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