From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
If the reader sub-buffer gets more data on it due to a writer still on the
reader sub-buffer, just updating the kbuf is not enough. An ioctl() needs to
be called again to update the "read" pointer, otherwise after reading the
full reader sub-buffer and calling the next ioctl(), the kernel will not
swap out for a new reader sub-buffer as it still thinks there's more to be
read.
Fixes: 2ed14b594f669 ("libtracefs: Add ring buffer memory mapping APIs")
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
src/tracefs-mmap.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/src/tracefs-mmap.c b/src/tracefs-mmap.c
index e0e37681e019..499233ae396c 100644
--- a/src/tracefs-mmap.c
+++ b/src/tracefs-mmap.c
@@ -143,6 +143,11 @@ __hidden void trace_unmap(void *mapping)
free(tmap);
}
+static int get_reader(struct trace_mmap *tmap)
+{
+ return ioctl(tmap->fd, TRACE_MMAP_IOCTL_GET_READER);
+}
+
__hidden int trace_mmap_load_subbuf(void *mapping, struct kbuffer *kbuf)
{
struct trace_mmap *tmap = mapping;
@@ -171,11 +176,18 @@ __hidden int trace_mmap_load_subbuf(void *mapping, struct kbuffer *kbuf)
kbuffer_refresh(kbuf);
/* Are there still events to read? */
- if (kbuffer_curr_size(kbuf))
+ if (kbuffer_curr_size(kbuf)) {
+ /* If current is greater than what was read, refresh */
+ if (kbuffer_curr_offset(kbuf) + kbuffer_curr_size(kbuf) >
+ tmap->map->reader.read) {
+ if (get_reader(tmap) < 0)
+ return -1;
+ }
return 1;
+ }
/* See if a new page is ready? */
- if (ioctl(tmap->fd, TRACE_MMAP_IOCTL_GET_READER) < 0)
+ if (get_reader(tmap) < 0)
return -1;
id = tmap->map->reader.id;
data = tmap->data + tmap->map->subbuf_size * id;
--
2.43.0
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