ring buffer context: cpu number becomes an output of reserve

[lttng-ust.git] / libringbuffer / frontend_api.h

diff --git a/libringbuffer/frontend_api.h b/libringbuffer/frontend_api.h
index fd601ce5ca93589636d6932cc435a3a1c8f1677b..96f79554b3764bb3cb40d140e34b5ebcebcc725e 100644 (file)
--- a/libringbuffer/frontend_api.h
+++ b/libringbuffer/frontend_api.h
@@ -18,12 +18,11 @@
 #include "frontend.h"
 
 /**
- * lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit.
+ * lib_ring_buffer_nesting_inc - Ring buffer recursive use protection.
  *
- * 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).
+ * The rint buffer buffer nesting count is a safety net to ensure tracer
+ * client code will never trigger an endless recursion.
+ * Returns 0 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
@@ -32,27 +31,22 @@
  * section.
  */
 static inline
-int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
+int lib_ring_buffer_nesting_inc(const struct lttng_ust_lib_ring_buffer_config *config)
 {
-       int cpu, nesting;
+       int nesting;
 
-       cpu = lttng_ust_get_cpu();
        nesting = ++URCU_TLS(lib_ring_buffer_nesting);
        cmm_barrier();
-
        if (caa_unlikely(nesting > 4)) {
                WARN_ON_ONCE(1);
                URCU_TLS(lib_ring_buffer_nesting)--;
                return -EPERM;
-       } else
-               return cpu;
+       }
+       return 0;
 }
 
-/**
- * lib_ring_buffer_put_cpu - Follows ring buffer reserve/commit.
- */
 static inline
-void lib_ring_buffer_put_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
+void lib_ring_buffer_nesting_dec(const struct lttng_ust_lib_ring_buffer_config *config)
 {
        cmm_barrier();
        URCU_TLS(lib_ring_buffer_nesting)--;            /* TLS */
@@ -148,10 +142,12 @@ int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *confi
        if (caa_unlikely(uatomic_read(&chan->record_disabled)))
                return -EAGAIN;
 
-       if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
-               buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp);
-       else
+       if (config->alloc == RING_BUFFER_ALLOC_PER_CPU) {
+               ctx->reserve_cpu = lttng_ust_get_cpu();
+               buf = shmp(handle, chan->backend.buf[ctx->reserve_cpu].shmp);
+       } else {
                buf = shmp(handle, chan->backend.buf[0].shmp);
+       }
        if (caa_unlikely(!buf))
                return -EIO;
        if (caa_unlikely(uatomic_read(&buf->record_disabled)))