[PATCH v8 00/21] printk: console: Per-console loglevels

[Chris Down <chris@chrisdown.name>]

v8:

- Fully resolve loglevel before printk_delay to aid LOGLEVEL_DEFAULT
- Prioritise user-specified console options over SPCR/DT
- Synchronise console unregistration against atomic flushers in nbcon
- Optimise printk_delay to avoid SRCU walk when no delay set
- Restored accidentally deleted comment in console_srcu_read_flags
- Removed extra put_device() in console unregistration
- Changed open coded console_srcu_read_lock usage to functions
- Removed redundant newcon->classdev = NULL initialisation
- Fixed off-by-one errors in loglevel examples in docs (4 vs >4)
- In docs clarified "messages won't appear" edge case
- In docs, rewrote performance impact section per Petr
- In docs, removed obsolete minimum_console_loglevel section
- Removed redundant newcon->level init in try_enable_preferred_console
- Split up commits some more where reasonable (with tags kept)
- Make SYSLOG_ACTION_CONSOLE_{ON,OFF} only restore IPCL when they did it
- Drop sysrq loglevel overrides, just use ignore_per_console_loglevel
- Set options to NULL if empty so drivers keep baud
- Copy console= option strings before stripping loglevel for mips/jazz
- Initialise consoles with LOGLEVEL_DEFAULT so sysfs never exposes 0
- Clamp sysrq loglevels

v7:

- Disallow writing -1 to the global console_loglevel sysctl
- Change printk_get_next_message() to take effective loglevel
- Update suppress_message_printing() to take effective loglevel
- Use CONSOLE_LOGLEVEL_MOTORMOUTH for devkmsg_read()
- Fix documentation per Petr's review comments
- Add console_srcu_read_loglevel() for lockless reading
- Rename per_console_loglevel_is_set() to has_per_console_loglevel()
- Refactor API to take int con_level for better lockdep checking
- Update callers to read con_level using console_srcu_read_loglevel()
- Remove hierarchy comment since it's obvious from the code
- Use LOGLEVEL_DEFAULT as base level instead of hardcoded -1
- Use pr_warn_once() in sysrq handling instead of manual warned variable
- Split sysrq handling into separate commit
- Update code/ABI documentation to change loglevel bounds from 0 to 1
- Remove 'enabled' attribute from sysfs interface
- Move #ifdefs out of sysfs.c
- Fix console_clamp_loglevel() to use documented bounds
- Initialise classdev and level in try_enable_default_console()
- Fix race condition, use console_list_lock() in console_setup_class()
- Remove NULL check before device_unregister()
- Add data_race() annotations to READ_ONCE/WRITE_ONCE for KCSAN
- Remove pr_warn() for unknown loglevel source
- Add error handling for kzalloc() failure
- Make console_class constant via class_register() per Greg
- Export do_proc_dointvec() and do_proc_dointvec_conv()
- Refactor to use @conv callback approach
- Rename printk_console_loglevel() to proc_dointvec_console_loglevel()
- Simplify level assignment to `newcon->level = c->level;` per Petr
- Add missing loglevel= parameter documentation
- Change printk_sysctl_deprecated to proc_dointvec_printk_deprecated
- Add missing kernel parameter documentation for ignore_loglevel
- Reject KERN_EMERG (0) consistently
- Add comprehensive usage examples to per-console-loglevel.rst
- Add troubleshooting section with common issues and solutions
- Update ABI documentation with error conditions and permissions
- Document new struct console fields (level and classdev)
- Rename clamp_loglevel() to console_clamp_loglevel() for clarity
- Add kernel doc comments for internal API functions where it helps
- Initialise classdev in try_enable_default_console() explicitly
- Mark console devices with device_set_pm_not_required()
- Add syslog_lock around SYSLOG_ACTION_CONSOLE_{OFF,ON}

v6:

- Add .rst suffix to documentation in do_syslog
- Add loglevel table to per-console-loglevel.rst and serial-console.rst
- Add newlines between multiline bullets in per-console-loglevel.rst
- Make effective_loglevel doc more clear
- Remove ignore_per_console_loglevel doc, it's not shown in sysfs now
- Use READ_ONCE/WRITE_ONCE for con->level
- Ignore/restore per console loglevel in sysrq
- Add new fields to comment above struct console
- Remove now unused flags field on console_cmdline
- Remove WARN_ON_ONCE(!con) in effective loglevel checks
- Avoid underflow in find_and_remove_console_option if val_buf_size == 0
- Better error message on oversize in find_and_remove_loglevel_option
- Reject if clamped in find_and_remove_loglevel_option
- Clarify level setting logic in __add_preferred_console
- Move console emission check to printk_delay itself
- Use console_src_read_flags in enabled_show
- Infer if extended from con in printk_get_next_message, don't pass args
- Remove misleading comment about early consoles in console_init
- Use a goto in loglevel_store to avoid setting level in multiple places
- Mention only @flags and @level are valid in printk_get_next_message
- Use LOGLEVEL_DEBUG for max clamp in sysctls
- Update for class_create interface changes
- Move sysctl functionality out to sysfs.c
- Purge default_console_loglevel
- Update sysctl docs for kernel.printk deprecation

v5:

- Fix syntax in boot_delay

v4:

- Change base to Linus' master
- Use SRCU iterators for console walks
- Override per-console loglevels on magic sysrq
- Fix htmldocs
- Fix mistaken __user annotation in sysctl callbacks
- Consistently use indexed names (eg. ttyS0 instead of ttyS)
- Remove "The loglevel for a console can be set in many places" comment
- Remove CON_LOGLEVEL flag and infer based on >0
- Open code our dev_get_drvdata console stashing
- Split out console_effective_loglevel functions per Petr's suggestion
- Make boot_delay_msec/printk_delay check if it would be emitted
- Simplify warning on SYSLOG_ACTION_CONSOLE_LEVEL
- Save/restore ignore_per_console_loglevel on syslog console actions
- Unify min/max level checks across sysfs/proc/syslog
- Add find_and_remove_console_option to avoid affecting io/mmio options

v3:

- Update to work with John's kthread patches
- Remove force_console_loglevel, now we only have global and local levels
- Remove minimum_console_loglevel control and document how to change it
- The minimum loglevel is now only honoured on setting global/local level
- Add ignore_per_console_loglevel
- Return -EINVAL if trying to set below minimum console level
- Add parser for named console= options
- Fix docs around ignore_loglevel: it can be changed at runtime
- Fix ordering in "in order of authority" docs
- Remove duplicated default_console_loglevel doc
- Only warn once on syslog() use

v2:

- Dynamically allocate struct device*
- Document sysfs attributes in Documentation/ABI/
- Use sysfs_emit() instead of sprintf() in dev sysfs files
- Remove WARN_ON() for device_add/IS_ERR(console_class)
- Remove "soon" comment for kernel.printk
- Fix !CONFIG_PRINTK build
- Fix device_unregister() NULL dereference if called before class setup
- Add new documentation to MAINTAINERS

Chris Down (21):
  printk: Fully resolve loglevel before deciding printk delay
    suppression
  printk: Avoid spuriously delaying messages not solicited by any
    console
  printk: Prioritise user-specified configuration over SPCR/DT
  printk: Use effective loglevel for suppression and extended console
    state
  printk: console: Add per-console loglevel support to struct console
  printk: nbcon: Synchronise console unregistration against atomic
    flushers
  printk: Introduce per-console loglevel support
  printk: Iterate registered consoles for delay suppression decisions
  printk: Optimise printk_delay() to avoid walking consoles under SRCU
  printk: Add synchronisation for concurrent console state changes
  printk: Add ignore_per_console_loglevel module parameter
  printk: Ensure sysrq output bypasses per-console filtering
  printk: Toggle ignore_per_console_loglevel via syslog
  printk: console: Introduce sysfs interface for per-console loglevels
  printk: sysrq: Clamp console loglevel to valid range
  printk: Constrain hardware-addressed console checks to name position
  printk: Support setting initial console loglevel via console= on
    cmdline
  printk: Deconstruct kernel.printk into discrete sysctl controls
  printk: docs: Add comprehensive guidance for per-console loglevels
  printk: Deprecate the kernel.printk sysctl interface
  printk: Purge default_console_loglevel

 Documentation/ABI/testing/sysfs-class-console |  58 +++
 Documentation/admin-guide/index.rst           |   1 +
 .../admin-guide/kernel-parameters.txt         |  31 +-
 .../admin-guide/per-console-loglevel.rst      | 252 +++++++++
 Documentation/admin-guide/serial-console.rst  |  37 +-
 Documentation/admin-guide/sysctl/kernel.rst   |  25 +-
 Documentation/core-api/printk-basics.rst      |  35 +-
 Documentation/networking/netconsole.rst       |  16 +
 MAINTAINERS                                   |   2 +
 drivers/tty/sysrq.c                           |   8 +-
 include/linux/console.h                       |  40 ++
 include/linux/printk.h                        |   4 +-
 include/linux/sysctl.h                        |   7 +
 kernel/printk/Makefile                        |   2 +-
 kernel/printk/console_cmdline.h               |   1 +
 kernel/printk/internal.h                      |  20 +-
 kernel/printk/nbcon.c                         |  34 +-
 kernel/printk/printk.c                        | 489 ++++++++++++++++--
 kernel/printk/sysctl.c                        |  77 ++-
 kernel/printk/sysfs.c                         | 290 +++++++++++
 kernel/sysctl.c                               |  18 +-
 21 files changed, 1362 insertions(+), 85 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-class-console
 create mode 100644 Documentation/admin-guide/per-console-loglevel.rst
 create mode 100644 kernel/printk/sysfs.c


base-commit: a9f349e3c0bebe7ae97750b32a72f452bdf707e2
-- 
2.51.2