path: root/Documentation
diff options
authorLinus Torvalds <torvalds@linux-foundation.org>2020-02-26 10:34:42 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-02-26 10:34:42 -0800
commit91ad64a84e9e63e2906ae714dfa3933dd3f64c64 (patch)
treea6751cdf19320e5e5a4cd0ab876de5f1146a1d0e /Documentation
parentMerge tag 'linux-kselftest-kunit-5.6-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest (diff)
parentbootconfig: Fix CONFIG_BOOTTIME_TRACING dependency issue (diff)
Merge tag 'trace-v5.6-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
Pull tracing and bootconfig updates: "Fixes and changes to bootconfig before it goes live in a release. Change in API of bootconfig (before it comes live in a release): - Have a magic value "BOOTCONFIG" in initrd to know a bootconfig exists - Set CONFIG_BOOT_CONFIG to 'n' by default - Show error if "bootconfig" on cmdline but not compiled in - Prevent redefining the same value - Have a way to append values - Added a SELECT BLK_DEV_INITRD to fix a build failure Synthetic event fixes: - Switch to raw_smp_processor_id() for recording CPU value in preempt section. (No care for what the value actually is) - Fix samples always recording u64 values - Fix endianess - Check number of values matches number of fields - Fix a printing bug Fix of trace_printk() breaking postponed start up tests Make a function static that is only used in a single file" * tag 'trace-v5.6-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: bootconfig: Fix CONFIG_BOOTTIME_TRACING dependency issue bootconfig: Add append value operator support bootconfig: Prohibit re-defining value on same key bootconfig: Print array as multiple commands for legacy command line bootconfig: Reject subkey and value on same parent key tools/bootconfig: Remove unneeded error message silencer bootconfig: Add bootconfig magic word for indicating bootconfig explicitly bootconfig: Set CONFIG_BOOT_CONFIG=n by default tracing: Clear trace_state when starting trace bootconfig: Mark boot_config_checksum() static tracing: Disable trace_printk() on post poned tests tracing: Have synthetic event test use raw_smp_processor_id() tracing: Fix number printing bug in print_synth_event() tracing: Check that number of vals matches number of synth event fields tracing: Make synth_event trace functions endian-correct tracing: Make sure synth_event_trace() example always uses u64
Diffstat (limited to 'Documentation')
1 files changed, 31 insertions, 3 deletions
diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst
index b342a6796392..cf2edcd09183 100644
--- a/Documentation/admin-guide/bootconfig.rst
+++ b/Documentation/admin-guide/bootconfig.rst
@@ -62,6 +62,30 @@ Or more shorter, written as following::
In both styles, same key words are automatically merged when parsing it
at boot time. So you can append similar trees or key-values.
+Same-key Values
+It is prohibited that two or more values or arrays share a same-key.
+For example,::
+ foo = bar, baz
+ foo = qux # !ERROR! we can not re-define same key
+If you want to append the value to existing key as an array member,
+you can use ``+=`` operator. For example::
+ foo = bar, baz
+ foo += qux
+In this case, the key ``foo`` has ``bar``, ``baz`` and ``qux``.
+However, a sub-key and a value can not co-exist under a parent key.
+For example, following config is NOT allowed.::
+ foo = value1
+ foo.bar = value2 # !ERROR! subkey "bar" and value "value1" can NOT co-exist
@@ -102,9 +126,13 @@ Boot Kernel With a Boot Config
Since the boot configuration file is loaded with initrd, it will be added
-to the end of the initrd (initramfs) image file. The Linux kernel decodes
-the last part of the initrd image in memory to get the boot configuration
+to the end of the initrd (initramfs) image file with size, checksum and
+12-byte magic word as below.
+The Linux kernel decodes the last part of the initrd image in memory to
+get the boot configuration data.
Because of this "piggyback" method, there is no need to change or
update the boot loader and the kernel image itself.