libringbuffer/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-align.h>
  20 #include <lttng/ust-compiler.h>
  21 #include <lttng/ust-tracer.h>
  22
  23 struct lttng_ust_lib_ring_buffer;
  24 struct lttng_ust_lib_ring_buffer_channel;
  25 struct lttng_ust_lib_ring_buffer_config;
  26 struct lttng_ust_lib_ring_buffer_ctx;
  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_lib_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_lib_ring_buffer_channel *chan);
  40         size_t (*record_header_size) (const struct lttng_ust_lib_ring_buffer_config *config,
  41                                       struct lttng_ust_lib_ring_buffer_channel *chan,
  42                                       size_t offset,
  43                                       size_t *pre_header_padding,
  44                                       struct lttng_ust_lib_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_lib_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_lib_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_lib_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_lib_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_lib_ring_buffer_config *config,
  76                             struct lttng_ust_lib_ring_buffer_channel *chan,
  77                             struct lttng_ust_lib_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_lib_ring_buffer_config *config,
  85                                 size_t *offset, size_t *length);
  86         void (*packet_size_field) (const struct lttng_ust_lib_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. Tracing must be performed
 100  *   with preemption disabled (lib_ring_buffer_get_cpu() and
 101  *   lib_ring_buffer_put_cpu()).
 102  *
 103  * RING_BUFFER_ALLOC_PER_CPU and RING_BUFFER_SYNC_GLOBAL :
 104  *   Per-cpu buffer with global synchronization. Tracing can be performed with
 105  *   preemption enabled, statistically stays on the local buffers.
 106  *
 107  * RING_BUFFER_ALLOC_GLOBAL and RING_BUFFER_SYNC_PER_CPU :
 108  *   Should only be used for buffers belonging to a single thread or protected
 109  *   by mutual exclusion by the client. Note that periodical sub-buffer switch
 110  *   should be disabled in this kind of configuration.
 111  *
 112  * RING_BUFFER_ALLOC_GLOBAL and RING_BUFFER_SYNC_GLOBAL :
 113  *   Global shared buffer with global synchronization.
 114  *
 115  * wakeup:
 116  *
 117  * RING_BUFFER_WAKEUP_BY_TIMER uses per-cpu deferrable timers to poll the
 118  * buffers and wake up readers if data is ready. Mainly useful for tracers which
 119  * don't want to call into the wakeup code on the tracing path. Use in
 120  * combination with "read_timer_interval" channel_create() argument.
 121  *
 122  * RING_BUFFER_WAKEUP_BY_WRITER directly wakes up readers when a subbuffer is
 123  * ready to read. Lower latencies before the reader is woken up. Mainly suitable
 124  * for drivers.
 125  *
 126  * RING_BUFFER_WAKEUP_NONE does not perform any wakeup whatsoever. The client
 127  * has the responsibility to perform wakeups.
 128  */
 129 #define LTTNG_UST_RING_BUFFER_CONFIG_PADDING    20
 130
 131 enum lttng_ust_lib_ring_buffer_alloc_types {
 132         RING_BUFFER_ALLOC_PER_CPU,
 133         RING_BUFFER_ALLOC_GLOBAL,
 134 };
 135
 136 enum lttng_ust_lib_ring_buffer_sync_types {
 137         RING_BUFFER_SYNC_PER_CPU,       /* Wait-free */
 138         RING_BUFFER_SYNC_GLOBAL,        /* Lock-free */
 139 };
 140
 141 enum lttng_ust_lib_ring_buffer_mode_types {
 142         RING_BUFFER_OVERWRITE = 0,      /* Overwrite when buffer full */
 143         RING_BUFFER_DISCARD = 1,        /* Discard when buffer full */
 144 };
 145
 146 enum lttng_ust_lib_ring_buffer_output_types {
 147         RING_BUFFER_SPLICE,
 148         RING_BUFFER_MMAP,
 149         RING_BUFFER_READ,               /* TODO */
 150         RING_BUFFER_ITERATOR,
 151         RING_BUFFER_NONE,
 152 };
 153
 154 enum lttng_ust_lib_ring_buffer_backend_types {
 155         RING_BUFFER_PAGE,
 156         RING_BUFFER_VMAP,               /* TODO */
 157         RING_BUFFER_STATIC,             /* TODO */
 158 };
 159
 160 enum lttng_ust_lib_ring_buffer_oops_types {
 161         RING_BUFFER_NO_OOPS_CONSISTENCY,
 162         RING_BUFFER_OOPS_CONSISTENCY,
 163 };
 164
 165 enum lttng_ust_lib_ring_buffer_ipi_types {
 166         RING_BUFFER_IPI_BARRIER,
 167         RING_BUFFER_NO_IPI_BARRIER,
 168 };
 169
 170 enum lttng_ust_lib_ring_buffer_wakeup_types {
 171         RING_BUFFER_WAKEUP_BY_TIMER,    /* wake up performed by timer */
 172         RING_BUFFER_WAKEUP_BY_WRITER,   /*
 173                                          * writer wakes up reader,
 174                                          * not lock-free
 175                                          * (takes spinlock).
 176                                          */
 177 };
 178
 179 struct lttng_ust_lib_ring_buffer_config {
 180         enum lttng_ust_lib_ring_buffer_alloc_types alloc;
 181         enum lttng_ust_lib_ring_buffer_sync_types sync;
 182         enum lttng_ust_lib_ring_buffer_mode_types mode;
 183         enum lttng_ust_lib_ring_buffer_output_types output;
 184         enum lttng_ust_lib_ring_buffer_backend_types backend;
 185         enum lttng_ust_lib_ring_buffer_oops_types oops;
 186         enum lttng_ust_lib_ring_buffer_ipi_types ipi;
 187         enum lttng_ust_lib_ring_buffer_wakeup_types wakeup;
 188         /*
 189          * tsc_bits: timestamp bits saved at each record.
 190          *   0 and 64 disable the timestamp compression scheme.
 191          */
 192         unsigned int tsc_bits;
 193         struct lttng_ust_lib_ring_buffer_client_cb cb;
 194         /*
 195          * client_type is used by the consumer process (which is in a
 196          * different address space) to lookup the appropriate client
 197          * callbacks and update the cb pointers.
 198          */
 199         int client_type;
 200         int _unused1;
 201         const struct lttng_ust_lib_ring_buffer_client_cb *cb_ptr;
 202         char padding[LTTNG_UST_RING_BUFFER_CONFIG_PADDING];
 203 };
 204
 205 /*
 206  * Reservation flags.
 207  *
 208  * RING_BUFFER_RFLAG_FULL_TSC
 209  *
 210  * This flag is passed to record_header_size() and to the primitive used to
 211  * write the record header. It indicates that the full 64-bit time value is
 212  * needed in the record header. If this flag is not set, the record header needs
 213  * only to contain "tsc_bits" bit of time value.
 214  *
 215  * Reservation flags can be added by the client, starting from
 216  * "(RING_BUFFER_FLAGS_END << 0)". It can be used to pass information from
 217  * record_header_size() to lib_ring_buffer_write_record_header().
 218  */
 219 #define RING_BUFFER_RFLAG_FULL_TSC              (1U << 0)
 220 #define RING_BUFFER_RFLAG_END                   (1U << 1)
 221
 222 /*
 223  * lib_ring_buffer_check_config() returns 0 on success.
 224  * Used internally to check for valid configurations at channel creation.
 225  */
 226 static inline lttng_ust_notrace
 227 int lib_ring_buffer_check_config(const struct lttng_ust_lib_ring_buffer_config *config,
 228                              unsigned int switch_timer_interval,
 229                              unsigned int read_timer_interval);
 230 static inline
 231 int lib_ring_buffer_check_config(const struct lttng_ust_lib_ring_buffer_config *config,
 232                              unsigned int switch_timer_interval,
 233                              unsigned int read_timer_interval)
 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 */