHIFT - inode->i_sb->s_blocksize_bits;
+
+	pagevec_init(&pagevec);
+
+	op->op.flags &= FSCACHE_OP_KEEP_FLAGS;
+	op->op.flags |= FSCACHE_OP_ASYNC;
+	op->op.processor = cachefiles_read_copier;
+
+	INIT_LIST_HEAD(&backpages);
+	nrbackpages = 0;
+
+	ret = space ? -ENODATA : -ENOBUFS;
+	list_for_each_entry_safe(page, _n, pages, lru) {
+		sector_t block;
+
+		/* we assume the absence or presence of the first block is a
+		 * good enough indication for the page as a whole
+		 * - TODO: don't use bmap() for this as it is _not_ actually
+		 *   good enough for this as it doesn't indicate errors, but
+		 *   it's all we've got for the moment
+		 */
+		block = page->index;
+		block <<= shift;
+
+		ret2 = bmap(inode, &block);
+		ASSERT(ret2 == 0);
+
+		_debug("%llx -> %llx",
+		       (unsigned long long) (page->index << shift),
+		       (unsigned long long) block);
+
+		if (block) {
+			/* we have data - add it to the list to give to the
+			 * backing fs */
+			list_move(&page->lru, &backpages);
+			(*nr_pages)--;
+			nrbackpages++;
+		} else if (space && pagevec_add(&pagevec, page) == 0) {
+			fscache_mark_pages_cached(op, &pagevec);
+			fscache_retrieval_complete(op, 1);
+			ret = -ENODATA;
+		} else {
+			fscache_retrieval_complete(op, 1);
+		}
+	}
+
+	if (pagevec_count(&pagevec) > 0)
+		fscache_mark_pages_cached(op, &pagevec);
+
+	if (list_empty(pages))
+		ret = 0;
+
+	/* submit the apparently valid pages to the backing fs to be read from
+	 * disk */
+	if (nrbackpages > 0) {
+		ret2 = cachefiles_read_backing_file(object, op, &backpages);
+		if (ret2 == -ENOMEM || ret2 == -EINTR)
+			ret = ret2;
+	}
+
+	_leave(" = %d [nr=%u%s]",
+	       ret, *nr_pages, list_empty(pages) ? " empty" : "");
+	return ret;
+
+all_enobufs:
+	fscache_retrieval_complete(op, *nr_pages);
+	return -ENOBUFS;
+}
+
+/*
+ * allocate a block in the cache in which to store a page
+ * - cache withdrawal is prevented by the caller
+ * - returns -EINTR if interrupted
+ * - returns -ENOMEM if ran out of memory
+ * - returns -ENOBUFS if no buffers can be made available
+ * - returns -ENOBUFS if page is beyond EOF
+ * - otherwise:
+ *   - the metadata will be retained
+ *   - 0 will be returned
+ */
+int cachefiles_allocate_page(struct fscache_retrieval *op,
+			     struct page *page,
+			     gfp_t gfp)
+{
+	struct cachefiles_object *object;
+	struct cachefiles_cache *cache;
+	int ret;
+
+	object = container_of(op->op.object,
+			      struct cachefiles_object, fscache);
+	cache = container_of(object->fscache.cache,
+			     struct cachefiles_cache, cache);
+
+	_enter("%p,{%lx},", object, page->index);
+
+	ret = cachefiles_has_space(cache, 0, 1);
+	if (ret == 0)
+		fscache_mark_page_cached(op, page);
+	else
+		ret = -ENOBUFS;
+
+	fscache_retrieval_complete(op, 1);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * allocate blocks in the cache in which to store a set of pages
+ * - cache withdrawal is prevented by the caller
+ * - returns -EINTR if interrupted
+ * - returns -ENOMEM if ran out of memory
+ * - returns -ENOBUFS if some buffers couldn't be made available
+ * - returns -ENOBUFS if some pages are beyond EOF
+ * - otherwise:
+ *   - -ENODATA will be returned
+ * - metadata will be retained for any page marked
+ */
+int cachefiles_allocate_pages(struct fscache_retrieval *op,
+			      struct list_head *pages,
+			      unsigned *nr_pages,
+			      gfp_t gfp)
+{
+	struct cachefiles_object *object;
+	struct cachefiles_cache *cache;
+	struct pagevec pagevec;
+	struct page *page;
+	int ret;
+
+	object = container_of(op->op.object,
+			      struct cachefiles_object, fscache);
+	cache = container_of(object->fscache.cache,
+			     struct cachefiles_cache, cache);
+
+	_enter("%p,,,%d,", object, *nr_pages);
+
+	ret = cachefiles_has_space(cache, 0, *nr_pages);
+	if (ret == 0) {
+		pagevec_init(&pagevec);
+
+		list_for_each_entry(page, pages, lru) {
+			if (pagevec_add(&pagevec, page) == 0)
+				fscache_mark_pages_cached(op, &pagevec);
+		}
+
+		if (pagevec_count(&pagevec) > 0)
+			fscache_mark_pages_cached(op, &pagevec);
+		ret = -ENODATA;
+	} else {
+		ret = -ENOBUFS;
+	}
+
+	fscache_retrieval_complete(op, *nr_pages);
+	_leave(" = %d", ret);
+	return ret;
+}
+
+/*
+ * request a page be stored in the cache
+ * - cache withdrawal is prevented by the caller
+ * - this request may be ignored if there's no cache block available, in which
+ *   case -ENOBUFS will be returned
+ * - if the op is in progress, 0 will be returned
+ */
+int cachefiles_write_page(struct fscache_storage *op, struct page *page)
+{
+	struct cachefiles_object *object;
+	struct cachefiles_cache *cache;
+	struct file *file;
+	struct path path;
+	loff_t pos, eof;
+	size_t len;
+	void *data;
+	int ret = -ENOBUFS;
+
+	ASSERT(op != NULL);
+	ASSERT(page != NULL);
+
+	object = container_of(op->op.object,
+			      struct cachefiles_object, fscache);
+
+	_enter("%p,%p{%lx},,,", object, page, page->index);
+
+	if (!object->backer) {
+		_leave(" = -ENOBUFS");
+		return -ENOBUFS;
+	}
+
+	ASSERT(d_is_reg(object->backer));
+
+	cache = container_of(object->fscache.cache,
+			     struct cachefiles_cache, cache);
+
+	pos = (loff_t)page->index << PAGE_SHIFT;
+
+	/* We mustn't write more data than we have, so we have to beware of a
+	 * partial page at EOF.
+	 */
+	eof = object->fscache.store_limit_l;
+	if (pos >= eof)
+		goto error;
+
+	/* write the page to the backing filesystem and let it store it in its
+	 * own time */
+	path.mnt = cache->mnt;
+	path.dentry = object->backer;
+	file = dentry_open(&path, O_RDWR | O_LARGEFILE, cache->cache_cred);
+	if (IS_ERR(file)) {
+		ret = PTR_ERR(file);
+		goto error_2;
+	}
+
+	len = PAGE_SIZE;
+	if (eof & ~PAGE_MASK) {
+		if (eof - pos < PAGE_SIZE) {
+			_debug("cut short %llx to %llx",
+			       pos, eof);
+			len = eof - pos;
+			ASSERTCMP(pos + len, ==, eof);
+		}
+	}
+
+	data = kmap(page);
+	ret = kernel_write(file, data, len, &pos);
+	kunmap(page);
+	fput(file);
+	if (ret != len)
+		goto error_eio;
+
+	_leave(" = 0");
+	return 0;
+
+error_eio:
+	ret = -EIO;
+error_2:
+	if (ret == -EIO)
+		cachefiles_io_error_obj(object,
+					"Write page to backing file failed");
+error:
+	_leave(" = -ENOBUFS [%d]", ret);
+	return -ENOBUFS;
+}
+
+/*
+ * detach a backing block from a page
+ * - cache withdrawal is prevented by the caller
+ */
+void cachefiles_uncache_page(struct fscache_object *_object, struct page *page)
+	__releases(&object->fscache.cookie->lock)
+{
+	struct cachefiles_object *object;
+
+	object = container_of(_object, struct cachefiles_object, fscache);
+
+	_enter("%p,{%lu}", object, page->index);
+
+	spin_unlock(&object->fscache.cookie->lock);
+}