relay.h

  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 * Relay buffer statistics
 33 */
 34enum {
 35	RELAY_STATS_BUF_FULL = (1 << 0),
 36	RELAY_STATS_WRT_BIG = (1 << 1),
 37
 38	RELAY_STATS_LAST = RELAY_STATS_WRT_BIG,
 39};
 40
 41struct rchan_buf_stats
 42{
 43	unsigned int full_count;	/* counter for buffer full */
 44	unsigned int big_count;		/* counter for too big to write */
 45};
 46
 47/*
 48 * Per-cpu relay channel buffer
 49 */
 50struct rchan_buf
 51{
 52	void *start;			/* start of channel buffer */
 53	void *data;			/* start of current sub-buffer */
 54	size_t offset;			/* current offset into sub-buffer */
 55	size_t subbufs_produced;	/* count of sub-buffers produced */
 56	size_t subbufs_consumed;	/* count of sub-buffers consumed */
 57	struct rchan *chan;		/* associated channel */
 58	wait_queue_head_t read_wait;	/* reader wait queue */
 59	struct irq_work wakeup_work;	/* reader wakeup */
 60	struct dentry *dentry;		/* channel file dentry */
 61	struct kref kref;		/* channel buffer refcount */
 62	struct rchan_buf_stats stats;	/* buffer stats */
 63	struct page **page_array;	/* array of current buffer pages */
 64	unsigned int page_count;	/* number of current buffer pages */
 65	unsigned int finalized;		/* buffer has been finalized */
 66	size_t *padding;		/* padding counts per sub-buffer */
 67	size_t bytes_consumed;		/* bytes consumed in cur read subbuf */
 68	size_t early_bytes;		/* bytes consumed before VFS inited */
 69	unsigned int cpu;		/* this buf's cpu */
 70} ____cacheline_aligned;
 71
 72/*
 73 * Relay channel data structure
 74 */
 75struct rchan
 76{
 77	u32 version;			/* the version of this struct */
 78	size_t subbuf_size;		/* sub-buffer size */
 79	size_t n_subbufs;		/* number of sub-buffers per buffer */
 80	size_t alloc_size;		/* total buffer size allocated */
 81	const struct rchan_callbacks *cb; /* client callbacks */
 82	struct kref kref;		/* channel refcount */
 83	void *private_data;		/* for user-defined data */
 84	struct rchan_buf * __percpu *buf; /* per-cpu channel buffers */
 85	int is_global;			/* One global buffer ? */
 86	struct list_head list;		/* for channel list */
 87	struct dentry *parent;		/* parent dentry passed to open */
 88	int has_base_filename;		/* has a filename associated? */
 89	char base_filename[NAME_MAX];	/* saved base filename */
 90};
 91
 92/*
 93 * Relay channel client callbacks
 94 */
 95struct rchan_callbacks
 96{
 97	/*
 98	 * subbuf_start - called on buffer-switch to a new sub-buffer
 99	 * @buf: the channel buffer containing the new sub-buffer
100	 * @subbuf: the start of the new sub-buffer
101	 * @prev_subbuf: the start of the previous sub-buffer
102	 *
103	 * The client should return 1 to continue logging, 0 to stop
104	 * logging.
105	 *
106	 * This callback is optional.
107	 *
108	 * NOTE: subbuf_start will also be invoked when the buffer is
109	 *       created, so that the first sub-buffer can be initialized
110	 *       if necessary.  In this case, prev_subbuf will be NULL.
111	 *
112	 * NOTE: the client can reserve bytes at the beginning of the new
113	 *       sub-buffer by calling subbuf_start_reserve() in this callback.
114	 */
115	int (*subbuf_start) (struct rchan_buf *buf,
116			     void *subbuf,
117			     void *prev_subbuf);
118
119	/*
120	 * create_buf_file - create file to represent a relay channel buffer
121	 * @filename: the name of the file to create
122	 * @parent: the parent of the file to create
123	 * @mode: the mode of the file to create
124	 * @buf: the channel buffer
125	 * @is_global: outparam - set non-zero if the buffer should be global
126	 *
127	 * Called during relay_open(), once for each per-cpu buffer,
128	 * to allow the client to create a file to be used to
129	 * represent the corresponding channel buffer.  If the file is
130	 * created outside of relay, the parent must also exist in
131	 * that filesystem.
132	 *
133	 * The callback should return the dentry of the file created
134	 * to represent the relay buffer.
135	 *
136	 * Setting the is_global outparam to a non-zero value will
137	 * cause relay_open() to create a single global buffer rather
138	 * than the default set of per-cpu buffers.
139	 *
140	 * This callback is mandatory.
141	 *
142	 * See Documentation/filesystems/relay.rst for more info.
143	 */
144	struct dentry *(*create_buf_file)(const char *filename,
145					  struct dentry *parent,
146					  umode_t mode,
147					  struct rchan_buf *buf,
148					  int *is_global);
149
150	/*
151	 * remove_buf_file - remove file representing a relay channel buffer
152	 * @dentry: the dentry of the file to remove
153	 *
154	 * Called during relay_close(), once for each per-cpu buffer,
155	 * to allow the client to remove a file used to represent a
156	 * channel buffer.
157	 *
158	 * The callback should return 0 if successful, negative if not.
159	 *
160	 * This callback is mandatory.
161	 */
162	int (*remove_buf_file)(struct dentry *dentry);
163};
164
165/*
166 * CONFIG_RELAY kernel API, kernel/relay.c
167 */
168
169struct rchan *relay_open(const char *base_filename,
170			 struct dentry *parent,
171			 size_t subbuf_size,
172			 size_t n_subbufs,
173			 const struct rchan_callbacks *cb,
174			 void *private_data);
175extern void relay_close(struct rchan *chan);
176extern void relay_flush(struct rchan *chan);
177size_t relay_stats(struct rchan *chan, int flags);
178extern void relay_subbufs_consumed(struct rchan *chan,
179				   unsigned int cpu,
180				   size_t consumed);
181extern void relay_reset(struct rchan *chan);
182extern int relay_buf_full(struct rchan_buf *buf);
183
184extern size_t relay_switch_subbuf(struct rchan_buf *buf,
185				  size_t length);
186
187/**
188 *	relay_write - write data into the channel
189 *	@chan: relay channel
190 *	@data: data to be written
191 *	@length: number of bytes to write
192 *
193 *	Writes data into the current cpu's channel buffer.
194 *
195 *	Protects the buffer by disabling interrupts.  Use this
196 *	if you might be logging from interrupt context.  Try
197 *	__relay_write() if you know you	won't be logging from
198 *	interrupt context.
199 */
200static inline void relay_write(struct rchan *chan,
201			       const void *data,
202			       size_t length)
203{
204	unsigned long flags;
205	struct rchan_buf *buf;
206
207	local_irq_save(flags);
208	buf = *this_cpu_ptr(chan->buf);
209	if (unlikely(buf->offset + length > chan->subbuf_size))
210		length = relay_switch_subbuf(buf, length);
211	memcpy(buf->data + buf->offset, data, length);
212	buf->offset += length;
213	local_irq_restore(flags);
214}
215
216/**
217 *	__relay_write - write data into the channel
218 *	@chan: relay channel
219 *	@data: data to be written
220 *	@length: number of bytes to write
221 *
222 *	Writes data into the current cpu's channel buffer.
223 *
224 *	Protects the buffer by disabling preemption.  Use
225 *	relay_write() if you might be logging from interrupt
226 *	context.
227 */
228static inline void __relay_write(struct rchan *chan,
229				 const void *data,
230				 size_t length)
231{
232	struct rchan_buf *buf;
233
234	buf = *get_cpu_ptr(chan->buf);
235	if (unlikely(buf->offset + length > buf->chan->subbuf_size))
236		length = relay_switch_subbuf(buf, length);
237	memcpy(buf->data + buf->offset, data, length);
238	buf->offset += length;
239	put_cpu_ptr(chan->buf);
240}
241
242/**
243 *	relay_reserve - reserve slot in channel buffer
244 *	@chan: relay channel
245 *	@length: number of bytes to reserve
246 *
247 *	Returns pointer to reserved slot, NULL if full.
248 *
249 *	Reserves a slot in the current cpu's channel buffer.
250 *	Does not protect the buffer at all - caller must provide
251 *	appropriate synchronization.
252 */
253static inline void *relay_reserve(struct rchan *chan, size_t length)
254{
255	void *reserved = NULL;
256	struct rchan_buf *buf = *get_cpu_ptr(chan->buf);
257
258	if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
259		length = relay_switch_subbuf(buf, length);
260		if (!length)
261			goto end;
262	}
263	reserved = buf->data + buf->offset;
264	buf->offset += length;
265
266end:
267	put_cpu_ptr(chan->buf);
268	return reserved;
269}
270
271/**
272 *	subbuf_start_reserve - reserve bytes at the start of a sub-buffer
273 *	@buf: relay channel buffer
274 *	@length: number of bytes to reserve
275 *
276 *	Helper function used to reserve bytes at the beginning of
277 *	a sub-buffer in the subbuf_start() callback.
278 */
279static inline void subbuf_start_reserve(struct rchan_buf *buf,
280					size_t length)
281{
282	BUG_ON(length >= buf->chan->subbuf_size - 1);
283	buf->offset = length;
284}
285
286/*
287 * exported relay file operations, kernel/relay.c
288 */
289extern const struct file_operations relay_file_operations;
290
291#ifdef CONFIG_RELAY
292int relay_prepare_cpu(unsigned int cpu);
293#else
294#define relay_prepare_cpu     NULL
295#endif
296
297#endif /* _LINUX_RELAY_H */
298