[PATCH v4 00/18] tracing/remotes: Add printk, dump_on_panic and boot parameters

[Vincent Donnefort <vdonnefort@google.com>]

This series extends the recently introduced trace remotes
infrastructure, bringing useful features for developers:

  * dump_on_panic: Dump the trace remote buffer on system panic.
  * dmesg: Redirect remote events to dmesg.
  * trace_remote=: Configure a trace_remote from the commandline.
  * poll_ms: Modify the polling period.

It also brings a couple of optimisations:

  * In-header compressed length support for small events.
  * Single work thread for remote polling.

And some misc improvements:

  * Use kstrtobool where possible
  * Free resources on remote registration failure

Changelog:

v4:

  * Rebase on 7.2-rc6
  * Use trace_append_boot_param() to parse cmdline options.
  * Fix trace_remote_iterator cleanup order for non-consuming iterators
    (Sashiko).

v3 (https://lore.kernel.org/all/20260721103603.342266-1-vdonnefort@google.com/):

  * Make sure dmesg and panic handlers are using null-terminated
    trace_seq.
  * Make struct trace_remote more compact
  * Fix dump_on_panic test unloaded case (Sashiko)
  * Rebase on 7.2-rc4

v2 (https://lore.kernel.org/all/20260605163825.1762953-1-vdonnefort@google.com/):

Sashiko had a few spot-on comments on the v1 which forced me to heavily
re-arrange the series, so I thought it'd be alright to send a v2
already including those changes.

  * dump_on_oops -> dump_on_panic
  * printk -> dmesg
  * Allow to configure poll_ms
  * Make the ring_buffer_iter functions panic-friendly
  * Gate tracefs .open on remote registration (Sashiko)
  * Use irqsave for reader lock (Sashiko)
  * Fix iter locking for TRI_DMESG (Sashiko)
  * Yield in the dmesg work (Sashiko)

v1 (https://lore.kernel.org/all/20260602171146.2238998-1-vdonnefort@google.com/)

Vincent Donnefort (18):
  tracing/remotes: Gate tracefs files opening on trace remote
    registration
  tracing/remotes: Release tracefs,eventfs on registration failure
  tracing/remotes: Use kstrtobool for boolean tracefs files
  tracing/remotes: Use a single per-remote polling work
  tracing/simple_ring_buffer: Add support for compressed length
  tracing/remotes: Add dmesg tracefs file
  tracing/remotes: selftests: Add a test for the dmesg tracefs file
  tracing/remotes: selftests: Prefix hypervisor folder
  ring-buffer: Use irqsave for the reader lock in
    ring_buffer_poll_remote
  ring-buffer: Use panic-friendly locking in ring_buffer_iter interface
  ring-buffer: Add ring_buffer_read_remote_meta_page()
  ring-buffer: Add kerneldoc for ring_buffer_poll_remote
  tracing/remotes: Add dump_on_panic tracefs file
  tracing/remotes: selftests: Add a test for the dump_on_panic tracefs
    file
  tracing/remotes: Add poll_ms tracefs file
  tracing/remotes: Add trace_remote cmdline options
  Documentation: tracing/remotes: Add detailed tracefs layout
  Documentation/kernel-parameters: Add trace_remote

 .../admin-guide/kernel-parameters.txt         |  19 +
 Documentation/trace/remotes.rst               |  66 +-
 include/linux/ring_buffer.h                   |   1 +
 kernel/trace/ring_buffer.c                    |  88 +-
 kernel/trace/simple_ring_buffer.c             |  25 +-
 kernel/trace/trace_remote.c                   | 818 +++++++++++++++---
 .../buffer_size.tc                            |   0
 .../test.d/remotes/00hypervisor/dmesg.tc      |  11 +
 .../remotes/00hypervisor/dump_on_panic.tc     |  11 +
 .../{hypervisor => 00hypervisor}/hotplug.tc   |   0
 .../{hypervisor => 00hypervisor}/reset.tc     |   0
 .../{hypervisor => 00hypervisor}/trace.tc     |   0
 .../trace_pipe.tc                             |   0
 .../{hypervisor => 00hypervisor}/unloading.tc |   0
 .../selftests/ftrace/test.d/remotes/dmesg.tc  |  72 ++
 .../ftrace/test.d/remotes/dump_on_panic.tc    |  51 ++
 .../selftests/ftrace/test.d/remotes/functions |   2 +
 17 files changed, 1024 insertions(+), 140 deletions(-)
 rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/buffer_size.tc (100%)
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/dmesg.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/00hypervisor/dump_on_panic.tc
 rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/hotplug.tc (100%)
 rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/reset.tc (100%)
 rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/trace.tc (100%)
 rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/trace_pipe.tc (100%)
 rename tools/testing/selftests/ftrace/test.d/remotes/{hypervisor => 00hypervisor}/unloading.tc (100%)
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/dmesg.tc
 create mode 100644 tools/testing/selftests/ftrace/test.d/remotes/dump_on_panic.tc


base-commit: 075b74841bd0065a3bda3440873c747938e69b68
-- 
2.55.0.571.g244d577d93-goog