diff options
Diffstat (limited to 'xen/include/public/trace.h')
| -rw-r--r-- | xen/include/public/trace.h | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/xen/include/public/trace.h b/xen/include/public/trace.h index 4cbb896342..21fe15ffb9 100644 --- a/xen/include/public/trace.h +++ b/xen/include/public/trace.h @@ -141,6 +141,14 @@ struct t_rec { * field, indexes into an array of struct t_rec's. */ struct t_buf { + /* Assume the data buffer size is X. X is generally not a power of 2. + * CONS and PROD are incremented modulo (2*X): + * 0 <= cons < 2*X + * 0 <= prod < 2*X + * This is done because addition modulo X breaks at 2^32 when X is not a + * power of 2: + * (((2^32 - 1) % X) + 1) % X != (2^32) % X + */ uint32_t cons; /* Offset of next item to be consumed by control tools. */ uint32_t prod; /* Offset of next item to be produced by Xen. */ /* Records follow immediately after the meta-data header. */ |