1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * linux/include/linux/relay.h
4 *
5 * Copyright (C) 2002, 2003 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
6 * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour (karim@opersys.com)
7 *
8 * CONFIG_RELAY definitions and declarations
9 */
10
11#ifndef _LINUX_RELAY_H
12#define _LINUX_RELAY_H
13
14#include <linux/types.h>
15#include <linux/sched.h>
16#include <linux/timer.h>
17#include <linux/wait.h>
18#include <linux/list.h>
19#include <linux/irq_work.h>
20#include <linux/bug.h>
21#include <linux/fs.h>
22#include <linux/poll.h>
23#include <linux/kref.h>
24#include <linux/percpu.h>
25
26/*
27 * Tracks changes to rchan/rchan_buf structs
28 */
29#define RELAYFS_CHANNEL_VERSION		7
30
31/*
32 * Per-cpu relay channel buffer
33 */
34struct rchan_buf
35{
36	void *start;			/* start of channel buffer */
37	void *data;			/* start of current sub-buffer */
38	size_t offset;			/* current offset into sub-buffer */
39	size_t subbufs_produced;	/* count of sub-buffers produced */
40	size_t subbufs_consumed;	/* count of sub-buffers consumed */
41	struct rchan *chan;		/* associated channel */
42	wait_queue_head_t read_wait;	/* reader wait queue */
43	struct irq_work wakeup_work;	/* reader wakeup */
44	struct dentry *dentry;		/* channel file dentry */
45	struct kref kref;		/* channel buffer refcount */
46	struct page **page_array;	/* array of current buffer pages */
47	unsigned int page_count;	/* number of current buffer pages */
48	unsigned int finalized;		/* buffer has been finalized */
49	size_t *padding;		/* padding counts per sub-buffer */
50	size_t prev_padding;		/* temporary variable */
51	size_t bytes_consumed;		/* bytes consumed in cur read subbuf */
52	size_t early_bytes;		/* bytes consumed before VFS inited */
53	unsigned int cpu;		/* this buf's cpu */
54} ____cacheline_aligned;
55
56/*
57 * Relay channel data structure
58 */
59struct rchan
60{
61	u32 version;			/* the version of this struct */
62	size_t subbuf_size;		/* sub-buffer size */
63	size_t n_subbufs;		/* number of sub-buffers per buffer */
64	size_t alloc_size;		/* total buffer size allocated */
65	const struct rchan_callbacks *cb; /* client callbacks */
66	struct kref kref;		/* channel refcount */
67	void *private_data;		/* for user-defined data */
68	size_t last_toobig;		/* tried to log event > subbuf size */
69	struct rchan_buf * __percpu *buf; /* per-cpu channel buffers */
70	int is_global;			/* One global buffer ? */
71	struct list_head list;		/* for channel list */
72	struct dentry *parent;		/* parent dentry passed to open */
73	int has_base_filename;		/* has a filename associated? */
74	char base_filename[NAME_MAX];	/* saved base filename */
75};
76
77/*
78 * Relay channel client callbacks
79 */
80struct rchan_callbacks
81{
82	/*
83	 * subbuf_start - called on buffer-switch to a new sub-buffer
84	 * @buf: the channel buffer containing the new sub-buffer
85	 * @subbuf: the start of the new sub-buffer
86	 * @prev_subbuf: the start of the previous sub-buffer
87	 * @prev_padding: unused space at the end of previous sub-buffer
88	 *
89	 * The client should return 1 to continue logging, 0 to stop
90	 * logging.
91	 *
92	 * This callback is optional.
93	 *
94	 * NOTE: subbuf_start will also be invoked when the buffer is
95	 *       created, so that the first sub-buffer can be initialized
96	 *       if necessary.  In this case, prev_subbuf will be NULL.
97	 *
98	 * NOTE: the client can reserve bytes at the beginning of the new
99	 *       sub-buffer by calling subbuf_start_reserve() in this callback.
100	 */
101	int (*subbuf_start) (struct rchan_buf *buf,
102			     void *subbuf,
103			     void *prev_subbuf,
104			     size_t prev_padding);
105
106	/*
107	 * create_buf_file - create file to represent a relay channel buffer
108	 * @filename: the name of the file to create
109	 * @parent: the parent of the file to create
110	 * @mode: the mode of the file to create
111	 * @buf: the channel buffer
112	 * @is_global: outparam - set non-zero if the buffer should be global
113	 *
114	 * Called during relay_open(), once for each per-cpu buffer,
115	 * to allow the client to create a file to be used to
116	 * represent the corresponding channel buffer.  If the file is
117	 * created outside of relay, the parent must also exist in
118	 * that filesystem.
119	 *
120	 * The callback should return the dentry of the file created
121	 * to represent the relay buffer.
122	 *
123	 * Setting the is_global outparam to a non-zero value will
124	 * cause relay_open() to create a single global buffer rather
125	 * than the default set of per-cpu buffers.
126	 *
127	 * This callback is mandatory.
128	 *
129	 * See Documentation/filesystems/relay.rst for more info.
130	 */
131	struct dentry *(*create_buf_file)(const char *filename,
132					  struct dentry *parent,
133					  umode_t mode,
134					  struct rchan_buf *buf,
135					  int *is_global);
136
137	/*
138	 * remove_buf_file - remove file representing a relay channel buffer
139	 * @dentry: the dentry of the file to remove
140	 *
141	 * Called during relay_close(), once for each per-cpu buffer,
142	 * to allow the client to remove a file used to represent a
143	 * channel buffer.
144	 *
145	 * The callback should return 0 if successful, negative if not.
146	 *
147	 * This callback is mandatory.
148	 */
149	int (*remove_buf_file)(struct dentry *dentry);
150};
151
152/*
153 * CONFIG_RELAY kernel API, kernel/relay.c
154 */
155
156struct rchan *relay_open(const char *base_filename,
157			 struct dentry *parent,
158			 size_t subbuf_size,
159			 size_t n_subbufs,
160			 const struct rchan_callbacks *cb,
161			 void *private_data);
162extern int relay_late_setup_files(struct rchan *chan,
163				  const char *base_filename,
164				  struct dentry *parent);
165extern void relay_close(struct rchan *chan);
166extern void relay_flush(struct rchan *chan);
167extern void relay_subbufs_consumed(struct rchan *chan,
168				   unsigned int cpu,
169				   size_t consumed);
170extern void relay_reset(struct rchan *chan);
171extern int relay_buf_full(struct rchan_buf *buf);
172
173extern size_t relay_switch_subbuf(struct rchan_buf *buf,
174				  size_t length);
175
176/**
177 *	relay_write - write data into the channel
178 *	@chan: relay channel
179 *	@data: data to be written
180 *	@length: number of bytes to write
181 *
182 *	Writes data into the current cpu's channel buffer.
183 *
184 *	Protects the buffer by disabling interrupts.  Use this
185 *	if you might be logging from interrupt context.  Try
186 *	__relay_write() if you know you	won't be logging from
187 *	interrupt context.
188 */
189static inline void relay_write(struct rchan *chan,
190			       const void *data,
191			       size_t length)
192{
193	unsigned long flags;
194	struct rchan_buf *buf;
195
196	local_irq_save(flags);
197	buf = *this_cpu_ptr(chan->buf);
198	if (unlikely(buf->offset + length > chan->subbuf_size))
199		length = relay_switch_subbuf(buf, length);
200	memcpy(buf->data + buf->offset, data, length);
201	buf->offset += length;
202	local_irq_restore(flags);
203}
204
205/**
206 *	__relay_write - write data into the channel
207 *	@chan: relay channel
208 *	@data: data to be written
209 *	@length: number of bytes to write
210 *
211 *	Writes data into the current cpu's channel buffer.
212 *
213 *	Protects the buffer by disabling preemption.  Use
214 *	relay_write() if you might be logging from interrupt
215 *	context.
216 */
217static inline void __relay_write(struct rchan *chan,
218				 const void *data,
219				 size_t length)
220{
221	struct rchan_buf *buf;
222
223	buf = *get_cpu_ptr(chan->buf);
224	if (unlikely(buf->offset + length > buf->chan->subbuf_size))
225		length = relay_switch_subbuf(buf, length);
226	memcpy(buf->data + buf->offset, data, length);
227	buf->offset += length;
228	put_cpu_ptr(chan->buf);
229}
230
231/**
232 *	relay_reserve - reserve slot in channel buffer
233 *	@chan: relay channel
234 *	@length: number of bytes to reserve
235 *
236 *	Returns pointer to reserved slot, NULL if full.
237 *
238 *	Reserves a slot in the current cpu's channel buffer.
239 *	Does not protect the buffer at all - caller must provide
240 *	appropriate synchronization.
241 */
242static inline void *relay_reserve(struct rchan *chan, size_t length)
243{
244	void *reserved = NULL;
245	struct rchan_buf *buf = *get_cpu_ptr(chan->buf);
246
247	if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
248		length = relay_switch_subbuf(buf, length);
249		if (!length)
250			goto end;
251	}
252	reserved = buf->data + buf->offset;
253	buf->offset += length;
254
255end:
256	put_cpu_ptr(chan->buf);
257	return reserved;
258}
259
260/**
261 *	subbuf_start_reserve - reserve bytes at the start of a sub-buffer
262 *	@buf: relay channel buffer
263 *	@length: number of bytes to reserve
264 *
265 *	Helper function used to reserve bytes at the beginning of
266 *	a sub-buffer in the subbuf_start() callback.
267 */
268static inline void subbuf_start_reserve(struct rchan_buf *buf,
269					size_t length)
270{
271	BUG_ON(length >= buf->chan->subbuf_size - 1);
272	buf->offset = length;
273}
274
275/*
276 * exported relay file operations, kernel/relay.c
277 */
278extern const struct file_operations relay_file_operations;
279
280#ifdef CONFIG_RELAY
281int relay_prepare_cpu(unsigned int cpu);
282#else
283#define relay_prepare_cpu     NULL
284#endif
285
286#endif /* _LINUX_RELAY_H */
287
288