Logging

The logging API provides a common interface to process messages issued by developers. Messages are passed through a frontend and are then processed by active backends. Custom frontend and backends can be used if needed.

Summary of the logging features:

Deferred logging reduces the time needed to log a message by shifting time consuming operations to a known context instead of processing and sending the log message when called.
Multiple backends supported (up to 9 backends).
Custom frontend support. It can work together with backends.
Compile time filtering on module level.
Run time filtering independent for each backend.
Additional run time filtering on module instance level.
Timestamping with user provided function. Timestamp can have 32 or 64 bits.
Dedicated API for dumping data.
Dedicated API for handling transient strings.
Panic support - in panic mode logging switches to blocking, synchronous processing.
Printk support - printk message can be redirected to the logging.
Design ready for multi-domain/multi-processor system.
Support for logging floating point variables and long long arguments.
Built-in copying of transient strings used as arguments.
Support for multi-domain logging.

Logging API is highly configurable at compile time as well as at run time. Using Kconfig options (see Global Kconfig Options) logs can be gradually removed from compilation to reduce image size and execution time when logs are not needed. During compilation logs can be filtered out on module basis and severity level.

Logs can also be compiled in but filtered on run time using dedicate API. Run time filtering is independent for each backend and each source of log messages. Source of log messages can be a module or specific instance of the module.

There are four severity levels available in the system: error, warning, info and debug. For each severity level the logging API (include/zephyr/logging/log.h) has set of dedicated macros. Logger API also has macros for logging data.

For each level following set of macros are available:

LOG_X for standard printf-like messages, e.g. LOG_ERR.
LOG_HEXDUMP_X for dumping data, e.g. LOG_HEXDUMP_WRN.
LOG_INST_X for standard printf-like message associated with the particular instance, e.g. LOG_INST_INF.
LOG_INST_HEXDUMP_X for dumping data associated with the particular instance, e.g. LOG_HEXDUMP_INST_DBG

There are two configuration categories: configurations per module and global configuration. When logging is enabled globally, it works for modules. However, modules can disable logging locally. Every module can specify its own logging level. The module must define the LOG_LEVEL macro before using the API. Unless a global override is set, the module logging level will be honored. The global override can only increase the logging level. It cannot be used to lower module logging levels that were previously set higher. It is also possible to globally limit logs by providing maximal severity level present in the system, where maximal means lowest severity (e.g. if maximal level in the system is set to info, it means that errors, warnings and info levels are present but debug messages are excluded).

Each module which is using the logging must specify its unique name and register itself to the logging. If module consists of more than one file, registration is performed in one file but each file must define a module name.

Logger’s default frontend is designed to be thread safe and minimizes time needed to log the message. Time consuming operations like string formatting or access to the transport are not performed by default when logging API is called. When logging API is called a message is created and added to the list. Dedicated, configurable buffer for pool of log messages is used. There are 2 types of messages: standard and hexdump. Each message contain source ID (module or instance ID and domain ID which might be used for multiprocessor systems), timestamp and severity level. Standard message contains pointer to the string and arguments. Hexdump message contains copied data and string.

Global Kconfig Options 

These options can be found in the following path subsys/logging/Kconfig.

CONFIG_LOG: Global switch, turns on/off the logging.

Mode of operations:

CONFIG_LOG_MODE_DEFERRED: Deferred mode.

CONFIG_LOG_MODE_IMMEDIATE: Immediate (synchronous) mode.

CONFIG_LOG_MODE_MINIMAL: Minimal footprint mode.

Filtering options:

CONFIG_LOG_RUNTIME_FILTERING: Enables runtime reconfiguration of the filtering.

CONFIG_LOG_DEFAULT_LEVEL: Default level, sets the logging level used by modules that are not setting their own logging level.

CONFIG_LOG_OVERRIDE_LEVEL: It overrides module logging level when it is not set or set lower than the override value.

CONFIG_LOG_MAX_LEVEL: Maximal (lowest severity) level which is compiled in.

Processing options:

CONFIG_LOG_MODE_OVERFLOW: When new message cannot be allocated, oldest one are discarded.

CONFIG_LOG_BLOCK_IN_THREAD: If enabled and new log message cannot be allocated thread context will block for up to CONFIG_LOG_BLOCK_IN_THREAD_TIMEOUT_MS or until log message is allocated.

CONFIG_LOG_PRINTK: Redirect printk calls to the logging.

CONFIG_LOG_PROCESS_TRIGGER_THRESHOLD: When number of buffered log messages reaches the threshold dedicated thread (see log_thread_set()) is waken up. If CONFIG_LOG_PROCESS_THREAD is enabled then this threshold is used by the internal thread.

CONFIG_LOG_PROCESS_THREAD: When enabled, logging thread is created which handles log processing.

CONFIG_LOG_PROCESS_THREAD_STARTUP_DELAY_MS: Delay in milliseconds after which logging thread is started.

CONFIG_LOG_BUFFER_SIZE: Number of bytes dedicated for the circular packet buffer.

CONFIG_LOG_FRONTEND: Direct logs to a custom frontend.

CONFIG_LOG_FRONTEND_ONLY: No backends are used when messages goes to frontend.

CONFIG_LOG_CUSTOM_HEADER: Injects an application provided header into log.h

CONFIG_LOG_TIMESTAMP_64BIT: 64 bit timestamp.

Formatting options:

CONFIG_LOG_FUNC_NAME_PREFIX_ERR: Prepend standard ERROR log messages with function name. Hexdump messages are not prepended.

CONFIG_LOG_FUNC_NAME_PREFIX_WRN: Prepend standard WARNING log messages with function name. Hexdump messages are not prepended.

CONFIG_LOG_FUNC_NAME_PREFIX_INF: Prepend standard INFO log messages with function name. Hexdump messages are not prepended.

CONFIG_LOG_FUNC_NAME_PREFIX_DBG: Prepend standard DEBUG log messages with function name. Hexdump messages are not prepended.

CONFIG_LOG_BACKEND_SHOW_COLOR: Enables coloring of errors (red) and warnings (yellow).

CONFIG_LOG_BACKEND_FORMAT_TIMESTAMP: If enabled timestamp is formatted to hh:mm:ss:mmm,uuu. Otherwise is printed in raw format.

Backend options:

CONFIG_LOG_BACKEND_UART: Enabled built-in UART backend.

Usage 

Logging in a module 

In order to use logging in the module, a unique name of a module must be specified and module must be registered using LOG_MODULE_REGISTER. Optionally, a compile time log level for the module can be specified as the second parameter. Default log level (CONFIG_LOG_DEFAULT_LEVEL) is used if custom log level is not provided.

#include <zephyr/logging/log.h>
LOG_MODULE_REGISTER(foo, CONFIG_FOO_LOG_LEVEL);

If the module consists of multiple files, then LOG_MODULE_REGISTER() should appear in exactly one of them. Each other file should use LOG_MODULE_DECLARE to declare its membership in the module. Optionally, a compile time log level for the module can be specified as the second parameter. Default log level (CONFIG_LOG_DEFAULT_LEVEL) is used if custom log level is not provided.

#include <zephyr/logging/log.h>
/* In all files comprising the module but one */
LOG_MODULE_DECLARE(foo, CONFIG_FOO_LOG_LEVEL);

In order to use logging API in a function implemented in a header file LOG_MODULE_DECLARE macro must be used in the function body before logging API is called. Optionally, a compile time log level for the module can be specified as the second parameter. Default log level (CONFIG_LOG_DEFAULT_LEVEL) is used if custom log level is not provided.

#include <zephyr/logging/log.h>

static inline void foo(void)
{
     LOG_MODULE_DECLARE(foo, CONFIG_FOO_LOG_LEVEL);

     LOG_INF("foo");
}

Dedicated Kconfig template (subsys/logging/Kconfig.template.log_config) can be used to create local log level configuration.

Example below presents usage of the template. As a result CONFIG_FOO_LOG_LEVEL will be generated:

module = FOO
module-str = foo
source "subsys/logging/Kconfig.template.log_config"

Logging in a module instance 

In case of modules which are multi-instance and instances are widely used across the system enabling logs will lead to flooding. Logger provide the tools which can be used to provide filtering on instance level rather than module level. In that case logging can be enabled for particular instance.

In order to use instance level filtering following steps must be performed:

a pointer to specific logging structure is declared in instance structure. LOG_INSTANCE_PTR_DECLARE is used for that.

#include <zephyr/logging/log_instance.h>

struct foo_object {
     LOG_INSTANCE_PTR_DECLARE(log);
     uint32_t id;
}

module must provide macro for instantiation. In that macro, logging instance is registered and log instance pointer is initialized in the object structure.

#define FOO_OBJECT_DEFINE(_name)                             \
     LOG_INSTANCE_REGISTER(foo, _name, CONFIG_FOO_LOG_LEVEL) \
     struct foo_object _name = {                             \
             LOG_INSTANCE_PTR_INIT(log, foo, _name)          \
     }

Note that when logging is disabled logging instance and pointer to that instance are not created.

In order to use the instance logging API in a source file, a compile-time log level must be set using LOG_LEVEL_SET.

LOG_LEVEL_SET(CONFIG_FOO_LOG_LEVEL);

void foo_init(foo_object *f)
{
     LOG_INST_INF(f->log, "Initialized.");
}

In order to use the instance logging API in a header file, a compile-time log level must be set using LOG_LEVEL_SET.

static inline void foo_init(foo_object *f)
{
     LOG_LEVEL_SET(CONFIG_FOO_LOG_LEVEL);

     LOG_INST_INF(f->log, "Initialized.");
}

Controlling the logging 

By default, logging processing in deferred mode is handled internally by the dedicated task which starts automatically. However, it might not be available if multithreading is disabled. It can also be disabled by unsetting CONFIG_LOG_PROCESS_TRIGGER_THRESHOLD. In that case, logging can be controlled using API defined in include/zephyr/logging/log_ctrl.h. Logging must be initialized before it can be used. Optionally, user can provide function which returns timestamp value. If not provided, k_cycle_get or k_cycle_get_32 is used for timestamping. log_process() function is used to trigger processing of one log message (if pending). Function returns true if there is more messages pending. However, it is recommended to use macro wrappers (LOG_INIT and LOG_PROCESS) which handles case when logging is disabled.

Following snippet shows how logging can be processed in simple forever loop.

#include <zephyr/log_ctrl.h>

int main(void)
{
     LOG_INIT();
     /* If multithreading is enabled provide thread id to the logging. */
     log_thread_set(k_current_get());

     while (1) {
             if (LOG_PROCESS() == false) {
                     /* sleep */
             }
     }
}

If logs are processed from a thread (user or internal) then it is possible to enable a feature which will wake up processing thread when certain amount of log messages are buffered (see CONFIG_LOG_PROCESS_TRIGGER_THRESHOLD).

Logging panic 

In case of error condition system usually can no longer rely on scheduler or interrupts. In that situation deferred log message processing is not an option. Logger controlling API provides a function for entering into panic mode (log_panic()) which should be called in such situation.

When log_panic() is called, _panic_ notification is sent to all active backends. Once all backends are notified, all buffered messages are flushed. Since that moment all logs are processed in a blocking way.

Printk 

Typically, logging and printk() is using the same output for which they compete. This can lead to issues if the output does not support preemption but also it may result in the corrupted output because logging data is interleaved with printk data. However, it is possible to redirect printk messages to the logging subsystem by enabling CONFIG_LOG_PRINTK. In that case, printk entries are treated as log messages with level 0 (they cannot be disabled). When enabled, logging manages the output so there is no interleaving. However, in the deferred mode it changes the behavior of the printk because output is delayed until logging thread processes the data. CONFIG_LOG_PRINTK is by default enabled.

Architecture 

Logging consists of 3 main parts:

Frontend
Core
Backends

Log message is generated by a source of logging which can be a module or instance of a module.

Default Frontend 

Default frontend is engaged when logging API is called in a source of logging (e.g. LOG_INF) and is responsible for filtering a message (compile and run time), allocating buffer for the message, creating the message and committing that message. Since logging API can be called in an interrupt, frontend is optimized to log the message as fast as possible.

Log message

Log message contains message descriptor (source, domain and level), timestamp, formatted string details (see Cbprintf Packaging) and optional data. Log messages are stored in a continuous block of memory. Memory is allocated from a circular packet buffer (Multi Producer Single Consumer Packet Buffer). It has few consequences:

Each message is self-contained, continuous block of memory thus it is suited for copying the message (e.g. for offline processing).

Messages must be sequentially freed. Backend processing is synchronous. Backend can make a copy for deferred processing.

Log message has following format:

Message Header	2 bits: MPSC packet buffer header
	1 bit: Trace/Log message flag
	3 bits: Domain ID
	3 bits: Level
	10 bits: Cbprintf Package Length
	12 bits: Data length
	1 bit: Reserved
	pointer: Pointer to the source descriptor [1]
	32 or 64 bits: Timestamp [1]
	Optional padding [2]
Cbprintf package (optional)	Header
	Arguments
	Appended strings
Hexdump data (optional)
Alignment padding (optional)

Footnotes

Log message allocation

It may happen that frontend cannot allocate a message. It happens if system is generating more log messages than it can process in certain time frame. There are two strategies to handle that case:

No overflow - new log is dropped if space for a message cannot be allocated.
Overflow - oldest pending messages are freed, until new message can be allocated. Enabled by CONFIG_LOG_MODE_OVERFLOW. Note that it degrades performance thus it is recommended to adjust buffer size and amount of enabled logs to limit dropping.

Run-time filtering

If run-time filtering is enabled, then for each source of logging a filter structure in RAM is declared. Such filter is using 32 bits divided into ten 3 bit slots. Except slot 0, each slot stores current filter for one backend in the system. Slot 0 (bits 0-2) is used to aggregate maximal filter setting for given source of logging. Aggregate slot determines if log message is created for given entry since it indicates if there is at least one backend expecting that log entry. Backend slots are examined when message is processed by the core to determine if message is accepted by the given backend. Contrary to compile time filtering, binary footprint is increased because logs are compiled in.

In the example below backend 1 is set to receive errors (slot 1) and backend 2 up to info level (slot 2). Slots 3-9 are not used. Aggregated filter (slot 0) is set to info level and up to this level message from that particular source will be buffered.

slot 0	slot 1	slot 2	slot 3	…	slot 9
INF	ERR	INF	OFF	…	OFF

Custom Frontend 

Custom frontend is enabled using CONFIG_LOG_FRONTEND. Logs are directed to functions declared in include/zephyr/logging/log_frontend.h. If option CONFIG_LOG_FRONTEND_ONLY is enabled then log message is not created and no backend is handled. Otherwise, custom frontend can coexist with backends.

In some cases, logs need to be redirected at the macro level. For these cases, CONFIG_LOG_CUSTOM_HEADER can be used to inject an application provided header named zephyr_custom_log.h at the end of include/zephyr/logging/log.h.

Logging strings 

String arguments are handled by Cbprintf Packaging. See Limitations and recommendations for limitations and recommendations.

Multi-domain support 

More complex systems can consist of multiple domains where each domain is an independent binary. Examples of domains are a core in a multicore SoC or one of the binaries (Secure or Nonsecure) on an ARM TrustZone core.

Tracing and debugging on a multi-domain system is more complex and requires an efficient logging system. Two approaches can be used to structure this logging system:

Log inside each domain independently. This option is not always possible as it requires that each domain has an available backend (for example, UART). This approach can also be troublesome to use and not scalable, as logs are presented on independent outputs.
Use a multi-domain logging system where log messages from each domain end up in one root domain, where they are processed exactly as in a single domain case. In this approach, log messages are passed between domains using a connection between domains created from the backend on one side and linked to the other.

The Log link is an interface introduced in this multi-domain approach. The Log link is responsible for receiving any log message from another domain, creating a copy, and putting that local log message copy (including remote data) into the message queue. This specific log link implementation matches the complementary backend implementation to allow log messages exchange and logger control like configuring filtering, getting log source names, and so on.

There are three types of domains in a multi-domain system:

The end domain has the logging core implementation and a cross-domain backend. It can also have other backends in parallel.
The relay domain has one or more links to other domains but does not have backends that output logs to the user. It has a cross-domain backend either to another relay or to the root domain.
The root domain has one or multiple links and a backend that outputs logs to the user.

See the following image for an example of a multi-domain setup:

../../_images/multidomain.png — Multi-domain example

In this architecture, a link can handle multiple domains. For example, let’s consider an SoC with two ARM Cortex-M33 cores with TrustZone: cores A and B (see the example illustrated above). There are four domains in the system, as each core has both a Secure and a Nonsecure domain. If core A nonsecure (A_NS) is the root domain, it has two links: one to core A secure (A_NS-A_S) and one to core B nonsecure (A_NS-B_NS). B_NS domain has one link, to core B secure B_NS-B_S), and a backend to A_NS.

Since in all instances there is a standard logging subsystem, it is always possible to have multiple backends and simultaneously output messages to them. An example of this is shown in the illustration above as a dotted UART backend on the B_NS domain.

Domain ID

The source of each log message can be identified by the following fields in the header: source_id and domain_id.

The value assigned to the domain_id is relative. Whenever a domain creates a log message, it sets its domain_id to 0. When a message crosses the domain, domain_id changes as it is increased by the link offset. The link offset is assigned during the initialization, where the logger core is iterating over all the registered links and assigned offsets.

The first link has the offset set to 1. The following offset equals the previous link offset plus the number of domains in the previous link.

The following example is shown below, where the assigned domain_ids are shown for each domain:

../../_images/domain_ids.png — Domain IDs assigning example

Let’s consider a log message created on the B_S domain:

Initially, it has its domain_id set to 0.
When the B_NS-B_S link receives the message, it increases the domain_id to 1 by adding the B_NS-B_S offset.
The message is passed to A_NS.
When the A_NS-B_NS link receives the message, it adds the offset (2) to the domain_id. The message ends up with the domain_id set to 3, which uniquely identifies the message originator.

Cross-domain log message

In most cases, the address space of each domain is unique, and one domain cannot access directly the data in another domain. For this reason, the backend can partially process the message before it is passed to another domain. Partial processing can include converting a string package to a fully self-contained version (copying read-only strings to the package body).

Each domain can have a different timestamp source in terms of frequency and offset. Logging does not perform any timestamp conversion.

Runtime filtering

In the single-domain case, each log source has a dedicated variable with runtime filtering for each backend in the system. In the multi-domain case, the originator of the log message is not aware of the number of backends in the root domain.

As such, to filter logs in multiple domains, each source requires a runtime filtering setting in each domain on the way to the root domain. As the number of sources in other domains is not known during the compilation, the runtime filtering of remote sources must use dynamically allocated memory (one word per source). When a backend in the root domain changes the filtering of the module from a remote domain, the local filter is updated. After the update, the aggregated filter (the maximum from all the local backends) is checked and, if changed, the remote domain is informed about this change. With this approach, the runtime filtering works identically in both multi-domain and single-domain scenarios.

Message ordering

Logging does not provide any mechanism for synchronizing timestamps across multiple domains:

If domains have different timestamp sources, messages will be processed in the order of arrival to the buffer in the root domain.
If domains have the same timestamp source or if there is an out-of-bound mechanism that recalculates timestamps, there are 2 options:
- Messages are processed as they arrive in the buffer in the root domain. Messages are unordered but they can be sorted by the host as the timestamp indicates the time of the message generation.
- Links have dedicated buffers. During processing, the head of each buffer is checked and the oldest message is processed first.
  
  With this approach, it is possible to maintain the order of the messages at the cost of a suboptimal memory utilization (since the buffer is not shared) and increased processing latency (see CONFIG_LOG_PROCESSING_LATENCY_US).

Logging backends 

Logging backends are registered using LOG_BACKEND_DEFINE. The macro creates an instance in the dedicated memory section. Backends can be dynamically enabled (log_backend_enable()) and disabled. When Run-time filtering is enabled, log_filter_set() can be used to dynamically change filtering of a module logs for given backend. Module is identified by source ID and domain ID. Source ID can be retrieved if source name is known by iterating through all registered sources.

Logging supports up to 9 concurrent backends. Log message is passed to the each backend in processing phase. Additionally, backend is notified when logging enter panic mode with log_backend_panic(). On that call backend should switch to synchronous, interrupt-less operation or shut down itself if that is not supported. Occasionally, logging may inform backend about number of dropped messages with log_backend_dropped(). Message processing API is version specific.

log_backend_msg2_process() is used for processing message. It is common for standard and hexdump messages because log message hold string with arguments and data. It is also common for deferred and immediate logging.

Message formatting

Logging provides set of function that can be used by the backend to format a message. Helper functions are available in include/zephyr/logging/log_output.h.

Example message formatted using log_output_msg2_process().

[00:00:00.000,274] <info> sample_instance.inst1: logging message

Dictionary-based Logging 

Dictionary-based logging, instead of human readable texts, outputs the log messages in binary format. This binary format encodes arguments to formatted strings in their native storage formats which can be more compact than their text equivalents. For statically defined strings (including the format strings and any string arguments), references to the ELF file are encoded instead of the whole strings. A dictionary created at build time contains the mappings between these references and the actual strings. This allows the offline parser to obtain the strings from the dictionary to parse the log messages. This binary format allows a more compact representation of log messages in certain scenarios. However, this requires the use of an offline parser and is not as intuitive to use as text-based log messages.

Note that long double is not supported by Python’s struct module. Therefore, log messages with long double will not display the correct values.

Configuration

Here are kconfig options related to dictionary-based logging:

CONFIG_LOG_DICTIONARY_SUPPORT enables dictionary-based logging support. This should be selected by the backends which require it.
The UART backend can be used for dictionary-based logging. These are additional config for the UART backend:
- CONFIG_LOG_BACKEND_UART_OUTPUT_DICTIONARY_HEX tells the UART backend to output hexadecimal characters for dictionary based logging. This is useful when the log data needs to be captured manually via terminals and consoles.
- CONFIG_LOG_BACKEND_UART_OUTPUT_DICTIONARY_BIN tells the UART backend to output binary data.

Usage

When dictionary-based logging is enabled via enabling related logging backends, a JSON database file, named log_dictionary.json, will be created in the build directory. This database file contains information for the parser to correctly parse the log data. Note that this database file only works with the same build, and cannot be used for any other builds.

To use the log parser:

./scripts/logging/dictionary/log_parser.py <build dir>/log_dictionary.json <log data file>

The parser takes two required arguments, where the first one is the full path to the JSON database file, and the second part is the file containing log data. Add an optional argument --hex to the end if the log data file contains hexadecimal characters (e.g. when CONFIG_LOG_BACKEND_UART_OUTPUT_DICTIONARY_HEX=y). This tells the parser to convert the hexadecimal characters to binary before parsing.

Please refer to Dictionary-based Logging Sample on how to use the log parser.

Recommendations 

The are following recommendations:

Enable CONFIG_LOG_SPEED to slightly speed up deferred logging at the cost of slight increase in memory footprint.
Compiler with C11 _Generic keyword support is recommended. Logging performance is significantly degraded without it. See Cbprintf Packaging.
It is recommended to cast pointer to const char * when it is used with %s format specifier and it points to a constant string.
It is recommended to cast pointer to char * when it is used with %s format specifier and it points to a transient string.
It is recommended to cast character pointer to non character pointer (e.g., void *) when it is used with %p format specifier.

LOG_WRN("%s", str);
LOG_WRN("%p", (void *)str);

Benchmark 

Benchmark numbers from tests/subsys/logging/log_benchmark performed on qemu_x86. It is a rough comparison to give a general overview.

Feature
Kernel logging	7us [3]/11us
User logging	13us
kernel logging with overwrite	10us [3]/15us
Logging transient string	42us
Logging transient string from user	50us
Memory utilization [4]	518
Memory footprint (test) [5]	2k
Memory footprint (application) [6]	3.5k
Message footprint [7]	47 [3]/32 bytes

Benchmark details

Stack usage 

When logging is enabled it impacts stack usage of the context that uses logging API. If stack is optimized it may lead to stack overflow. Stack usage depends on mode and optimization. It also significantly varies between platforms. In general, when CONFIG_LOG_MODE_DEFERRED is used stack usage is smaller since logging is limited to creating and storing log message. When CONFIG_LOG_MODE_IMMEDIATE is used then log message is processed by the backend which includes string formatting. In case of that mode, stack usage will depend on which backends are used.

tests/subsys/logging/log_stack test is used to characterize stack usage depending on mode, optimization and platform used. Test is using only the default backend.

Some of the platforms characterization for log message with two integer arguments listed below:

Platform	Deferred	Deferred (no optimization)	Immediate	Immediate (no optimization)
ARM Cortex-M3	40	152	412	783
x86	12	224	388	796
riscv32	24	208	456	844
xtensa	72	336	504	944
x86_64	32	528	1088	1440

API Reference 

Logger API 

group log_api

Logger API.

Defines

LOG_ERR(...)

Writes an ERROR level message to the log.

It’s meant to report severe errors, such as those from which it’s not possible to recover.

Parameters:

... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_WRN(...)

Writes a WARNING level message to the log.

It’s meant to register messages related to unusual situations that are not necessarily errors.

Parameters:

... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_INF(...)

Writes an INFO level message to the log.

It’s meant to write generic user oriented messages.

Parameters:

... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_DBG(...)

Writes a DEBUG level message to the log.

It’s meant to write developer oriented information.

Parameters:

... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_PRINTK(...)

Unconditionally print raw log message.

The result is same as if printk was used but it goes through logging infrastructure thus utilizes logging mode, e.g. deferred mode.

Parameters:

... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_RAW(...)

Unconditionally print raw log message.

Provided string is printed as is without appending any characters (e.g., color or newline).

Parameters:

... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_INST_ERR(_log_inst, ...)

Writes an ERROR level message associated with the instance to the log.

Message is associated with specific instance of the module which has independent filtering settings (if runtime filtering is enabled) and message prefix (<module_name>.<instance_name>). It’s meant to report severe errors, such as those from which it’s not possible to recover.

Parameters:

_log_inst – Pointer to the log structure associated with the instance.
... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_INST_WRN(_log_inst, ...)

Writes a WARNING level message associated with the instance to the log.

Message is associated with specific instance of the module which has independent filtering settings (if runtime filtering is enabled) and message prefix (<module_name>.<instance_name>). It’s meant to register messages related to unusual situations that are not necessarily errors.

Parameters:

_log_inst – Pointer to the log structure associated with the instance.
... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_INST_INF(_log_inst, ...)

Writes an INFO level message associated with the instance to the log.

Message is associated with specific instance of the module which has independent filtering settings (if runtime filtering is enabled) and message prefix (<module_name>.<instance_name>). It’s meant to write generic user oriented messages.

Parameters:

_log_inst – Pointer to the log structure associated with the instance.
... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_INST_DBG(_log_inst, ...)

Writes a DEBUG level message associated with the instance to the log.

Message is associated with specific instance of the module which has independent filtering settings (if runtime filtering is enabled) and message prefix (<module_name>.<instance_name>). It’s meant to write developer oriented information.

Parameters:

_log_inst – Pointer to the log structure associated with the instance.
... – A string optionally containing printk valid conversion specifier, followed by as many values as specifiers.

LOG_HEXDUMP_ERR(_data, _length, _str)

Writes an ERROR level hexdump message to the log.

It’s meant to report severe errors, such as those from which it’s not possible to recover.

Parameters:

_data – Pointer to the data to be logged.
_length – Length of data (in bytes).
_str – Persistent, raw string.

LOG_HEXDUMP_WRN(_data, _length, _str)

Writes a WARNING level message to the log.

It’s meant to register messages related to unusual situations that are not necessarily errors.

Parameters:

_data – Pointer to the data to be logged.
_length – Length of data (in bytes).
_str – Persistent, raw string.

LOG_HEXDUMP_INF(_data, _length, _str)

Writes an INFO level message to the log.

It’s meant to write generic user oriented messages.

Parameters:

_data – Pointer to the data to be logged.
_length – Length of data (in bytes).
_str – Persistent, raw string.

LOG_HEXDUMP_DBG(_data, _length, _str)

Writes a DEBUG level message to the log.

It’s meant to write developer oriented information.

Parameters:

_data – Pointer to the data to be logged.
_length – Length of data (in bytes).
_str – Persistent, raw string.

LOG_INST_HEXDUMP_ERR(_log_inst, _data, _length, _str)

Writes an ERROR hexdump message associated with the instance to the log.

Message is associated with specific instance of the module which has independent filtering settings (if runtime filtering is enabled) and message prefix (<module_name>.<instance_name>). It’s meant to report severe errors, such as those from which it’s not possible to recover.

Parameters:

_log_inst – Pointer to the log structure associated with the instance.
_data – Pointer to the data to be logged.
_length – Length of data (in bytes).
_str – Persistent, raw string.

LOG_INST_HEXDUMP_WRN(_log_inst, _data, _length, _str)

Writes a WARNING level hexdump message associated with the instance to the log.

It’s meant to register messages related to unusual situations that are not necessarily errors.

Parameters:

_log_inst – Pointer to the log structure associated with the instance.
_data – Pointer to the data to be logged.
_length – Length of data (in bytes).
_str – Persistent, raw string.

LOG_INST_HEXDUMP_INF(_log_inst, _data, _length, _str)

Writes an INFO level hexdump message associated with the instance to the log.

It’s meant to write generic user oriented messages.

Parameters:

_log_inst – Pointer to the log structure associated with the instance.
_data – Pointer to the data to be logged.
_length – Length of data (in bytes).
_str – Persistent, raw string.

LOG_INST_HEXDUMP_DBG(_log_inst, _data, _length, _str)

Writes a DEBUG level hexdump message associated with the instance to the log.

It’s meant to write developer oriented information.

Parameters:

_log_inst – Pointer to the log structure associated with the instance.
_data – Pointer to the data to be logged.
_length – Length of data (in bytes).
_str – Persistent, raw string.

LOG_MODULE_REGISTER(...)

Create module-specific state and register the module with Logger.

This macro normally must be used after including <zephyr/logging/log.h> to complete the initialization of the module.

Module registration can be skipped in two cases:

The module consists of more than one file, and another file invokes this macro. (LOG_MODULE_DECLARE() should be used instead in all of the module’s other files.)
Instance logging is used and there is no need to create module entry. In that case LOG_LEVEL_SET() should be used to set log level used within the file.

Macro accepts one or two parameters:

module name
optional log level. If not provided then default log level is used in the file.

Example usage:

LOG_MODULE_REGISTER(foo, CONFIG_FOO_LOG_LEVEL)
LOG_MODULE_REGISTER(foo)

Logger control 

group log_ctrl

Logger control API.

Defines

LOG_CORE_INIT()

LOG_INIT()

LOG_PANIC()

LOG_PROCESS()

Typedefs

typedef log_timestamp_t (*log_timestamp_get_t)(void)

Functions

void log_core_init(void)

Function system initialization of the logger.

Function is called during start up to allow logging before user can explicitly initialize the logger.

void log_init(void): Function for user initialization of the logger.

void log_thread_set(k_tid_t process_tid)

Function for providing thread which is processing logs.

See CONFIG_LOG_PROCESS_TRIGGER_THRESHOLD.

Note

Function has asserts and has no effect when CONFIG_LOG_PROCESS_THREAD is set.

Parameters:

process_tid – Process thread id. Used to wake up the thread.

int log_set_timestamp_func(log_timestamp_get_t timestamp_getter, uint32_t freq)

Function for providing timestamp function.

Parameters:

timestamp_getter – Timestamp function.
freq – Timestamping frequency.

Returns:

0 on success or error.

void log_panic(void)

Switch the logger subsystem to the panic mode.

Returns immediately if the logger is already in the panic mode.

On panic the logger subsystem informs all backends about panic mode. Backends must switch to blocking mode or halt. All pending logs are flushed after switching to panic mode. In panic mode, all log messages must be processed in the context of the call.

bool log_process(void)

Process one pending log message.

Return values:

true – There is more messages pending to be processed.
false – No messages pending.

uint32_t log_buffered_cnt(void)

Return number of buffered log messages.

Returns:: Number of currently buffered log messages.

uint32_t log_src_cnt_get(uint32_t domain_id)

Get number of independent logger sources (modules and instances)

Parameters:

domain_id – Domain ID.

Returns:

Number of sources.

const char *log_source_name_get(uint32_t domain_id, uint32_t source_id)

Get name of the source (module or instance).

Parameters:

domain_id – Domain ID.
source_id – Source ID.

Returns:

Source name or NULL if invalid arguments.

static inline uint8_t log_domains_count(void)

Return number of domains present in the system.

There will be at least one local domain.

Returns:: Number of domains.

const char *log_domain_name_get(uint32_t domain_id)

Get name of the domain.

Parameters:

domain_id – Domain ID.

Returns:

Domain name.

int log_source_id_get(const char *name)

Function for finding source ID based on source name.

Parameters:

name – Source name

Returns:

Source ID or negative number when source ID is not found.

uint32_t log_filter_get(struct log_backend const *const backend, uint32_t domain_id, int16_t source_id, bool runtime)

Get source filter for the provided backend.

Parameters:

backend – Backend instance.
domain_id – ID of the domain.
source_id – Source (module or instance) ID.
runtime – True for runtime filter or false for compiled in.

Returns:

Severity level.

uint32_t log_filter_set(struct log_backend const *const backend, uint32_t domain_id, int16_t source_id, uint32_t level)

Set filter on given source for the provided backend.

Parameters:

backend – Backend instance. NULL for all backends.
domain_id – ID of the domain.
source_id – Source (module or instance) ID.
level – Severity level.

Returns:

Actual level set which may be limited by compiled level. If filter was set for all backends then maximal level that was set is returned.

void log_backend_enable(struct log_backend const *const backend, void *ctx, uint32_t level)

Enable backend with initial maximum filtering level.

Parameters:

backend – Backend instance.
ctx – User context.
level – Severity level.

void log_backend_disable(struct log_backend const *const backend)

Disable backend.

Parameters:

backend – Backend instance.

const struct log_backend *log_backend_get_by_name(const char *backend_name)

Get backend by name.

Parameters:

backend_name – [in] Name of the backend as defined by the LOG_BACKEND_DEFINE.

Return values:

Pointer – to the backend instance if found, NULL if backend is not found.

const struct log_backend *log_format_set_all_active_backends(size_t log_type)

Sets logging format for all active backends.

Parameters:

log_type – Log format.

Return values:

Pointer – to the last backend that failed, NULL for success.

static inline bool log_data_pending(void)

Check if there is pending data to be processed by the logging subsystem.

Function can be used to determine if all logs have been flushed. Function returns false when deferred mode is not enabled.

Return values:

true – There is pending data.
false – No pending data to process.

int log_set_tag(const char *tag)

Configure tag used to prefix each message.

Parameters:

tag – Tag.

Return values:

0 – on successful operation.
-ENOTSUP – if feature is disabled.
-ENOMEM – if string is longer than the buffer capacity. Tag will be trimmed.

int log_mem_get_usage(uint32_t *buf_size, uint32_t *usage)

Get current memory usage.

Parameters:

buf_size – [out] Capacity of the buffer used for storing log messages.
usage – [out] Number of bytes currently containing pending log messages.

Return values:

-EINVAL – if logging mode does not use the buffer.
0 – successfully collected usage data.

int log_mem_get_max_usage(uint32_t *max)

Get maximum memory usage.

Requires CONFIG_LOG_MEM_UTILIZATION option.

Parameters:

max – [out] Maximum number of bytes used for pending log messages.

Return values:

-EINVAL – if logging mode does not use the buffer.
-ENOTSUP – if instrumentation is not enabled. not been enabled.
0 – successfully collected usage data.

Log message 

group log_msg

Log message API.

Defines

LOG_MSG_GENERIC_HDR

Functions

static inline uint32_t log_msg_get_total_wlen(const struct log_msg_desc desc)

Get total length (in 32 bit words) of a log message.

Parameters:

desc – Log message descriptor.

Returns:

Length.

static inline uint32_t log_msg_generic_get_wlen(const union mpsc_pbuf_generic *item)

Get length of the log item.

Parameters:

item – Item.

Returns:

Length in 32 bit words.

static inline uint8_t log_msg_get_domain(struct log_msg *msg)

Get log message domain ID.

Parameters:

msg – Log message.

Returns:

Domain ID

static inline uint8_t log_msg_get_level(struct log_msg *msg)

Get log message level.

Parameters:

msg – Log message.

Returns:

Log level.

static inline const void *log_msg_get_source(struct log_msg *msg)

Get message source data.

Parameters:

msg – Log message.

Returns:

Pointer to the source data.

static inline log_timestamp_t log_msg_get_timestamp(struct log_msg *msg)

Get timestamp.

Parameters:

msg – Log message.

Returns:

Timestamp.

static inline void *log_msg_get_tid(struct log_msg *msg)

Get Thread ID.

Parameters:

msg – Log message.

Returns:

Thread ID.

static inline uint8_t *log_msg_get_data(struct log_msg *msg, size_t *len)

Get data buffer.

Parameters:

msg – log message.
len – location where data length is written.

Returns:

pointer to the data buffer.

static inline uint8_t *log_msg_get_package(struct log_msg *msg, size_t *len)

Get string package.

Parameters:

msg – log message.
len – location where string package length is written.

Returns:

pointer to the package.

struct log_msg_desc: #include <log_msg.h>

union log_msg_source

#include <log_msg.h>

Public Members

const struct log_source_const_data *fixed

struct log_source_dynamic_data *dynamic

void *raw

struct log_msg_hdr: #include <log_msg.h>

struct log_msg: #include <log_msg.h>

struct log_msg_generic_hdr: #include <log_msg.h>

union log_msg_generic

#include <log_msg.h>

Public Members

union mpsc_pbuf_generic buf

struct log_msg_generic_hdr generic

struct log_msg log

Logger backend interface 

group log_backend

Logger backend interface.

Defines

LOG_BACKEND_DEFINE(_name, _api, _autostart, ...)

Macro for creating a logger backend instance.

Parameters:

_name – Name of the backend instance.
_api – Logger backend API.
_autostart – If true backend is initialized and activated together with the logger subsystem.
... – Optional context.

Enums

enum log_backend_evt

Backend events.

Values:

enumerator LOG_BACKEND_EVT_PROCESS_THREAD_DONE

Event when process thread finishes processing.

This event is emitted when the process thread finishes processing pending log messages.

Note

This is not emitted when there are no pending log messages being processed.

Note

Deferred mode only.

enumerator LOG_BACKEND_EVT_MAX: Maximum number of backend events.

Functions

static inline void log_backend_init(const struct log_backend *const backend)

Initialize or initiate the logging backend.

If backend initialization takes longer time it could block logging thread if backend is autostarted. That is because all backends are initilized in the context of the logging thread. In that case, backend shall provide function for polling for readiness (log_backend_is_ready).

Parameters:

backend – [in] Pointer to the backend instance.

static inline int log_backend_is_ready(const struct log_backend *const backend)

Poll for backend readiness.

If backend is ready immediately after initialization then backend may not provide this function.

Parameters:

backend – [in] Pointer to the backend instance.

Return values:

0 – if backend is ready.
-EBUSY – if backend is not yet ready.

static inline void log_backend_msg_process(const struct log_backend *const backend, union log_msg_generic *msg)

Process message.

Function is used in deferred and immediate mode. On return, message content is processed by the backend and memory can be freed.

Parameters:

backend – [in] Pointer to the backend instance.
msg – [in] Pointer to message with log entry.

static inline void log_backend_dropped(const struct log_backend *const backend, uint32_t cnt)

Notify backend about dropped log messages.

Function is optional.

Parameters:

backend – [in] Pointer to the backend instance.
cnt – [in] Number of dropped logs since last notification.

static inline void log_backend_panic(const struct log_backend *const backend)

Reconfigure backend to panic mode.

Parameters:

backend – [in] Pointer to the backend instance.

static inline void log_backend_id_set(const struct log_backend *const backend, uint8_t id)

Set backend id.

Note

It is used internally by the logger.

Parameters:

backend – Pointer to the backend instance.
id – ID.

static inline uint8_t log_backend_id_get(const struct log_backend *const backend)

Get backend id.

Note

It is used internally by the logger.

Parameters:

backend – [in] Pointer to the backend instance.

Returns:

Id.

static inline const struct log_backend *log_backend_get(uint32_t idx)

Get backend.

Parameters:

idx – [in] Pointer to the backend instance.

Returns:

Pointer to the backend instance.

static inline int log_backend_count_get(void)

Get number of backends.

Returns:: Number of backends.

static inline void log_backend_activate(const struct log_backend *const backend, void *ctx)

Activate backend.

Parameters:

backend – [in] Pointer to the backend instance.
ctx – [in] User context.

static inline void log_backend_deactivate(const struct log_backend *const backend)

Deactivate backend.

Parameters:

backend – [in] Pointer to the backend instance.

static inline bool log_backend_is_active(const struct log_backend *const backend)

Check state of the backend.

Parameters:

backend – [in] Pointer to the backend instance.

Returns:

True if backend is active, false otherwise.

static inline int log_backend_format_set(const struct log_backend *backend, uint32_t log_type)

Set logging format.

Parameters:

backend – Pointer to the backend instance.
log_type – Log format.

Return values:

-ENOTSUP – If the backend does not support changing format types.
-EINVAL – If the input is invalid.
0 – for success.

static inline void log_backend_notify(const struct log_backend *const backend, enum log_backend_evt event, union log_backend_evt_arg *arg)

Notify a backend of an event.

Parameters:

backend – Pointer to the backend instance.
event – Event to be notified.
arg – Pointer to the argument(s).

union log_backend_evt_arg

#include <log_backend.h>

Argument(s) for backend events.

Public Members

void *raw: Unspecified argument(s).

struct log_backend_api: #include <log_backend.h>

Logger backend API.

struct log_backend_control_block: #include <log_backend.h>

Logger backend control block.

struct log_backend: #include <log_backend.h>

Logger backend structure.

Logger output formatting 

group log_output

Log output API.

Unnamed Group

void log_custom_output_msg_process(const struct log_output *log_output, struct log_msg *msg, uint32_t flags)

Custom logging output formatting.

Process log messages from an external output function set with log_custom_output_msg_set

Function is using provided context with the buffer and output function to process formatted string and output the data.

Parameters:

log_output – Pointer to the log output instance.
msg – Log message.
flags – Optional flags.

Defines

LOG_OUTPUT_TEXT: Supported backend logging format types for use with log_format_set() API to switch log format at runtime.

LOG_OUTPUT_SYST

LOG_OUTPUT_DICT

LOG_OUTPUT_CUSTOM

LOG_OUTPUT_DEFINE(_name, _func, _buf, _size)

Create log_output instance.

Parameters:

_name – Instance name.
_func – Function for processing output data.
_buf – Pointer to the output buffer.
_size – Size of the output buffer.

Typedefs

typedef int (*log_output_func_t)(uint8_t *buf, size_t size, void *ctx)

Prototype of the function processing output data.

Note

If the log output function cannot process all of the data, it is its responsibility to mark them as dropped or discarded by returning the corresponding number of bytes dropped or discarded to the caller.

Param buf:: The buffer data.
Param size:: The buffer size.
Param ctx:: User context.
Return:: Number of bytes processed, dropped or discarded.

typedef void (*log_format_func_t)(const struct log_output *output, struct log_msg *msg, uint32_t flags)

Typedef of the function pointer table “format_table”.

Param output:: Pointer to log_output struct.
Param msg:: Pointer to log_msg struct.
Param flags:: Flags used for text formatting options.
Return:: Function pointer based on Kconfigs defined for backends.

Functions

log_format_func_t log_format_func_t_get(uint32_t log_type): Declaration of the get routine for function pointer table format_table.

void log_output_msg_process(const struct log_output *log_output, struct log_msg *msg, uint32_t flags)

Process log messages v2 to readable strings.

Function is using provided context with the buffer and output function to process formatted string and output the data.

Parameters:

log_output – Pointer to the log output instance.
msg – Log message.
flags – Optional flags. See Log output formatting flags..

void log_output_process(const struct log_output *log_output, log_timestamp_t timestamp, const char *domain, const char *source, const k_tid_t tid, uint8_t level, const uint8_t *package, const uint8_t *data, size_t data_len, uint32_t flags)

Process input data to a readable string.

Parameters:

log_output – Pointer to the log output instance.
timestamp – Timestamp.
domain – Domain name string. Can be NULL.
source – Source name string. Can be NULL.
tid – Thread ID.
level – Criticality level.
package – Cbprintf package with a logging message string.
data – Data passed to hexdump API. Can bu NULL.
data_len – Data length.
flags – Formatting flags. See Log output formatting flags..

void log_output_msg_syst_process(const struct log_output *log_output, struct log_msg *msg, uint32_t flags)

Process log messages v2 to SYS-T format.

Function is using provided context with the buffer and output function to process formatted string and output the data in sys-t log output format.

Parameters:

log_output – Pointer to the log output instance.
msg – Log message.
flags – Optional flags. See Log output formatting flags..

void log_output_dropped_process(const struct log_output *output, uint32_t cnt)

Process dropped messages indication.

Function prints error message indicating lost log messages.

Parameters:

output – Pointer to the log output instance.
cnt – Number of dropped messages.

void log_output_flush(const struct log_output *output)

Flush output buffer.

Parameters:

output – Pointer to the log output instance.

static inline void log_output_ctx_set(const struct log_output *output, void *ctx)

Function for setting user context passed to the output function.

Parameters:

output – Pointer to the log output instance.
ctx – User context.

static inline void log_output_hostname_set(const struct log_output *output, const char *hostname)

Function for setting hostname of this device.

Parameters:

output – Pointer to the log output instance.
hostname – Hostname of this device

void log_output_timestamp_freq_set(uint32_t freq)

Set timestamp frequency.

Parameters:

freq – Frequency in Hz.

uint64_t log_output_timestamp_to_us(log_timestamp_t timestamp)

Convert timestamp of the message to us.

Parameters:

timestamp – Message timestamp

Returns:

Timestamp value in us.

struct log_output_control_block: #include <log_output.h>

struct log_output: #include <log_output.h>

Log_output instance structure.