1/* SPDX-License-Identifier: GPL-2.0-or-later */
  2/* Network filesystem support services.
  3 *
  4 * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
  5 * Written by David Howells (dhowells@redhat.com)
  6 *
  7 * See:
  8 *
  9 *	Documentation/filesystems/netfs_library.rst
 10 *
 11 * for a description of the network filesystem interface declared here.
 12 */
 13
 14#ifndef _LINUX_NETFS_H
 15#define _LINUX_NETFS_H
 16
 17#include <linux/workqueue.h>
 18#include <linux/fs.h>
 19#include <linux/pagemap.h>
 20
 21/*
 22 * Overload PG_private_2 to give us PG_fscache - this is used to indicate that
 23 * a page is currently backed by a local disk cache
 24 */
 25#define PageFsCache(page)		PagePrivate2((page))
 26#define SetPageFsCache(page)		SetPagePrivate2((page))
 27#define ClearPageFsCache(page)		ClearPagePrivate2((page))
 28#define TestSetPageFsCache(page)	TestSetPagePrivate2((page))
 29#define TestClearPageFsCache(page)	TestClearPagePrivate2((page))
 30
 31/**
 32 * set_page_fscache - Set PG_fscache on a page and take a ref
 33 * @page: The page.
 34 *
 35 * Set the PG_fscache (PG_private_2) flag on a page and take the reference
 36 * needed for the VM to handle its lifetime correctly.  This sets the flag and
 37 * takes the reference unconditionally, so care must be taken not to set the
 38 * flag again if it's already set.
 39 */
 40static inline void set_page_fscache(struct page *page)
 41{
 42	set_page_private_2(page);
 43}
 44
 45/**
 46 * end_page_fscache - Clear PG_fscache and release any waiters
 47 * @page: The page
 48 *
 49 * Clear the PG_fscache (PG_private_2) bit on a page and wake up any sleepers
 50 * waiting for this.  The page ref held for PG_private_2 being set is released.
 51 *
 52 * This is, for example, used when a netfs page is being written to a local
 53 * disk cache, thereby allowing writes to the cache for the same page to be
 54 * serialised.
 55 */
 56static inline void end_page_fscache(struct page *page)
 57{
 58	end_page_private_2(page);
 59}
 60
 61/**
 62 * wait_on_page_fscache - Wait for PG_fscache to be cleared on a page
 63 * @page: The page to wait on
 64 *
 65 * Wait for PG_fscache (aka PG_private_2) to be cleared on a page.
 66 */
 67static inline void wait_on_page_fscache(struct page *page)
 68{
 69	wait_on_page_private_2(page);
 70}
 71
 72/**
 73 * wait_on_page_fscache_killable - Wait for PG_fscache to be cleared on a page
 74 * @page: The page to wait on
 75 *
 76 * Wait for PG_fscache (aka PG_private_2) to be cleared on a page or until a
 77 * fatal signal is received by the calling task.
 78 *
 79 * Return:
 80 * - 0 if successful.
 81 * - -EINTR if a fatal signal was encountered.
 82 */
 83static inline int wait_on_page_fscache_killable(struct page *page)
 84{
 85	return wait_on_page_private_2_killable(page);
 86}
 87
 88enum netfs_read_source {
 89	NETFS_FILL_WITH_ZEROES,
 90	NETFS_DOWNLOAD_FROM_SERVER,
 91	NETFS_READ_FROM_CACHE,
 92	NETFS_INVALID_READ,
 93} __mode(byte);
 94
 95typedef void (*netfs_io_terminated_t)(void *priv, ssize_t transferred_or_error,
 96				      bool was_async);
 97
 98/*
 99 * Resources required to do operations on a cache.
100 */
101struct netfs_cache_resources {
102	const struct netfs_cache_ops	*ops;
103	void				*cache_priv;
104	void				*cache_priv2;
105};
106
107/*
108 * Descriptor for a single component subrequest.
109 */
110struct netfs_read_subrequest {
111	struct netfs_read_request *rreq;	/* Supervising read request */
112	struct list_head	rreq_link;	/* Link in rreq->subrequests */
113	loff_t			start;		/* Where to start the I/O */
114	size_t			len;		/* Size of the I/O */
115	size_t			transferred;	/* Amount of data transferred */
116	refcount_t		usage;
117	short			error;		/* 0 or error that occurred */
118	unsigned short		debug_index;	/* Index in list (for debugging output) */
119	enum netfs_read_source	source;		/* Where to read from */
120	unsigned long		flags;
121#define NETFS_SREQ_WRITE_TO_CACHE	0	/* Set if should write to cache */
122#define NETFS_SREQ_CLEAR_TAIL		1	/* Set if the rest of the read should be cleared */
123#define NETFS_SREQ_SHORT_READ		2	/* Set if there was a short read from the cache */
124#define NETFS_SREQ_SEEK_DATA_READ	3	/* Set if ->read() should SEEK_DATA first */
125#define NETFS_SREQ_NO_PROGRESS		4	/* Set if we didn't manage to read any data */
126};
127
128/*
129 * Descriptor for a read helper request.  This is used to make multiple I/O
130 * requests on a variety of sources and then stitch the result together.
131 */
132struct netfs_read_request {
133	struct work_struct	work;
134	struct inode		*inode;		/* The file being accessed */
135	struct address_space	*mapping;	/* The mapping being accessed */
136	struct netfs_cache_resources cache_resources;
137	struct list_head	subrequests;	/* Requests to fetch I/O from disk or net */
138	void			*netfs_priv;	/* Private data for the netfs */
139	unsigned int		debug_id;
140	unsigned int		cookie_debug_id;
141	atomic_t		nr_rd_ops;	/* Number of read ops in progress */
142	atomic_t		nr_wr_ops;	/* Number of write ops in progress */
143	size_t			submitted;	/* Amount submitted for I/O so far */
144	size_t			len;		/* Length of the request */
145	short			error;		/* 0 or error that occurred */
146	loff_t			i_size;		/* Size of the file */
147	loff_t			start;		/* Start position */
148	pgoff_t			no_unlock_page;	/* Don't unlock this page after read */
149	refcount_t		usage;
150	unsigned long		flags;
151#define NETFS_RREQ_INCOMPLETE_IO	0	/* Some ioreqs terminated short or with error */
152#define NETFS_RREQ_WRITE_TO_CACHE	1	/* Need to write to the cache */
153#define NETFS_RREQ_NO_UNLOCK_PAGE	2	/* Don't unlock no_unlock_page on completion */
154#define NETFS_RREQ_DONT_UNLOCK_PAGES	3	/* Don't unlock the pages on completion */
155#define NETFS_RREQ_FAILED		4	/* The request failed */
156#define NETFS_RREQ_IN_PROGRESS		5	/* Unlocked when the request completes */
157	const struct netfs_read_request_ops *netfs_ops;
158};
159
160/*
161 * Operations the network filesystem can/must provide to the helpers.
162 */
163struct netfs_read_request_ops {
164	bool (*is_cache_enabled)(struct inode *inode);
165	void (*init_rreq)(struct netfs_read_request *rreq, struct file *file);
166	int (*begin_cache_operation)(struct netfs_read_request *rreq);
167	void (*expand_readahead)(struct netfs_read_request *rreq);
168	bool (*clamp_length)(struct netfs_read_subrequest *subreq);
169	void (*issue_op)(struct netfs_read_subrequest *subreq);
170	bool (*is_still_valid)(struct netfs_read_request *rreq);
171	int (*check_write_begin)(struct file *file, loff_t pos, unsigned len,
172				 struct page *page, void **_fsdata);
173	void (*done)(struct netfs_read_request *rreq);
174	void (*cleanup)(struct address_space *mapping, void *netfs_priv);
175};
176
177/*
178 * Table of operations for access to a cache.  This is obtained by
179 * rreq->ops->begin_cache_operation().
180 */
181struct netfs_cache_ops {
182	/* End an operation */
183	void (*end_operation)(struct netfs_cache_resources *cres);
184
185	/* Read data from the cache */
186	int (*read)(struct netfs_cache_resources *cres,
187		    loff_t start_pos,
188		    struct iov_iter *iter,
189		    bool seek_data,
190		    netfs_io_terminated_t term_func,
191		    void *term_func_priv);
192
193	/* Write data to the cache */
194	int (*write)(struct netfs_cache_resources *cres,
195		     loff_t start_pos,
196		     struct iov_iter *iter,
197		     netfs_io_terminated_t term_func,
198		     void *term_func_priv);
199
200	/* Expand readahead request */
201	void (*expand_readahead)(struct netfs_cache_resources *cres,
202				 loff_t *_start, size_t *_len, loff_t i_size);
203
204	/* Prepare a read operation, shortening it to a cached/uncached
205	 * boundary as appropriate.
206	 */
207	enum netfs_read_source (*prepare_read)(struct netfs_read_subrequest *subreq,
208					       loff_t i_size);
209
210	/* Prepare a write operation, working out what part of the write we can
211	 * actually do.
212	 */
213	int (*prepare_write)(struct netfs_cache_resources *cres,
214			     loff_t *_start, size_t *_len, loff_t i_size);
215};
216
217struct readahead_control;
218extern void netfs_readahead(struct readahead_control *,
219			    const struct netfs_read_request_ops *,
220			    void *);
221extern int netfs_readpage(struct file *,
222			  struct page *,
223			  const struct netfs_read_request_ops *,
224			  void *);
225extern int netfs_write_begin(struct file *, struct address_space *,
226			     loff_t, unsigned int, unsigned int, struct page **,
227			     void **,
228			     const struct netfs_read_request_ops *,
229			     void *);
230
231extern void netfs_subreq_terminated(struct netfs_read_subrequest *, ssize_t, bool);
232extern void netfs_stats_show(struct seq_file *);
233
234#endif /* _LINUX_NETFS_H */