libcamera: utils: Add a function to retrieve the libcamera source tree

Similarly to libcameraBuildPath(), there's a need to locate resources
within the source tree when running libcamera without installing it.
Support this use case with a new utils::libcameraSourcePath() function.

The implementation uses a symlink from the build root to the source root
in order to avoid hardcoding the path to the source root in the
libcamera.so binary.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

meson.build

@@ -93,6 +93,12 @@ if get_option('test')
     subdir('test')
 endif
 
+# Create a symlink from the build root to the source root. This is used when
+# running libcamera from the build directory to locate resources in the source
+# directory (such as IPA configuration files).
+run_command('ln', '-fsT', meson.source_root(),
+            join_paths(meson.build_root(), 'source'))
+
 configure_file(output : 'config.h', configuration : config_h)
 
 pkg_mod = import('pkgconfig')

src/libcamera/include/utils.h

@@ -188,6 +188,7 @@ private:
 details::StringSplitter split(const std::string &str, const std::string &delim);
 
 std::string libcameraBuildPath();
+std::string libcameraSourcePath();
 
 } /* namespace utils */
 

src/libcamera/utils.cpp

@@ -10,10 +10,13 @@
 #include <dlfcn.h>
 #include <elf.h>
 #include <iomanip>
+#include <limits.h>
 #include <link.h>
 #include <sstream>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 #include <unistd.h>
 
 /**
@@ -360,9 +363,10 @@ bool isLibcameraInstalled()
  *
  * During development, it is useful to run libcamera binaries directly from the
  * build directory without installing them. This function helps components that
- * need to locate resources, such as IPA modules or IPA proxy workers, by
+ * need to locate resources in the build tree, such as IPA modules or IPA proxy
- * providing them with the path to the root of the build directory. Callers can
+ * workers, by providing them with the path to the root of the build directory.
- * then use it to complement or override searches in system-wide directories.
+ * Callers can then use it to complement or override searches in system-wide
+ * directories.
  *
  * If libcamera has been installed, the build directory path is not available
  * and this function returns an empty string.
@@ -385,6 +389,45 @@ std::string libcameraBuildPath()
 	return dirname(info.dli_fname) + "/../../";
 }
 
+/**
+ * \brief Retrieve the path to the source directory
+ *
+ * During development, it is useful to run libcamera binaries directly from the
+ * build directory without installing them. This function helps components that
+ * need to locate resources in the source tree, such as IPA configuration
+ * files, by providing them with the path to the root of the source directory.
+ * Callers can then use it to complement or override searches in system-wide
+ * directories.
+ *
+ * If libcamera has been installed, the source directory path is not available
+ * and this function returns an empty string.
+ *
+ * \return The path to the source directory if running from a build directory,
+ * or an empty string otherwise
+ */
+std::string libcameraSourcePath()
+{
+	std::string path = libcameraBuildPath();
+	if (path.empty())
+		return std::string();
+
+	path += "source";
+
+	char *real = realpath(path.c_str(), nullptr);
+	if (!real)
+		return std::string();
+
+	path = real;
+	free(real);
+
+	struct stat statbuf;
+	int ret = stat(path.c_str(), &statbuf);
+	if (ret < 0 || (statbuf.st_mode & S_IFMT) != S_IFDIR)
+		return std::string();
+
+	return path + "/";
+}
+
 } /* namespace utils */
 
 } /* namespace libcamera */