Hi,

Here is the v8 of the series to improve backup instances of
the persistent ring buffer. The previous version is here:

https://lore.kernel.org/all/177062912135.1230888.17419570791737357433.stgit@mhiramat.tok.corp.google.com/

In this version, I modified the tracefs to check the file permission
even if the user has CAP_DAC_OVERRIDE as same as sysfs[3/6] and remove
read-only check from each read() operations[4/6]. Also add a bugfix [2/6]
for per-cpu buffer_size_kb permission.

Series Description
------------------
Since backup instances are a kind of snapshot of the persistent
ring buffer, it should be readonly. And if it is readonly
there is no reason to keep it after reading all data via trace_pipe
because the data has been consumed. But user should be able to remove
the readonly instance by rmdir or truncating `trace` file.

Thus, [3/5] makes backup instances readonly (not able to write any
events, cleanup trace, change buffer size). Also, [4/5] removes the
backup instance after consuming all data via trace_pipe.
With this improvements, even if we makes a backup instance (using
the same amount of memory of the persistent ring buffer), it will
be removed after reading the data automatically.

---

Masami Hiramatsu (Google) (6):
      tracing: Fix to set write permission to per-cpu buffer_size_kb
      tracing: Reset last_boot_info if ring buffer is reset
      tracefs: Check file permission even if user has CAP_DAC_OVERRIDE
      tracing: Make the backup instance non-reusable
      tracing: Remove the backup instance automatically after read
      tracing/Documentation: Add a section about backup instance


 Documentation/trace/debugging.rst |   19 +++++
 fs/tracefs/event_inode.c          |    2 +
 fs/tracefs/inode.c                |   36 +++++++++-
 fs/tracefs/internal.h             |    3 +
 kernel/trace/trace.c              |  140 ++++++++++++++++++++++++++++---------
 kernel/trace/trace.h              |   13 +++
 kernel/trace/trace_boot.c         |    5 +
 kernel/trace/trace_events.c       |   76 ++++++++++++--------
 8 files changed, 224 insertions(+), 70 deletions(-)

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>