+++ /dev/null
-/* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only)
- *
- * lib/ringbuffer/frontend_api.h
- *
- * Ring Buffer Library Synchronization Header (buffer write API).
- *
- * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- *
- * See ring_buffer_frontend.c for more information on wait-free algorithms.
- * See linux/ringbuffer/frontend.h for channel allocation and read-side API.
- */
-
-#ifndef _LIB_RING_BUFFER_FRONTEND_API_H
-#define _LIB_RING_BUFFER_FRONTEND_API_H
-
-#include <wrapper/ringbuffer/frontend.h>
-#include <wrapper/percpu-defs.h>
-#include <linux/errno.h>
-#include <linux/prefetch.h>
-
-/**
- * lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit.
- *
- * Disables preemption (acts as a RCU read-side critical section) and keeps a
- * ring buffer nesting count as supplementary safety net to ensure tracer client
- * code will never trigger an endless recursion. Returns the processor ID on
- * success, -EPERM on failure (nesting count too high).
- *
- * asm volatile and "memory" clobber prevent the compiler from moving
- * instructions out of the ring buffer nesting count. This is required to ensure
- * that probe side-effects which can cause recursion (e.g. unforeseen traps,
- * divisions by 0, ...) are triggered within the incremented nesting count
- * section.
- */
-static inline
-int lib_ring_buffer_get_cpu(const struct lib_ring_buffer_config *config)
-{
- int cpu, nesting;
-
- rcu_read_lock_sched_notrace();
- cpu = smp_processor_id();
- nesting = ++per_cpu(lib_ring_buffer_nesting, cpu);
- barrier();
-
- if (unlikely(nesting > RING_BUFFER_MAX_NESTING)) {
- WARN_ON_ONCE(1);
- per_cpu(lib_ring_buffer_nesting, cpu)--;
- rcu_read_unlock_sched_notrace();
- return -EPERM;
- } else
- return cpu;
-}
-
-/**
- * lib_ring_buffer_put_cpu - Follows ring buffer reserve/commit.
- */
-static inline
-void lib_ring_buffer_put_cpu(const struct lib_ring_buffer_config *config)
-{
- barrier();
- (*lttng_this_cpu_ptr(&lib_ring_buffer_nesting))--;
- rcu_read_unlock_sched_notrace();
-}
-
-/*
- * lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not
- * part of the API per se.
- *
- * returns 0 if reserve ok, or 1 if the slow path must be taken.
- */
-static inline
-int lib_ring_buffer_try_reserve(const struct lib_ring_buffer_config *config,
- struct lib_ring_buffer_ctx *ctx,
- void *client_ctx,
- unsigned long *o_begin, unsigned long *o_end,
- unsigned long *o_old, size_t *before_hdr_pad)
-{
- struct channel *chan = ctx->chan;
- struct lib_ring_buffer *buf = ctx->buf;
- *o_begin = v_read(config, &buf->offset);
- *o_old = *o_begin;
-
- ctx->tsc = lib_ring_buffer_clock_read(chan);
- if ((int64_t) ctx->tsc == -EIO)
- return 1;
-
- /*
- * Prefetch cacheline for read because we have to read the previous
- * commit counter to increment it and commit seq value to compare it to
- * the commit counter.
- */
- prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]);
-
- if (last_tsc_overflow(config, buf, ctx->tsc))
- ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC;
-
- if (unlikely(subbuf_offset(*o_begin, chan) == 0))
- return 1;
-
- ctx->slot_size = record_header_size(config, chan, *o_begin,
- before_hdr_pad, ctx, client_ctx);
- ctx->slot_size +=
- lib_ring_buffer_align(*o_begin + ctx->slot_size,
- ctx->largest_align) + ctx->data_size;
- if (unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size)
- > chan->backend.subbuf_size))
- return 1;
-
- /*
- * Record fits in the current buffer and we are not on a switch
- * boundary. It's safe to write.
- */
- *o_end = *o_begin + ctx->slot_size;
-
- if (unlikely((subbuf_offset(*o_end, chan)) == 0))
- /*
- * The offset_end will fall at the very beginning of the next
- * subbuffer.
- */
- return 1;
-
- return 0;
-}
-
-/**
- * lib_ring_buffer_reserve - Reserve space in a ring buffer.
- * @config: ring buffer instance configuration.
- * @ctx: ring buffer context. (input and output) Must be already initialized.
- *
- * Atomic wait-free slot reservation. The reserved space starts at the context
- * "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc".
- *
- * Return :
- * 0 on success.
- * -EAGAIN if channel is disabled.
- * -ENOSPC if event size is too large for packet.
- * -ENOBUFS if there is currently not enough space in buffer for the event.
- * -EIO if data cannot be written into the buffer for any other reason.
- */
-
-static inline
-int lib_ring_buffer_reserve(const struct lib_ring_buffer_config *config,
- struct lib_ring_buffer_ctx *ctx,
- void *client_ctx)
-{
- struct channel *chan = ctx->chan;
- struct lib_ring_buffer *buf;
- unsigned long o_begin, o_end, o_old;
- size_t before_hdr_pad = 0;
-
- if (unlikely(atomic_read(&chan->record_disabled)))
- return -EAGAIN;
-
- if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
- buf = per_cpu_ptr(chan->backend.buf, ctx->cpu);
- else
- buf = chan->backend.buf;
- if (unlikely(atomic_read(&buf->record_disabled)))
- return -EAGAIN;
- ctx->buf = buf;
-
- /*
- * Perform retryable operations.
- */
- if (unlikely(lib_ring_buffer_try_reserve(config, ctx, client_ctx, &o_begin,
- &o_end, &o_old, &before_hdr_pad)))
- goto slow_path;
-
- if (unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end)
- != o_old))
- goto slow_path;
-
- /*
- * Atomically update last_tsc. This update races against concurrent
- * atomic updates, but the race will always cause supplementary full TSC
- * record headers, never the opposite (missing a full TSC record header
- * when it would be needed).
- */
- save_last_tsc(config, ctx->buf, ctx->tsc);
-
- /*
- * Push the reader if necessary
- */
- lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1);
-
- /*
- * Clear noref flag for this subbuffer.
- */
- lib_ring_buffer_clear_noref(config, &ctx->buf->backend,
- subbuf_index(o_end - 1, chan));
-
- ctx->pre_offset = o_begin;
- ctx->buf_offset = o_begin + before_hdr_pad;
- return 0;
-slow_path:
- return lib_ring_buffer_reserve_slow(ctx, client_ctx);
-}
-
-/**
- * lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer.
- * @config: ring buffer instance configuration.
- * @buf: buffer
- * @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH)
- *
- * This operation is completely reentrant : can be called while tracing is
- * active with absolutely no lock held.
- *
- * Note, however, that as a v_cmpxchg is used for some atomic operations and
- * requires to be executed locally for per-CPU buffers, this function must be
- * called from the CPU which owns the buffer for a ACTIVE flush, with preemption
- * disabled, for RING_BUFFER_SYNC_PER_CPU configuration.
- */
-static inline
-void lib_ring_buffer_switch(const struct lib_ring_buffer_config *config,
- struct lib_ring_buffer *buf, enum switch_mode mode)
-{
- lib_ring_buffer_switch_slow(buf, mode);
-}
-
-/* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */
-
-/**
- * lib_ring_buffer_commit - Commit an record.
- * @config: ring buffer instance configuration.
- * @ctx: ring buffer context. (input arguments only)
- *
- * Atomic unordered slot commit. Increments the commit count in the
- * specified sub-buffer, and delivers it if necessary.
- */
-static inline
-void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
- const struct lib_ring_buffer_ctx *ctx)
-{
- struct channel *chan = ctx->chan;
- struct lib_ring_buffer *buf = ctx->buf;
- unsigned long offset_end = ctx->buf_offset;
- unsigned long endidx = subbuf_index(offset_end - 1, chan);
- unsigned long commit_count;
- struct commit_counters_hot *cc_hot = &buf->commit_hot[endidx];
-
- /*
- * Must count record before incrementing the commit count.
- */
- subbuffer_count_record(config, &buf->backend, endidx);
-
- /*
- * Order all writes to buffer before the commit count update that will
- * determine that the subbuffer is full.
- */
- if (config->ipi == RING_BUFFER_IPI_BARRIER) {
- /*
- * Must write slot data before incrementing commit count. This
- * compiler barrier is upgraded into a smp_mb() by the IPI sent
- * by get_subbuf().
- */
- barrier();
- } else
- smp_wmb();
-
- v_add(config, ctx->slot_size, &cc_hot->cc);
-
- /*
- * commit count read can race with concurrent OOO commit count updates.
- * This is only needed for lib_ring_buffer_check_deliver (for
- * non-polling delivery only) and for
- * lib_ring_buffer_write_commit_counter. The race can only cause the
- * counter to be read with the same value more than once, which could
- * cause :
- * - Multiple delivery for the same sub-buffer (which is handled
- * gracefully by the reader code) if the value is for a full
- * sub-buffer. It's important that we can never miss a sub-buffer
- * delivery. Re-reading the value after the v_add ensures this.
- * - Reading a commit_count with a higher value that what was actually
- * added to it for the lib_ring_buffer_write_commit_counter call
- * (again caused by a concurrent committer). It does not matter,
- * because this function is interested in the fact that the commit
- * count reaches back the reserve offset for a specific sub-buffer,
- * which is completely independent of the order.
- */
- commit_count = v_read(config, &cc_hot->cc);
-
- lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
- commit_count, endidx, ctx->tsc);
- /*
- * Update used size at each commit. It's needed only for extracting
- * ring_buffer buffers from vmcore, after crash.
- */
- lib_ring_buffer_write_commit_counter(config, buf, chan,
- offset_end, commit_count, cc_hot);
-}
-
-/**
- * lib_ring_buffer_try_discard_reserve - Try discarding a record.
- * @config: ring buffer instance configuration.
- * @ctx: ring buffer context. (input arguments only)
- *
- * Only succeeds if no other record has been written after the record to
- * discard. If discard fails, the record must be committed to the buffer.
- *
- * Returns 0 upon success, -EPERM if the record cannot be discarded.
- */
-static inline
-int lib_ring_buffer_try_discard_reserve(const struct lib_ring_buffer_config *config,
- const struct lib_ring_buffer_ctx *ctx)
-{
- struct lib_ring_buffer *buf = ctx->buf;
- unsigned long end_offset = ctx->pre_offset + ctx->slot_size;
-
- /*
- * We need to ensure that if the cmpxchg succeeds and discards the
- * record, the next record will record a full TSC, because it cannot
- * rely on the last_tsc associated with the discarded record to detect
- * overflows. The only way to ensure this is to set the last_tsc to 0
- * (assuming no 64-bit TSC overflow), which forces to write a 64-bit
- * timestamp in the next record.
- *
- * Note: if discard fails, we must leave the TSC in the record header.
- * It is needed to keep track of TSC overflows for the following
- * records.
- */
- save_last_tsc(config, buf, 0ULL);
-
- if (likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset)
- != end_offset))
- return -EPERM;
- else
- return 0;
-}
-
-static inline
-void channel_record_disable(const struct lib_ring_buffer_config *config,
- struct channel *chan)
-{
- atomic_inc(&chan->record_disabled);
-}
-
-static inline
-void channel_record_enable(const struct lib_ring_buffer_config *config,
- struct channel *chan)
-{
- atomic_dec(&chan->record_disabled);
-}
-
-static inline
-void lib_ring_buffer_record_disable(const struct lib_ring_buffer_config *config,
- struct lib_ring_buffer *buf)
-{
- atomic_inc(&buf->record_disabled);
-}
-
-static inline
-void lib_ring_buffer_record_enable(const struct lib_ring_buffer_config *config,
- struct lib_ring_buffer *buf)
-{
- atomic_dec(&buf->record_disabled);
-}
-
-#endif /* _LIB_RING_BUFFER_FRONTEND_API_H */
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