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| author | Vincent Donnefort <vdonnefort@google.com> | 2024-05-10 17:04:32 +0300 |
|---|---|---|
| committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2024-05-14 01:09:56 +0300 |
| commit | cf9f0f7c4c5bb45e7bb270e48bab6f7837825a64 (patch) | |
| tree | 74d4eeab2c64aea8a583cbec5cb12145cf9bccbd /include/uapi | |
| parent | 117c39200d9d760cbd5944bb89efb7b9c51965aa (diff) | |
| download | linux-cf9f0f7c4c5bb45e7bb270e48bab6f7837825a64.tar.xz | |
tracing: Allow user-space mapping of the ring-buffer
Currently, user-space extracts data from the ring-buffer via splice,
which is handy for storage or network sharing. However, due to splice
limitations, it is imposible to do real-time analysis without a copy.
A solution for that problem is to let the user-space map the ring-buffer
directly.
The mapping is exposed via the per-CPU file trace_pipe_raw. The first
element of the mapping is the meta-page. It is followed by each
subbuffer constituting the ring-buffer, ordered by their unique page ID:
* Meta-page -- include/uapi/linux/trace_mmap.h for a description
* Subbuf ID 0
* Subbuf ID 1
...
It is therefore easy to translate a subbuf ID into an offset in the
mapping:
reader_id = meta->reader->id;
reader_offset = meta->meta_page_size + reader_id * meta->subbuf_size;
When new data is available, the mapper must call a newly introduced ioctl:
TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to
point to the next reader containing unread data.
Mapping will prevent snapshot and buffer size modifications.
Link: https://lore.kernel.org/linux-trace-kernel/20240510140435.3550353-4-vdonnefort@google.com
CC: <linux-mm@kvack.org>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Diffstat (limited to 'include/uapi')
| -rw-r--r-- | include/uapi/linux/trace_mmap.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/include/uapi/linux/trace_mmap.h b/include/uapi/linux/trace_mmap.h index b682e9925539..bd1066754220 100644 --- a/include/uapi/linux/trace_mmap.h +++ b/include/uapi/linux/trace_mmap.h @@ -43,4 +43,6 @@ struct trace_buffer_meta { __u64 Reserved2; }; +#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1) + #endif /* _TRACE_MMAP_H_ */ |