[RFC,v1,01/20] libcamera: sysfs: Add devicePath() helpers

28313 diff mbox series

Add sysfs::devicePath() helpers to resolve the sysfs path of the device
via a character device from either the device node or the device major
and minor numbers.

The helper is used in V4L2Device::devicePath(), replacing the baked in
logic there.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
---
 include/libcamera/internal/sysfs.h |  3 ++
 src/libcamera/sysfs.cpp            | 61 ++++++++++++++++++++++++++++++
 src/libcamera/v4l2_device.cpp      | 13 ++-----
 3 files changed, 67 insertions(+), 10 deletions(-)

Hi

2026. 09. 18. 9:59 keltezéssel, Naushir Patuck írta:
> Add sysfs::devicePath() helpers to resolve the sysfs path of the device
> via a character device from either the device node or the device major
> and minor numbers.
> 
> The helper is used in V4L2Device::devicePath(), replacing the baked in
> logic there.
> 
> Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
> ---
>   include/libcamera/internal/sysfs.h |  3 ++
>   src/libcamera/sysfs.cpp            | 61 ++++++++++++++++++++++++++++++
>   src/libcamera/v4l2_device.cpp      | 13 ++-----
>   3 files changed, 67 insertions(+), 10 deletions(-)
> 
> diff --git a/include/libcamera/internal/sysfs.h b/include/libcamera/internal/sysfs.h
> index aca60fb6c8ab..1b30317c0dea 100644
> --- a/include/libcamera/internal/sysfs.h
> +++ b/include/libcamera/internal/sysfs.h
> @@ -15,6 +15,9 @@ namespace sysfs {
>   
>   std::string charDevPath(const std::string &deviceNode);
>   
> +std::string devicePath(const std::string &deviceNode);
> +std::string devicePath(unsigned int deviceMajor, unsigned int deviceMinor);
> +
>   std::string firmwareNodePath(const std::string &device);
>   
>   } /* namespace sysfs */
> diff --git a/src/libcamera/sysfs.cpp b/src/libcamera/sysfs.cpp
> index 3d9885b080c6..7c441a17f86d 100644
> --- a/src/libcamera/sysfs.cpp
> +++ b/src/libcamera/sysfs.cpp
> @@ -9,6 +9,7 @@
>   
>   #include <fstream>
>   #include <sstream>
> +#include <stdlib.h>
>   #include <sys/stat.h>
>   #include <sys/sysmacros.h>
>   
> @@ -26,6 +27,26 @@ LOG_DEFINE_CATEGORY(SysFs)
>   
>   namespace sysfs {
>   
> +namespace {
> +

Let's make some small optimizations with this move.


> +/*
> + * Resolve the "device" symbolic link of a sysfs character device directory to
> + * the sysfs path of the physical device associated with it.
> + */
> +std::string resolveDevicePath(const std::string &charDevDir)

   std::string charDevDir


> +{
> +	char *realPath = realpath((charDevDir + "/device").c_str(), nullptr);

   (std::move(charDevDir) + "/device").c_str()


> +	if (!realPath)
> +		return {};
> +
> +	std::string path{ realPath };
> +	free(realPath);
> +
> +	return path;
> +}
> +
> +} /* namespace */
> +
>   /**
>    * \brief Retrieve the sysfs path for a character device
>    * \param[in] deviceNode Path to character device node
> @@ -49,6 +70,46 @@ std::string charDevPath(const std::string &deviceNode)
>   	return dev.str();
>   }
>   
> +/**
> + * \brief Retrieve the sysfs path of the physical device for a character device
> + * \param[in] deviceNode Path to character device node
> + *
> + * Retrieve the sysfs path of the physical device associated with the character
> + * device \a deviceNode. The path is absolute and contains no symbolic link.
> + *
> + * \return The device path on success or an empty string on failure
> + */
> +std::string devicePath(const std::string &deviceNode)
> +{
> +	std::string path = charDevPath(deviceNode);
> +	if (path.empty())
> +		return {};
> +
> +	return resolveDevicePath(path);

   std::move(path)


> +}
> +
> +/**
> + * \brief Retrieve the sysfs path of the physical device for a character device
> + * \param[in] deviceMajor The character device major number
> + * \param[in] deviceMinor The character device minor number
> + *
> + * Retrieve the sysfs path of the physical device associated with the character
> + * device identified by \a deviceMajor and \a deviceMinor. The path is absolute
> + * and contains no symbolic link.
> + *
> + * Unlike the device node variant of this function, resolving the device from
> + * its device numbers requires no access to the device node itself.
> + *
> + * \return The device path on success or an empty string on failure
> + */
> +std::string devicePath(unsigned int deviceMajor, unsigned int deviceMinor)
> +{
> +	std::ostringstream dev("/sys/dev/char/", std::ios_base::ate);
> +	dev << deviceMajor << ":" << deviceMinor;
> +
> +	return resolveDevicePath(dev.str());

   std::move(dev).str()


> +}
> +
>   /**
>    * \brief Retrieve the path of the firmware node for a device
>    * \param[in] device Path in sysfs to search
> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> index 258c82b8d238..8b9c3a357149 100644
> --- a/src/libcamera/v4l2_device.cpp
> +++ b/src/libcamera/v4l2_device.cpp
> @@ -454,17 +454,10 @@ const struct v4l2_query_ext_ctrl *V4L2Device::controlInfo(uint32_t id) const
>    */
>   std::string V4L2Device::devicePath() const
>   {
> -	std::string devicePath = sysfs::charDevPath(deviceNode_) + "/device";
> -
> -	char *realPath = realpath(devicePath.c_str(), nullptr);
> -	if (!realPath) {
> +	std::string path = sysfs::devicePath(deviceNode_);
> +	if (path.empty())
>   		LOG(V4L2, Fatal)
> -			<< "Can not resolve device path for " << devicePath;
> -		return {};
> -	}
> -
> -	std::string path{ realPath };
> -	free(realPath);
> +			<< "Can not resolve device path for " << deviceNode_;
>   
>   	return path;
>   }