src/common/ringbuffer/ringbuffer-config.h

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright (C) 2010-2021 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * Ring buffer configuration header. Note: after declaring the standard inline
   7  * functions, clients should also include linux/ringbuffer/api.h.
   8  */
   9
  10 #ifndef _LTTNG_RING_BUFFER_CONFIG_H
  11 #define _LTTNG_RING_BUFFER_CONFIG_H
  12
  13 #include <errno.h>
  14 #include <stdint.h>
  15 #include <stddef.h>
  16 #include <urcu/arch.h>
  17 #include <string.h>
  18
  19 #include <lttng/ust-utils.h>
  20 #include <lttng/ust-compiler.h>
  21 #include <lttng/ust-tracer.h>
  22
  23 struct lttng_ust_ring_buffer;
  24 struct lttng_ust_ring_buffer_channel;
  25 struct lttng_ust_ring_buffer_config;
  26 struct lttng_ust_ring_buffer_ctx_private;
  27 struct lttng_ust_shm_handle;
  28
  29 /*
  30  * Ring buffer client callbacks. Only used by slow path, never on fast path.
  31  * For the fast path, record_header_size(), ring_buffer_clock_read() should be
  32  * provided as inline functions too.  These may simply return 0 if not used by
  33  * the client.
  34  */
  35 struct lttng_ust_ring_buffer_client_cb {
  36         /* Mandatory callbacks */
  37
  38         /* A static inline version is also required for fast path */
  39         uint64_t (*ring_buffer_clock_read) (struct lttng_ust_ring_buffer_channel *chan);
  40         size_t (*record_header_size) (const struct lttng_ust_ring_buffer_config *config,
  41                                       struct lttng_ust_ring_buffer_channel *chan,
  42                                       size_t offset,
  43                                       size_t *pre_header_padding,
  44                                       struct lttng_ust_ring_buffer_ctx *ctx,
  45                                       void *client_ctx);
  46
  47         /* Slow path only, at subbuffer switch */
  48         size_t (*subbuffer_header_size) (void);
  49         void (*buffer_begin) (struct lttng_ust_ring_buffer *buf, uint64_t tsc,
  50                               unsigned int subbuf_idx,
  51                               struct lttng_ust_shm_handle *handle);
  52         void (*buffer_end) (struct lttng_ust_ring_buffer *buf, uint64_t tsc,
  53                             unsigned int subbuf_idx, unsigned long data_size,
  54                             struct lttng_ust_shm_handle *handle);
  55
  56         /* Optional callbacks (can be set to NULL) */
  57
  58         /* Called at buffer creation/finalize */
  59         int (*buffer_create) (struct lttng_ust_ring_buffer *buf, void *priv,
  60                               int cpu, const char *name,
  61                               struct lttng_ust_shm_handle *handle);
  62         /*
  63          * Clients should guarantee that no new reader handle can be opened
  64          * after finalize.
  65          */
  66         void (*buffer_finalize) (struct lttng_ust_ring_buffer *buf,
  67                                  void *priv, int cpu,
  68                                  struct lttng_ust_shm_handle *handle);
  69
  70         /*
  71          * Extract header length, payload length and timestamp from event
  72          * record. Used by buffer iterators. Timestamp is only used by channel
  73          * iterator.
  74          */
  75         void (*record_get) (const struct lttng_ust_ring_buffer_config *config,
  76                             struct lttng_ust_ring_buffer_channel *chan,
  77                             struct lttng_ust_ring_buffer *buf,
  78                             size_t offset, size_t *header_len,
  79                             size_t *payload_len, uint64_t *timestamp,
  80                             struct lttng_ust_shm_handle *handle);
  81         /*
  82          * Offset and size of content size field in client.
  83          */
  84         void (*content_size_field) (const struct lttng_ust_ring_buffer_config *config,
  85                                 size_t *offset, size_t *length);
  86         void (*packet_size_field) (const struct lttng_ust_ring_buffer_config *config,
  87                                 size_t *offset, size_t *length);
  88 };
  89
  90 /*
  91  * Ring buffer instance configuration.
  92  *
  93  * Declare as "static const" within the client object to ensure the inline fast
  94  * paths can be optimized.
  95  *
  96  * alloc/sync pairs:
  97  *
  98  * RING_BUFFER_ALLOC_PER_CPU and RING_BUFFER_SYNC_PER_CPU :
  99  *   Per-cpu buffers with per-cpu synchronization.
 100  *
 101  * RING_BUFFER_ALLOC_PER_CPU and RING_BUFFER_SYNC_GLOBAL :
 102  *   Per-cpu buffer with global synchronization. Tracing can be performed with
 103  *   preemption enabled, statistically stays on the local buffers.
 104  *
 105  * RING_BUFFER_ALLOC_GLOBAL and RING_BUFFER_SYNC_PER_CPU :
 106  *   Should only be used for buffers belonging to a single thread or protected
 107  *   by mutual exclusion by the client. Note that periodical sub-buffer switch
 108  *   should be disabled in this kind of configuration.
 109  *
 110  * RING_BUFFER_ALLOC_GLOBAL and RING_BUFFER_SYNC_GLOBAL :
 111  *   Global shared buffer with global synchronization.
 112  *
 113  * wakeup:
 114  *
 115  * RING_BUFFER_WAKEUP_BY_TIMER uses per-cpu deferrable timers to poll the
 116  * buffers and wake up readers if data is ready. Mainly useful for tracers which
 117  * don't want to call into the wakeup code on the tracing path. Use in
 118  * combination with "read_timer_interval" channel_create() argument.
 119  *
 120  * RING_BUFFER_WAKEUP_BY_WRITER directly wakes up readers when a subbuffer is
 121  * ready to read. Lower latencies before the reader is woken up. Mainly suitable
 122  * for drivers.
 123  *
 124  * RING_BUFFER_WAKEUP_NONE does not perform any wakeup whatsoever. The client
 125  * has the responsibility to perform wakeups.
 126  */
 127 #define LTTNG_UST_RING_BUFFER_CONFIG_PADDING    20
 128
 129 enum lttng_ust_ring_buffer_alloc_types {
 130         RING_BUFFER_ALLOC_PER_CPU,
 131         RING_BUFFER_ALLOC_GLOBAL,
 132 };
 133
 134 enum lttng_ust_ring_buffer_sync_types {
 135         RING_BUFFER_SYNC_PER_CPU,       /* Wait-free */
 136         RING_BUFFER_SYNC_GLOBAL,        /* Lock-free */
 137 };
 138
 139 enum lttng_ust_ring_buffer_mode_types {
 140         RING_BUFFER_OVERWRITE = 0,      /* Overwrite when buffer full */
 141         RING_BUFFER_DISCARD = 1,        /* Discard when buffer full */
 142 };
 143
 144 enum lttng_ust_ring_buffer_output_types {
 145         RING_BUFFER_SPLICE,
 146         RING_BUFFER_MMAP,
 147         RING_BUFFER_READ,               /* TODO */
 148         RING_BUFFER_ITERATOR,
 149         RING_BUFFER_NONE,
 150 };
 151
 152 enum lttng_ust_ring_buffer_backend_types {
 153         RING_BUFFER_PAGE,
 154         RING_BUFFER_VMAP,               /* TODO */
 155         RING_BUFFER_STATIC,             /* TODO */
 156 };
 157
 158 enum lttng_ust_ring_buffer_oops_types {
 159         RING_BUFFER_NO_OOPS_CONSISTENCY,
 160         RING_BUFFER_OOPS_CONSISTENCY,
 161 };
 162
 163 enum lttng_ust_ring_buffer_ipi_types {
 164         RING_BUFFER_IPI_BARRIER,
 165         RING_BUFFER_NO_IPI_BARRIER,
 166 };
 167
 168 enum lttng_ust_ring_buffer_wakeup_types {
 169         RING_BUFFER_WAKEUP_BY_TIMER,    /* wake up performed by timer */
 170         RING_BUFFER_WAKEUP_BY_WRITER,   /*
 171                                          * writer wakes up reader,
 172                                          * not lock-free
 173                                          * (takes spinlock).
 174                                          */
 175 };
 176
 177 struct lttng_ust_ring_buffer_config {
 178         enum lttng_ust_ring_buffer_alloc_types alloc;
 179         enum lttng_ust_ring_buffer_sync_types sync;
 180         enum lttng_ust_ring_buffer_mode_types mode;
 181         enum lttng_ust_ring_buffer_output_types output;
 182         enum lttng_ust_ring_buffer_backend_types backend;
 183         enum lttng_ust_ring_buffer_oops_types oops;
 184         enum lttng_ust_ring_buffer_ipi_types ipi;
 185         enum lttng_ust_ring_buffer_wakeup_types wakeup;
 186         /*
 187          * tsc_bits: timestamp bits saved at each record.
 188          *   0 and 64 disable the timestamp compression scheme.
 189          */
 190         unsigned int tsc_bits;
 191         struct lttng_ust_ring_buffer_client_cb cb;
 192         /*
 193          * client_type is used by the consumer process (which is in a
 194          * different address space) to lookup the appropriate client
 195          * callbacks and update the cb pointers.
 196          */
 197         int client_type;
 198         int _unused1;
 199         const struct lttng_ust_ring_buffer_client_cb *cb_ptr;
 200         char padding[LTTNG_UST_RING_BUFFER_CONFIG_PADDING];
 201 };
 202
 203 /*
 204  * Reservation flags.
 205  *
 206  * RING_BUFFER_RFLAG_FULL_TSC
 207  *
 208  * This flag is passed to record_header_size() and to the primitive used to
 209  * write the record header. It indicates that the full 64-bit time value is
 210  * needed in the record header. If this flag is not set, the record header needs
 211  * only to contain "tsc_bits" bit of time value.
 212  *
 213  * Reservation flags can be added by the client, starting from
 214  * "(RING_BUFFER_FLAGS_END << 0)". It can be used to pass information from
 215  * record_header_size() to lib_ring_buffer_write_record_header().
 216  */
 217 #define RING_BUFFER_RFLAG_FULL_TSC              (1U << 0)
 218 #define RING_BUFFER_RFLAG_END                   (1U << 1)
 219
 220 /*
 221  * lib_ring_buffer_check_config() returns 0 on success.
 222  * Used internally to check for valid configurations at channel creation.
 223  */
 224 static inline
 225 int lib_ring_buffer_check_config(const struct lttng_ust_ring_buffer_config *config,
 226                              unsigned int switch_timer_interval,
 227                              unsigned int read_timer_interval)
 228         lttng_ust_notrace;
 229
 230 static inline
 231 int lib_ring_buffer_check_config(const struct lttng_ust_ring_buffer_config *config,
 232                              unsigned int switch_timer_interval,
 233                              unsigned int read_timer_interval __attribute__((unused)))
 234 {
 235         if (config->alloc == RING_BUFFER_ALLOC_GLOBAL
 236             && config->sync == RING_BUFFER_SYNC_PER_CPU
 237             && switch_timer_interval)
 238                 return -EINVAL;
 239         return 0;
 240 }
 241
 242 #endif /* _LTTNG_RING_BUFFER_CONFIG_H */