include/ringbuffer/config.h

   1 /* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only)
   2  *
   3  * ringbuffer/config.h
   4  *
   5  * Ring buffer configuration header. Note: after declaring the standard inline
   6  * functions, clients should also include linux/ringbuffer/api.h.
   7  *
   8  * Copyright (C) 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   9  */
  10
  11 #ifndef _LIB_RING_BUFFER_CONFIG_H
  12 #define _LIB_RING_BUFFER_CONFIG_H
  13
  14 #include <linux/types.h>
  15 #include <linux/percpu.h>
  16 #include <lttng/align.h>
  17 #include <lttng/tracer-core.h>
  18
  19 struct lttng_kernel_ring_buffer;
  20 struct lttng_kernel_ring_buffer_channel;
  21 struct lttng_kernel_ring_buffer_config;
  22 struct lttng_kernel_ring_buffer_ctx;
  23 struct lttng_kernel_ring_buffer_ctx_private;
  24
  25 /*
  26  * Ring buffer client callbacks. Only used by slow path, never on fast path.
  27  * For the fast path, record_header_size(), ring_buffer_clock_read() should be
  28  * provided as inline functions too.  These may simply return 0 if not used by
  29  * the client.
  30  */
  31 struct lttng_kernel_ring_buffer_client_cb {
  32         /* Mandatory callbacks */
  33
  34         /* A static inline version is also required for fast path */
  35         u64 (*ring_buffer_clock_read) (struct lttng_kernel_ring_buffer_channel *chan);
  36         size_t (*record_header_size) (const struct lttng_kernel_ring_buffer_config *config,
  37                                       struct lttng_kernel_ring_buffer_channel *chan, size_t offset,
  38                                       size_t *pre_header_padding,
  39                                       struct lttng_kernel_ring_buffer_ctx *ctx,
  40                                       void *client_ctx);
  41
  42         /* Slow path only, at subbuffer switch */
  43         size_t (*subbuffer_header_size) (void);
  44         void (*buffer_begin) (struct lttng_kernel_ring_buffer *buf, u64 tsc,
  45                               unsigned int subbuf_idx);
  46         void (*buffer_end) (struct lttng_kernel_ring_buffer *buf, u64 tsc,
  47                             unsigned int subbuf_idx, unsigned long data_size);
  48
  49         /* Optional callbacks (can be set to NULL) */
  50
  51         /* Called at buffer creation/finalize */
  52         int (*buffer_create) (struct lttng_kernel_ring_buffer *buf, void *priv,
  53                               int cpu, const char *name);
  54         /*
  55          * Clients should guarantee that no new reader handle can be opened
  56          * after finalize.
  57          */
  58         void (*buffer_finalize) (struct lttng_kernel_ring_buffer *buf, void *priv, int cpu);
  59
  60         /*
  61          * Extract header length, payload length and timestamp from event
  62          * record. Used by buffer iterators. Timestamp is only used by channel
  63          * iterator.
  64          */
  65         void (*record_get) (const struct lttng_kernel_ring_buffer_config *config,
  66                             struct lttng_kernel_ring_buffer_channel *chan, struct lttng_kernel_ring_buffer *buf,
  67                             size_t offset, size_t *header_len,
  68                             size_t *payload_len, u64 *timestamp);
  69 };
  70
  71 /*
  72  * Ring buffer instance configuration.
  73  *
  74  * Declare as "static const" within the client object to ensure the inline fast
  75  * paths can be optimized.
  76  *
  77  * alloc/sync pairs:
  78  *
  79  * RING_BUFFER_ALLOC_PER_CPU and RING_BUFFER_SYNC_PER_CPU :
  80  *   Per-cpu buffers with per-cpu synchronization. Tracing must be performed
  81  *   with preemption disabled (lib_ring_buffer_get_cpu() and
  82  *   lib_ring_buffer_put_cpu()).
  83  *
  84  * RING_BUFFER_ALLOC_PER_CPU and RING_BUFFER_SYNC_GLOBAL :
  85  *   Per-cpu buffer with global synchronization. Tracing can be performed with
  86  *   preemption enabled, statistically stays on the local buffers.
  87  *
  88  * RING_BUFFER_ALLOC_GLOBAL and RING_BUFFER_SYNC_PER_CPU :
  89  *   Should only be used for buffers belonging to a single thread or protected
  90  *   by mutual exclusion by the client. Note that periodical sub-buffer switch
  91  *   should be disabled in this kind of configuration.
  92  *
  93  * RING_BUFFER_ALLOC_GLOBAL and RING_BUFFER_SYNC_GLOBAL :
  94  *   Global shared buffer with global synchronization.
  95  *
  96  * wakeup:
  97  *
  98  * RING_BUFFER_WAKEUP_BY_TIMER uses per-cpu timers to poll the
  99  * buffers and wake up readers if data is ready. Mainly useful for tracers which
 100  * don't want to call into the wakeup code on the tracing path. Use in
 101  * combination with "read_timer_interval" channel_create() argument.
 102  *
 103  * RING_BUFFER_WAKEUP_BY_WRITER directly wakes up readers when a subbuffer is
 104  * ready to read. Lower latencies before the reader is woken up. Mainly suitable
 105  * for drivers. Going through an "irq_work" allows triggering this type of wakeup
 106  * even from NMI context: the wakeup will be slightly delayed until the next
 107  * interrupts are handled.
 108  *
 109  * RING_BUFFER_WAKEUP_NONE does not perform any wakeup whatsoever. The client
 110  * has the responsibility to perform wakeups.
 111  */
 112 struct lttng_kernel_ring_buffer_config {
 113         enum {
 114                 RING_BUFFER_ALLOC_PER_CPU,
 115                 RING_BUFFER_ALLOC_GLOBAL,
 116         } alloc;
 117         enum {
 118                 RING_BUFFER_SYNC_PER_CPU,       /* Wait-free */
 119                 RING_BUFFER_SYNC_GLOBAL,        /* Lock-free */
 120         } sync;
 121         enum {
 122                 RING_BUFFER_OVERWRITE,          /* Overwrite when buffer full */
 123                 RING_BUFFER_DISCARD,            /* Discard when buffer full */
 124         } mode;
 125         enum {
 126                 RING_BUFFER_SPLICE,
 127                 RING_BUFFER_MMAP,
 128                 RING_BUFFER_READ,               /* TODO */
 129                 RING_BUFFER_ITERATOR,
 130                 RING_BUFFER_NONE,
 131         } output;
 132         enum {
 133                 RING_BUFFER_PAGE,
 134                 RING_BUFFER_VMAP,               /* TODO */
 135                 RING_BUFFER_STATIC,             /* TODO */
 136         } backend;
 137         enum {
 138                 RING_BUFFER_NO_OOPS_CONSISTENCY,
 139                 RING_BUFFER_OOPS_CONSISTENCY,
 140         } oops;
 141         enum {
 142                 RING_BUFFER_IPI_BARRIER,
 143                 RING_BUFFER_NO_IPI_BARRIER,
 144         } ipi;
 145         enum {
 146                 RING_BUFFER_WAKEUP_BY_TIMER,    /* wake up performed by timer */
 147                 RING_BUFFER_WAKEUP_BY_WRITER,   /*
 148                                                  * writer wakes up reader through
 149                                                  * irq_work.
 150                                                  */
 151         } wakeup;
 152         /*
 153          * tsc_bits: timestamp bits saved at each record.
 154          *   0 and 64 disable the timestamp compression scheme.
 155          */
 156         unsigned int tsc_bits;
 157         struct lttng_kernel_ring_buffer_client_cb cb;
 158 };
 159
 160 /*
 161  * ring buffer private context
 162  *
 163  * Private context passed to lib_ring_buffer_reserve(), lib_ring_buffer_commit(),
 164  * lib_ring_buffer_try_discard_reserve(), lib_ring_buffer_align_ctx() and
 165  * lib_ring_buffer_write().
 166  *
 167  * Get struct lttng_kernel_ring_buffer_ctx parent with container_of().
 168  */
 169
 170 struct lttng_kernel_ring_buffer_ctx_private {
 171         /* input received by lib_ring_buffer_reserve(). */
 172         struct lttng_kernel_ring_buffer_channel *chan;                  /* ring buffer channel */
 173
 174         /* output from lib_ring_buffer_reserve() */
 175         int reserve_cpu;                        /* processor id updated by the reserve */
 176         size_t slot_size;                       /* size of the reserved slot */
 177         unsigned long buf_offset;               /* offset following the record header */
 178         unsigned long pre_offset;               /*
 179                                                  * Initial offset position _before_
 180                                                  * the record is written. Positioned
 181                                                  * prior to record header alignment
 182                                                  * padding.
 183                                                  */
 184         u64 tsc;                                /* time-stamp counter value */
 185         unsigned int rflags;                    /* reservation flags */
 186
 187         struct lttng_kernel_ring_buffer *buf;           /*
 188                                                  * buffer corresponding to processor id
 189                                                  * for this channel
 190                                                  */
 191         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 192 };
 193
 194 /*
 195  * ring buffer context
 196  *
 197  * Context passed to lib_ring_buffer_reserve(), lib_ring_buffer_commit(),
 198  * lib_ring_buffer_try_discard_reserve(), lib_ring_buffer_align_ctx() and
 199  * lib_ring_buffer_write().
 200  */
 201 struct lttng_kernel_ring_buffer_ctx {
 202         /* Private ring buffer context, set by reserve callback. */
 203         struct lttng_kernel_ring_buffer_ctx_private priv;
 204
 205         /* input received by lib_ring_buffer_reserve(), saved here. */
 206         void *client_priv;              /* Ring buffer client private data */
 207
 208         size_t data_size;               /* size of payload */
 209         int largest_align;              /*
 210                                          * alignment of the largest element
 211                                          * in the payload
 212                                          */
 213         struct lttng_kernel_probe_ctx *probe_ctx;       /* Probe context */
 214 };
 215
 216 /**
 217  * lib_ring_buffer_ctx_init - initialize ring buffer context
 218  * @ctx: ring buffer context to initialize
 219  * @client_priv: client private data
 220  * @data_size: size of record data payload. It must be greater than 0.
 221  * @largest_align: largest alignment within data payload types
 222  */
 223 static inline
 224 void lib_ring_buffer_ctx_init(struct lttng_kernel_ring_buffer_ctx *ctx,
 225                               void *client_priv,
 226                               size_t data_size, int largest_align,
 227                               struct lttng_kernel_probe_ctx *probe_ctx)
 228 {
 229         ctx->client_priv = client_priv;
 230         ctx->data_size = data_size;
 231         ctx->largest_align = largest_align;
 232         ctx->probe_ctx = probe_ctx;
 233 }
 234
 235 /*
 236  * Reservation flags.
 237  *
 238  * RING_BUFFER_RFLAG_FULL_TSC
 239  *
 240  * This flag is passed to record_header_size() and to the primitive used to
 241  * write the record header. It indicates that the full 64-bit time value is
 242  * needed in the record header. If this flag is not set, the record header needs
 243  * only to contain "tsc_bits" bit of time value.
 244  *
 245  * Reservation flags can be added by the client, starting from
 246  * "(RING_BUFFER_FLAGS_END << 0)". It can be used to pass information from
 247  * record_header_size() to lib_ring_buffer_write_record_header().
 248  */
 249 #define RING_BUFFER_RFLAG_FULL_TSC              (1U << 0)
 250 #define RING_BUFFER_RFLAG_END                   (1U << 1)
 251
 252 #ifndef LTTNG_TRACER_CORE_H
 253 #error "lttng/tracer-core.h is needed for RING_BUFFER_ALIGN define"
 254 #endif
 255
 256 /*
 257  * We need to define RING_BUFFER_ALIGN_ATTR so it is known early at
 258  * compile-time. We have to duplicate the "config->align" information and the
 259  * definition here because config->align is used both in the slow and fast
 260  * paths, but RING_BUFFER_ALIGN_ATTR is only available for the client code.
 261  */
 262 #ifdef RING_BUFFER_ALIGN
 263
 264 # define RING_BUFFER_ALIGN_ATTR         /* Default arch alignment */
 265
 266 /*
 267  * Calculate the offset needed to align the type.
 268  * size_of_type must be non-zero.
 269  */
 270 static inline
 271 unsigned int lib_ring_buffer_align(size_t align_drift, size_t size_of_type)
 272 {
 273         return offset_align(align_drift, size_of_type);
 274 }
 275
 276 #else
 277
 278 # define RING_BUFFER_ALIGN_ATTR __attribute__((packed))
 279
 280 /*
 281  * Calculate the offset needed to align the type.
 282  * size_of_type must be non-zero.
 283  */
 284 static inline
 285 unsigned int lib_ring_buffer_align(size_t align_drift, size_t size_of_type)
 286 {
 287         return 0;
 288 }
 289
 290 #endif
 291
 292 /**
 293  * lib_ring_buffer_align_ctx - Align context offset on "alignment"
 294  * @ctx: ring buffer context.
 295  */
 296 static inline
 297 void lib_ring_buffer_align_ctx(struct lttng_kernel_ring_buffer_ctx *ctx,
 298                            size_t alignment)
 299 {
 300         ctx->priv.buf_offset += lib_ring_buffer_align(ctx->priv.buf_offset,
 301                                                  alignment);
 302 }
 303
 304 /*
 305  * lib_ring_buffer_check_config() returns 0 on success.
 306  * Used internally to check for valid configurations at channel creation.
 307  */
 308 static inline
 309 int lib_ring_buffer_check_config(const struct lttng_kernel_ring_buffer_config *config,
 310                              unsigned int switch_timer_interval,
 311                              unsigned int read_timer_interval)
 312 {
 313         if (config->alloc == RING_BUFFER_ALLOC_GLOBAL
 314             && config->sync == RING_BUFFER_SYNC_PER_CPU
 315             && switch_timer_interval)
 316                 return -EINVAL;
 317         return 0;
 318 }
 319
 320 #include <ringbuffer/vatomic.h>
 321
 322 #endif /* _LIB_RING_BUFFER_CONFIG_H */