Fix: refuse overwrite mode buffers with less than two subbuffers

[lttng-ust.git] / libringbuffer / ring_buffer_backend.c

diff --git a/libringbuffer/ring_buffer_backend.c b/libringbuffer/ring_buffer_backend.c
index 3db1f860f3918d8a1e61a959e1f4501678f93687..7d3a37809e73da27b25d43d8914ed285545075f7 100644 (file)
--- a/libringbuffer/ring_buffer_backend.c
+++ b/libringbuffer/ring_buffer_backend.c
@@ -234,6 +234,12 @@ int channel_backend_init(struct channel_backend *chanb,
                return -EINVAL;
        if (!num_subbuf || (num_subbuf & (num_subbuf - 1)))
                return -EINVAL;
+       /*
+        * Overwrite mode buffers require at least 2 subbuffers per
+        * buffer.
+        */
+       if (config->mode == RING_BUFFER_OVERWRITE && num_subbuf < 2)
+               return -EINVAL;
 
        ret = subbuffer_id_check_index(config, num_subbuf);
        if (ret)
@@ -425,8 +431,9 @@ int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb, si
  *
  * Return the address where a given offset is located (for read).
  * Should be used to get the current subbuffer header pointer. Given we know
- * it's never on a page boundary, it's safe to write directly to this address,
- * as long as the write is never bigger than a page size.
+ * it's never on a page boundary, it's safe to read/write directly
+ * from/to this address, as long as the read/write is never bigger than
+ * a page size.
  */
 void *lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
                                          size_t offset,