[v18,03/12] config: Add configuration retrieval helpers

24354 diff mbox series

Let's add some helpers to make accessing simple configuration values
simpler.  The helpers are used in the followup patches.

GlobalConfiguration::option ensures that no value is returned rather
than a value of YamlObject::empty.

Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
---
 .../libcamera/internal/global_configuration.h | 28 ++++++
 src/libcamera/global_configuration.cpp        | 99 +++++++++++++++++++
 2 files changed, 127 insertions(+)

On Fri, Sep 12, 2025 at 04:29:04PM +0200, Milan Zamazal wrote:
> Let's add some helpers to make accessing simple configuration values
> simpler.  The helpers are used in the followup patches.
> 
> GlobalConfiguration::option ensures that no value is returned rather
> than a value of YamlObject::empty.
> 
> Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
> Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
> ---
>  .../libcamera/internal/global_configuration.h | 28 ++++++
>  src/libcamera/global_configuration.cpp        | 99 +++++++++++++++++++
>  2 files changed, 127 insertions(+)
> 
> diff --git a/include/libcamera/internal/global_configuration.h b/include/libcamera/internal/global_configuration.h
> index f695498c4..8d09517ed 100644
> --- a/include/libcamera/internal/global_configuration.h
> +++ b/include/libcamera/internal/global_configuration.h
> @@ -8,6 +8,11 @@
>  #pragma once
>  
>  #include <filesystem>
> +#include <optional>
> +#include <string>
> +#include <string_view>
> +
> +#include <libcamera/base/utils.h>
>  
>  #include "libcamera/internal/yaml_parser.h"
>  
> @@ -23,6 +28,29 @@ public:
>  	unsigned int version() const;
>  	Configuration configuration() const;
>  
> +	template<typename T>
> +	std::optional<T> option(
> +		const std::initializer_list<std::string_view> confPath) const
> +	{
> +		const YamlObject *c = &configuration();
> +		for (auto part : confPath) {
> +			c = &(*c)[part];
> +			if (!*c)
> +				return {};
> +		}
> +		return c->get<T>();
> +	}
> +
> +	std::optional<std::vector<std::string>> listOption(
> +		const std::initializer_list<std::string_view> confPath) const;
> +	std::optional<std::string> envOption(
> +		const char *const envVariable,
> +		const std::initializer_list<std::string_view> confPath) const;
> +	std::optional<std::vector<std::string>> envListOption(
> +		const char *const envVariable,
> +		const std::initializer_list<std::string_view> confPath,
> +		const std::string delimiter = ":") const;
> +
>  private:
>  	bool loadFile(const std::filesystem::path &fileName);
>  	void load();
> diff --git a/src/libcamera/global_configuration.cpp b/src/libcamera/global_configuration.cpp
> index d02668111..592edcf30 100644
> --- a/src/libcamera/global_configuration.cpp
> +++ b/src/libcamera/global_configuration.cpp
> @@ -8,8 +8,12 @@
>  #include "libcamera/internal/global_configuration.h"
>  
>  #include <filesystem>
> +#include <memory>
> +#include <optional>
> +#include <string>
>  #include <string_view>
>  #include <sys/types.h>
> +#include <vector>
>  
>  #include <libcamera/base/file.h>
>  #include <libcamera/base/log.h>
> @@ -43,6 +47,12 @@ LOG_DEFINE_CATEGORY(Configuration)
>   * If the first found configuration file cannot be opened or parsed, an error is
>   * reported and no configuration file is used. This is to prevent libcamera from
>   * using an unintended configuration file.
> + *
> + * The configuration can be accessed using the provided helpers. Namely
> + * GlobalConfiguration::option(), GlobalConfiguration::envOption(),
> + * GlobalConfiguration::listOption(), and GlobalConfiguration::envListOption()
> + * to access individual options, or GlobalConfiguration::configuration() to
> + * access the whole configuration.

You can drop the class name, doxygen should resolve function names as
we're in the class scope.

>   */
>  
>  bool GlobalConfiguration::loadFile(const std::filesystem::path &fileName)
> @@ -110,6 +120,95 @@ GlobalConfiguration::GlobalConfiguration()
>   * the underlying type.
>   */
>  
> +/**
> + * \fn std::optional<T> GlobalConfiguration::option(const std::initializer_list<std::string_view> &confPath) const
> + * \brief Return value of the configuration option identified by \a confPath

s/Return/Retrieve the/

and s/identified by // to shorten the line.

Same below.

> + * \param[in] confPath Sequence of the YAML section names (excluding
> + * `configuration') leading to the requested option
> + * \return The value of the configuration item corresponding to \a confPath if
> + * it exists in the configuration file, or no value otherwise
> + */
> +
> +/**
> + * \brief Return values of the configuration option identified by \a confPath
> + * \tparam T The type of the retrieved configuration value
> + * \param[in] confPath Sequence of the YAML section names (excluding
> + * `configuration') leading to the requested list option, separated by dots
> + * \return A vector of strings or no value if not found
> + */
> +std::optional<std::vector<std::string>> GlobalConfiguration::listOption(
> +	const std::initializer_list<std::string_view> confPath) const
> +{
> +	const YamlObject *c = &configuration();
> +	for (auto part : confPath) {
> +		c = &(*c)[part];
> +		if (!*c)
> +			return {};
> +	}
> +	return c->getList<std::string>();
> +}
> +
> +/**
> + * \brief Return value of environment variable with a fallback on the configuration file
> + * \param[in] envVariable Environment variable to get the value from
> + * \param[in] confPath The sequence of YAML section names to fall back on when
> + * \a envVariable is unavailable
> + *
> + * This helper looks first at the given environment variable and if it is
> + * defined then it returns its value (even if it is empty). Otherwise it looks
> + * for \a confPath the same way as in GlobalConfiguration::option. Only string
> + * values are supported.
> + *
> + * \note Support for using environment variables to configure libcamera behavior
> + * is provided here mostly for backward compatibility reasons. Introducing new
> + * configuration environment variables is discouraged.
> + *
> + * \return The value retrieved from the given environment if it is set,
> + * otherwise the value from the configuration file if it exists, or no value if
> + * it does not
> + */
> +std::optional<std::string> GlobalConfiguration::envOption(
> +	const char *envVariable,
> +	const std::initializer_list<std::string_view> confPath) const
> +{
> +	const char *envValue = utils::secure_getenv(envVariable);
> +	if (envValue)
> +		return std::optional{ std::string{ envValue } };
> +	return option<std::string>(confPath);
> +}
> +
> +/**
> + * \brief Return values of the configuration option from a file or environment
> + * \param[in] envVariable Environment variable to get the value from
> + * \param[in] confPath The same as in GlobalConfiguration::option
> + * \param[in] delimiter Items separator in the environment variable
> + *
> + * This helper looks first at the given environment variable and if it is
> + * defined (even if it is empty) then it splits its value by semicolons and
> + * returns the resulting list of strings. Otherwise it looks for \a confPath the
> + * same way as in GlobalConfiguration::option, value of which must be a list of
> + * strings.
> + *
> + * \note Support for using environment variables to configure libcamera behavior
> + * is provided here mostly for backward compatibility reasons. Introducing new
> + * configuration environment variables is discouraged.
> + *
> + * \return A vector of strings retrieved from the given environment option or
> + * configuration file or no value if not found; the vector may be empty
> + */
> +std::optional<std::vector<std::string>> GlobalConfiguration::envListOption(
> +	const char *const envVariable,
> +	const std::initializer_list<std::string_view> confPath,
> +	const std::string delimiter) const

I think it's more logical to keep the envVariable and delimiter
arguments grouped together, as the delimiter refers to the environment
variable. I'll swap them, and adjust the envOption() arguments for
consistency.

> +{
> +	const char *envValue = utils::secure_getenv(envVariable);
> +	if (envValue) {
> +		auto items = utils::split(envValue, delimiter);
> +		return std::vector<std::string>(items.begin(), items.end());
> +	}
> +	return listOption(confPath);
> +}

I have a few ideas for improvements in these helpers, I'll send RFC
patches.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> +
>  /**
>   * \brief Return configuration version
>   *

On Sun, Sep 21, 2025 at 07:43:42AM +0300, Laurent Pinchart wrote:
> On Fri, Sep 12, 2025 at 04:29:04PM +0200, Milan Zamazal wrote:
> > Let's add some helpers to make accessing simple configuration values
> > simpler.  The helpers are used in the followup patches.
> > 
> > GlobalConfiguration::option ensures that no value is returned rather
> > than a value of YamlObject::empty.
> > 
> > Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
> > Signed-off-by: Milan Zamazal <mzamazal@redhat.com>
> > ---
> >  .../libcamera/internal/global_configuration.h | 28 ++++++
> >  src/libcamera/global_configuration.cpp        | 99 +++++++++++++++++++
> >  2 files changed, 127 insertions(+)
> > 
> > diff --git a/include/libcamera/internal/global_configuration.h b/include/libcamera/internal/global_configuration.h
> > index f695498c4..8d09517ed 100644
> > --- a/include/libcamera/internal/global_configuration.h
> > +++ b/include/libcamera/internal/global_configuration.h
> > @@ -8,6 +8,11 @@
> >  #pragma once
> >  
> >  #include <filesystem>
> > +#include <optional>
> > +#include <string>
> > +#include <string_view>
> > +
> > +#include <libcamera/base/utils.h>
> >  
> >  #include "libcamera/internal/yaml_parser.h"
> >  
> > @@ -23,6 +28,29 @@ public:
> >  	unsigned int version() const;
> >  	Configuration configuration() const;
> >  
> > +	template<typename T>
> > +	std::optional<T> option(
> > +		const std::initializer_list<std::string_view> confPath) const
> > +	{
> > +		const YamlObject *c = &configuration();
> > +		for (auto part : confPath) {
> > +			c = &(*c)[part];
> > +			if (!*c)
> > +				return {};
> > +		}
> > +		return c->get<T>();
> > +	}
> > +
> > +	std::optional<std::vector<std::string>> listOption(
> > +		const std::initializer_list<std::string_view> confPath) const;
> > +	std::optional<std::string> envOption(
> > +		const char *const envVariable,
> > +		const std::initializer_list<std::string_view> confPath) const;
> > +	std::optional<std::vector<std::string>> envListOption(
> > +		const char *const envVariable,
> > +		const std::initializer_list<std::string_view> confPath,
> > +		const std::string delimiter = ":") const;
> > +
> >  private:
> >  	bool loadFile(const std::filesystem::path &fileName);
> >  	void load();
> > diff --git a/src/libcamera/global_configuration.cpp b/src/libcamera/global_configuration.cpp
> > index d02668111..592edcf30 100644
> > --- a/src/libcamera/global_configuration.cpp
> > +++ b/src/libcamera/global_configuration.cpp
> > @@ -8,8 +8,12 @@
> >  #include "libcamera/internal/global_configuration.h"
> >  
> >  #include <filesystem>
> > +#include <memory>
> > +#include <optional>
> > +#include <string>
> >  #include <string_view>
> >  #include <sys/types.h>
> > +#include <vector>
> >  
> >  #include <libcamera/base/file.h>
> >  #include <libcamera/base/log.h>
> > @@ -43,6 +47,12 @@ LOG_DEFINE_CATEGORY(Configuration)
> >   * If the first found configuration file cannot be opened or parsed, an error is
> >   * reported and no configuration file is used. This is to prevent libcamera from
> >   * using an unintended configuration file.
> > + *
> > + * The configuration can be accessed using the provided helpers. Namely
> > + * GlobalConfiguration::option(), GlobalConfiguration::envOption(),
> > + * GlobalConfiguration::listOption(), and GlobalConfiguration::envListOption()
> > + * to access individual options, or GlobalConfiguration::configuration() to
> > + * access the whole configuration.
> 
> You can drop the class name, doxygen should resolve function names as
> we're in the class scope.
> 
> >   */
> >  
> >  bool GlobalConfiguration::loadFile(const std::filesystem::path &fileName)
> > @@ -110,6 +120,95 @@ GlobalConfiguration::GlobalConfiguration()
> >   * the underlying type.
> >   */
> >  
> > +/**
> > + * \fn std::optional<T> GlobalConfiguration::option(const std::initializer_list<std::string_view> &confPath) const
> > + * \brief Return value of the configuration option identified by \a confPath
> 
> s/Return/Retrieve the/
> 
> and s/identified by // to shorten the line.
> 
> Same below.
> 
> > + * \param[in] confPath Sequence of the YAML section names (excluding
> > + * `configuration') leading to the requested option
> > + * \return The value of the configuration item corresponding to \a confPath if
> > + * it exists in the configuration file, or no value otherwise
> > + */
> > +
> > +/**
> > + * \brief Return values of the configuration option identified by \a confPath
> > + * \tparam T The type of the retrieved configuration value
> > + * \param[in] confPath Sequence of the YAML section names (excluding
> > + * `configuration') leading to the requested list option, separated by dots
> > + * \return A vector of strings or no value if not found
> > + */
> > +std::optional<std::vector<std::string>> GlobalConfiguration::listOption(
> > +	const std::initializer_list<std::string_view> confPath) const
> > +{
> > +	const YamlObject *c = &configuration();
> > +	for (auto part : confPath) {
> > +		c = &(*c)[part];
> > +		if (!*c)
> > +			return {};
> > +	}
> > +	return c->getList<std::string>();
> > +}
> > +
> > +/**
> > + * \brief Return value of environment variable with a fallback on the configuration file
> > + * \param[in] envVariable Environment variable to get the value from
> > + * \param[in] confPath The sequence of YAML section names to fall back on when
> > + * \a envVariable is unavailable
> > + *
> > + * This helper looks first at the given environment variable and if it is
> > + * defined then it returns its value (even if it is empty). Otherwise it looks
> > + * for \a confPath the same way as in GlobalConfiguration::option. Only string
> > + * values are supported.
> > + *
> > + * \note Support for using environment variables to configure libcamera behavior
> > + * is provided here mostly for backward compatibility reasons. Introducing new
> > + * configuration environment variables is discouraged.
> > + *
> > + * \return The value retrieved from the given environment if it is set,
> > + * otherwise the value from the configuration file if it exists, or no value if
> > + * it does not
> > + */
> > +std::optional<std::string> GlobalConfiguration::envOption(
> > +	const char *envVariable,
> > +	const std::initializer_list<std::string_view> confPath) const
> > +{
> > +	const char *envValue = utils::secure_getenv(envVariable);
> > +	if (envValue)
> > +		return std::optional{ std::string{ envValue } };
> > +	return option<std::string>(confPath);
> > +}
> > +
> > +/**
> > + * \brief Return values of the configuration option from a file or environment
> > + * \param[in] envVariable Environment variable to get the value from
> > + * \param[in] confPath The same as in GlobalConfiguration::option
> > + * \param[in] delimiter Items separator in the environment variable
> > + *
> > + * This helper looks first at the given environment variable and if it is
> > + * defined (even if it is empty) then it splits its value by semicolons and
> > + * returns the resulting list of strings. Otherwise it looks for \a confPath the
> > + * same way as in GlobalConfiguration::option, value of which must be a list of
> > + * strings.
> > + *
> > + * \note Support for using environment variables to configure libcamera behavior
> > + * is provided here mostly for backward compatibility reasons. Introducing new
> > + * configuration environment variables is discouraged.
> > + *
> > + * \return A vector of strings retrieved from the given environment option or
> > + * configuration file or no value if not found; the vector may be empty
> > + */
> > +std::optional<std::vector<std::string>> GlobalConfiguration::envListOption(
> > +	const char *const envVariable,
> > +	const std::initializer_list<std::string_view> confPath,
> > +	const std::string delimiter) const
> 
> I think it's more logical to keep the envVariable and delimiter
> arguments grouped together, as the delimiter refers to the environment
> variable. I'll swap them, and adjust the envOption() arguments for
> consistency.

Actually that would also require a change in the documentation. I'll
send a patch on top instead.

> > +{
> > +	const char *envValue = utils::secure_getenv(envVariable);
> > +	if (envValue) {
> > +		auto items = utils::split(envValue, delimiter);
> > +		return std::vector<std::string>(items.begin(), items.end());
> > +	}
> > +	return listOption(confPath);
> > +}
> 
> I have a few ideas for improvements in these helpers, I'll send RFC
> patches.
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> > +
> >  /**
> >   * \brief Return configuration version
> >   *