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