Currently, the actual perf ring buffer is one page into the mmap area,
following the user page and the userspace follows this convention. This
patch adds data_{offset,size} fields to user_page that can be used by
userspace instead for locating perf data in the mmap area.
Right now, it is made to follow the existing convention that
data_offset == PAGE_SIZE and
data_offset + data_size == mmap_size.
Signed-off-by: Alexander Shishkin <alexander.shish...@linux.intel.com>
---
include/uapi/linux/perf_event.h | 5 +++++
kernel/events/core.c | 2 ++
2 files changed, 7 insertions(+)
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 853bc1c..ef95af4 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -488,9 +488,14 @@ struct perf_event_mmap_page {
* In this case the kernel will not over-write unread data.
*
* See perf_output_put_handle() for the data ordering.
+ *
+ * data_{offset,size} indicate the location and size of the perf record
+ * buffer within the mmapped area.
*/
__u64 data_head; /* head in the data section */
__u64 data_tail; /* user-space written tail */
+ __u64 data_offset; /* where the buffer starts */
+ __u64 data_size; /* data buffer size */
};
#define PERF_RECORD_MISC_CPUMODE_MASK (7 << 0)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0b9309b..bbe8b48 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3768,6 +3768,8 @@ static void perf_event_init_userpage(struct perf_event
*event)
/* Allow new userspace to detect that bit 0 is deprecated */
userpg->cap_bit0_is_deprecated = 1;
userpg->size = offsetof(struct perf_event_mmap_page, __reserved);
+ userpg->data_offset = PAGE_SIZE;
+ userpg->data_size = perf_data_size(rb);
unlock:
rcu_read_unlock();
--
2.0.0.rc2
--
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