netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 169 insertions, 0 deletions

diff --git a/drivers/md/persistent-data/dm-space-map.h b/drivers/md/persistent-data/dm-space-map.h
new file mode 100644
index 000000000..6bf69922b
--- /dev/null
+++ b/drivers/md/persistent-data/dm-space-map.h
@@ -0,0 +1,169 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef _LINUX_DM_SPACE_MAP_H
+#define _LINUX_DM_SPACE_MAP_H
+
+#include "dm-block-manager.h"
+
+typedef void (*dm_sm_threshold_fn)(void *context);
+
+/*
+ * struct dm_space_map keeps a record of how many times each block in a device
+ * is referenced.  It needs to be fixed on disk as part of the transaction.
+ */
+struct dm_space_map {
+	void (*destroy)(struct dm_space_map *sm);
+
+	/*
+	 * You must commit before allocating the newly added space.
+	 */
+	int (*extend)(struct dm_space_map *sm, dm_block_t extra_blocks);
+
+	/*
+	 * Extensions do not appear in this count until after commit has
+	 * been called.
+	 */
+	int (*get_nr_blocks)(struct dm_space_map *sm, dm_block_t *count);
+
+	/*
+	 * Space maps must never allocate a block from the previous
+	 * transaction, in case we need to rollback.  This complicates the
+	 * semantics of get_nr_free(), it should return the number of blocks
+	 * that are available for allocation _now_.  For instance you may
+	 * have blocks with a zero reference count that will not be
+	 * available for allocation until after the next commit.
+	 */
+	int (*get_nr_free)(struct dm_space_map *sm, dm_block_t *count);
+
+	int (*get_count)(struct dm_space_map *sm, dm_block_t b, uint32_t *result);
+	int (*count_is_more_than_one)(struct dm_space_map *sm, dm_block_t b,
+				      int *result);
+	int (*set_count)(struct dm_space_map *sm, dm_block_t b, uint32_t count);
+
+	int (*commit)(struct dm_space_map *sm);
+
+	int (*inc_blocks)(struct dm_space_map *sm, dm_block_t b, dm_block_t e);
+	int (*dec_blocks)(struct dm_space_map *sm, dm_block_t b, dm_block_t e);
+
+	/*
+	 * new_block will increment the returned block.
+	 */
+	int (*new_block)(struct dm_space_map *sm, dm_block_t *b);
+
+	/*
+	 * The root contains all the information needed to fix the space map.
+	 * Generally this info is small, so squirrel it away in a disk block
+	 * along with other info.
+	 */
+	int (*root_size)(struct dm_space_map *sm, size_t *result);
+	int (*copy_root)(struct dm_space_map *sm, void *copy_to_here_le, size_t len);
+
+	/*
+	 * You can register one threshold callback which is edge-triggered
+	 * when the free space in the space map drops below the threshold.
+	 */
+	int (*register_threshold_callback)(struct dm_space_map *sm,
+					   dm_block_t threshold,
+					   dm_sm_threshold_fn fn,
+					   void *context);
+};
+
+/*----------------------------------------------------------------*/
+
+static inline void dm_sm_destroy(struct dm_space_map *sm)
+{
+	if (sm)
+		sm->destroy(sm);
+}
+
+static inline int dm_sm_extend(struct dm_space_map *sm, dm_block_t extra_blocks)
+{
+	return sm->extend(sm, extra_blocks);
+}
+
+static inline int dm_sm_get_nr_blocks(struct dm_space_map *sm, dm_block_t *count)
+{
+	return sm->get_nr_blocks(sm, count);
+}
+
+static inline int dm_sm_get_nr_free(struct dm_space_map *sm, dm_block_t *count)
+{
+	return sm->get_nr_free(sm, count);
+}
+
+static inline int dm_sm_get_count(struct dm_space_map *sm, dm_block_t b,
+				  uint32_t *result)
+{
+	return sm->get_count(sm, b, result);
+}
+
+static inline int dm_sm_count_is_more_than_one(struct dm_space_map *sm,
+					       dm_block_t b, int *result)
+{
+	return sm->count_is_more_than_one(sm, b, result);
+}
+
+static inline int dm_sm_set_count(struct dm_space_map *sm, dm_block_t b,
+				  uint32_t count)
+{
+	return sm->set_count(sm, b, count);
+}
+
+static inline int dm_sm_commit(struct dm_space_map *sm)
+{
+	return sm->commit(sm);
+}
+
+static inline int dm_sm_inc_blocks(struct dm_space_map *sm, dm_block_t b, dm_block_t e)
+{
+	return sm->inc_blocks(sm, b, e);
+}
+
+static inline int dm_sm_inc_block(struct dm_space_map *sm, dm_block_t b)
+{
+	return dm_sm_inc_blocks(sm, b, b + 1);
+}
+
+static inline int dm_sm_dec_blocks(struct dm_space_map *sm, dm_block_t b, dm_block_t e)
+{
+	return sm->dec_blocks(sm, b, e);
+}
+
+static inline int dm_sm_dec_block(struct dm_space_map *sm, dm_block_t b)
+{
+	return dm_sm_dec_blocks(sm, b, b + 1);
+}
+
+static inline int dm_sm_new_block(struct dm_space_map *sm, dm_block_t *b)
+{
+	return sm->new_block(sm, b);
+}
+
+static inline int dm_sm_root_size(struct dm_space_map *sm, size_t *result)
+{
+	return sm->root_size(sm, result);
+}
+
+static inline int dm_sm_copy_root(struct dm_space_map *sm, void *copy_to_here_le, size_t len)
+{
+	return sm->copy_root(sm, copy_to_here_le, len);
+}
+
+static inline int dm_sm_register_threshold_callback(struct dm_space_map *sm,
+						    dm_block_t threshold,
+						    dm_sm_threshold_fn fn,
+						    void *context)
+{
+	if (sm->register_threshold_callback)
+		return sm->register_threshold_callback(sm, threshold, fn, context);
+
+	return -EINVAL;
+}
+
+
+#endif	/* _LINUX_DM_SPACE_MAP_H */