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(to: buf->data + buf->offset, from: data, len: 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(to: buf->data + buf->offset, from: data, len: 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
299