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   */
34  struct 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   */
59  struct 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   */
80  struct 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  
156  struct 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);
162  extern int relay_late_setup_files(struct rchan *chan,
163  				  const char *base_filename,
164  				  struct dentry *parent);
165  extern void relay_close(struct rchan *chan);
166  extern void relay_flush(struct rchan *chan);
167  extern void relay_subbufs_consumed(struct rchan *chan,
168  				   unsigned int cpu,
169  				   size_t consumed);
170  extern void relay_reset(struct rchan *chan);
171  extern int relay_buf_full(struct rchan_buf *buf);
172  
173  extern 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   */
relay_write(struct rchan * chan,const void * data,size_t length)189  static 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   */
__relay_write(struct rchan * chan,const void * data,size_t length)217  static 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   */
relay_reserve(struct rchan * chan,size_t length)242  static 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  
255  end:
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   */
subbuf_start_reserve(struct rchan_buf * buf,size_t length)268  static 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   */
278  extern const struct file_operations relay_file_operations;
279  
280  #ifdef CONFIG_RELAY
281  int relay_prepare_cpu(unsigned int cpu);
282  #else
283  #define relay_prepare_cpu     NULL
284  #endif
285  
286  #endif /* _LINUX_RELAY_H */
287  
288