1 files changed, 139 insertions, 0 deletions
diff --git a/src/libcamera/source_paths.cpp b/src/libcamera/source_paths.cpp
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+++ b/src/libcamera/source_paths.cpp
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+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Google Inc.
+ *
+ * source_paths.cpp - Identify libcamera source and build paths
+ */
+
+#include "libcamera/internal/source_paths.h"
+
+#include <dlfcn.h>
+#include <elf.h>
+#include <link.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include "libcamera/internal/utils.h"
+
+/**
+ * \file source_paths.h
+ * \brief Identify the build and source path of a not-yet-installed library
+ */
+
+/* musl doesn't declare _DYNAMIC in link.h, declare it manually. */
+extern ElfW(Dyn) _DYNAMIC[];
+
+namespace libcamera {
+
+namespace {
+
+/**
+ * \brief Check if libcamera is installed or not
+ *
+ * Utilise the build_rpath dynamic tag which is stripped out by meson at
+ * install time to determine at runtime if the library currently executing
+ * has been installed or not.
+ *
+ * \return True if libcamera is installed, false otherwise
+ */
+bool isLibcameraInstalled()
+{
+	/*
+	 * DT_RUNPATH (DT_RPATH when the linker uses old dtags) is removed on
+	 * install.
+	 */
+	for (const ElfW(Dyn) *dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn) {
+		if (dyn->d_tag == DT_RUNPATH || dyn->d_tag == DT_RPATH)
+			return false;
+	}
+
+	return true;
+}
+
+} /* namespace */
+
+namespace utils {
+
+/**
+ * \brief Retrieve the path to the build 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 build tree, such as IPA modules or IPA proxy
+ * workers, by providing them with the path to the root of the build directory.
+ * 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.
+ *
+ * \return The path to the build directory if running from a build, or an empty
+ * string otherwise
+ */
+std::string libcameraBuildPath()
+{
+	if (isLibcameraInstalled())
+		return std::string();
+
+	Dl_info info;
+
+	/* Look up our own symbol. */
+	int ret = dladdr(reinterpret_cast<void *>(libcameraBuildPath), &info);
+	if (ret == 0)
+		return std::string();
+
+	std::string path = dirname(info.dli_fname) + "/../../";
+
+	char *real = realpath(path.c_str(), nullptr);
+	if (!real)
+		return std::string();
+
+	path = real;
+	free(real);
+
+	return path + "/";
+}
+
+/**
+ * \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 */