v4l2: compat_manager: Move file operations to new struct FileOperations

Create a new FileOperations structure to hold all the dynamically-loaded
C library file operations. The file operations are now exposed publicly,
to prepare for usage of mmap in the V4L2CameraProxy.

A new template helper function is added to retrieve a symbol with
dlsym() with proper casting to simplify the V4L2CompatManager
constructor.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/v4l2/v4l2_compat_manager.cpp

@@ -28,15 +28,23 @@ using namespace libcamera;
 
 LOG_DEFINE_CATEGORY(V4L2Compat)
 
+namespace {
+template<typename T>
+void get_symbol(T &func, const char *name)
+{
+	func = reinterpret_cast<T>(dlsym(RTLD_NEXT, name));
+}
+} /* namespace */
+
 V4L2CompatManager::V4L2CompatManager()
 	: cm_(nullptr), initialized_(false)
 {
-	openat_func_ = (openat_func_t)dlsym(RTLD_NEXT, "openat");
-	dup_func_    = (dup_func_t   )dlsym(RTLD_NEXT, "dup");
-	close_func_  = (close_func_t )dlsym(RTLD_NEXT, "close");
-	ioctl_func_  = (ioctl_func_t )dlsym(RTLD_NEXT, "ioctl");
-	mmap_func_   = (mmap_func_t  )dlsym(RTLD_NEXT, "mmap");
-	munmap_func_ = (munmap_func_t)dlsym(RTLD_NEXT, "munmap");
+	get_symbol(fops_.openat, "openat");
+	get_symbol(fops_.dup, "dup");
+	get_symbol(fops_.close, "close");
+	get_symbol(fops_.ioctl, "ioctl");
+	get_symbol(fops_.mmap, "mmap");
+	get_symbol(fops_.munmap, "munmap");
 }
 
 V4L2CompatManager::~V4L2CompatManager()
@@ -141,7 +149,7 @@ int V4L2CompatManager::getCameraIndex(int fd)
 
 int V4L2CompatManager::openat(int dirfd, const char *path, int oflag, mode_t mode)
 {
-	int fd = openat_func_(dirfd, path, oflag, mode);
+	int fd = fops_.openat(dirfd, path, oflag, mode);
 	if (fd < 0)
 		return fd;
 
@@ -160,7 +168,7 @@ int V4L2CompatManager::openat(int dirfd, const char *path, int oflag, mode_t mod
 		return fd;
 	}
 
-	close_func_(fd);
+	fops_.close(fd);
 
 	unsigned int camera_index = static_cast<unsigned int>(ret);
 
@@ -182,7 +190,7 @@ int V4L2CompatManager::openat(int dirfd, const char *path, int oflag, mode_t mod
 
 int V4L2CompatManager::dup(int oldfd)
 {
-	int newfd = dup_func_(oldfd);
+	int newfd = fops_.dup(oldfd);
 	if (newfd < 0)
 		return newfd;
 
@@ -205,7 +213,7 @@ int V4L2CompatManager::close(int fd)
 		return 0;
 	}
 
-	return close_func_(fd);
+	return fops_.close(fd);
 }
 
 void *V4L2CompatManager::mmap(void *addr, size_t length, int prot, int flags,
@@ -213,7 +221,7 @@ void *V4L2CompatManager::mmap(void *addr, size_t length, int prot, int flags,
 {
 	V4L2CameraProxy *proxy = getProxy(fd);
 	if (!proxy)
-		return mmap_func_(addr, length, prot, flags, fd, offset);
+		return fops_.mmap(addr, length, prot, flags, fd, offset);
 
 	void *map = proxy->mmap(length, prot, flags, offset);
 	if (map == MAP_FAILED)
@@ -227,7 +235,7 @@ int V4L2CompatManager::munmap(void *addr, size_t length)
 {
 	auto device = mmaps_.find(addr);
 	if (device == mmaps_.end())
-		return munmap_func_(addr, length);
+		return fops_.munmap(addr, length);
 
 	V4L2CameraProxy *proxy = device->second;
 
@@ -244,7 +252,7 @@ int V4L2CompatManager::ioctl(int fd, unsigned long request, void *arg)
 {
 	V4L2CameraProxy *proxy = getProxy(fd);
 	if (!proxy)
-		return ioctl_func_(fd, request, arg);
+		return fops_.ioctl(fd, request, arg);
 
 	return proxy->ioctl(request, arg);
 }

src/v4l2/v4l2_compat_manager.h

@@ -26,11 +26,30 @@ using namespace libcamera;
 class V4L2CompatManager : public Thread
 {
 public:
+	struct FileOperations {
+		using openat_func_t = int (*)(int dirfd, const char *path,
+					      int oflag, ...);
+		using dup_func_t = int (*)(int oldfd);
+		using close_func_t = int (*)(int fd);
+		using ioctl_func_t = int (*)(int fd, unsigned long request, ...);
+		using mmap_func_t = void *(*)(void *addr, size_t length, int prot,
+					      int flags, int fd, off_t offset);
+		using munmap_func_t = int (*)(void *addr, size_t length);
+
+		openat_func_t openat;
+		dup_func_t dup;
+		close_func_t close;
+		ioctl_func_t ioctl;
+		mmap_func_t mmap;
+		munmap_func_t munmap;
+	};
+
 	static V4L2CompatManager *instance();
 
 	int init();
 
 	V4L2CameraProxy *getProxy(int fd);
+	const FileOperations &fops() const { return fops_; }
 
 	int openat(int dirfd, const char *path, int oflag, mode_t mode);
 
@@ -48,20 +67,7 @@ private:
 	void run() override;
 	int getCameraIndex(int fd);
 
-	typedef int (*openat_func_t)(int dirfd, const char *path, int oflag, ...);
-	typedef int (*dup_func_t)(int oldfd);
-	typedef int (*close_func_t)(int fd);
-	typedef int (*ioctl_func_t)(int fd, unsigned long request, ...);
-	typedef void *(*mmap_func_t)(void *addr, size_t length, int prot,
-				     int flags, int fd, off_t offset);
-	typedef int (*munmap_func_t)(void *addr, size_t length);
-
-	openat_func_t openat_func_;
-	dup_func_t    dup_func_;
-	close_func_t  close_func_;
-	ioctl_func_t  ioctl_func_;
-	mmap_func_t   mmap_func_;
-	munmap_func_t munmap_func_;
+	FileOperations fops_;
 
 	CameraManager *cm_;