libcamera: base: Add MemFd helper class

libcamera creates memfds in two locations already, duplicating some
code. Move the code to a new MemFd helper class.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Milan Zamazal <mzamazal@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

include/libcamera/base/memfd.h

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Ideas on Board Oy
+ *
+ * Anonymous file creation
+ */
+
+#pragma once
+
+#include <stddef.h>
+
+#include <libcamera/base/flags.h>
+#include <libcamera/base/unique_fd.h>
+
+namespace libcamera {
+
+class MemFd
+{
+public:
+	enum class Seal {
+		None = 0,
+		Shrink = (1 << 0),
+		Grow = (1 << 1),
+	};
+
+	using Seals = Flags<Seal>;
+
+	static UniqueFD create(const char *name, std::size_t size,
+			       Seals seals = Seal::None);
+};
+
+LIBCAMERA_FLAGS_ENABLE_OPERATORS(MemFd::Seal)
+
+} /* namespace libcamera */

include/libcamera/base/meson.build

@@ -21,6 +21,7 @@ libcamera_base_private_headers = files([
     'event_notifier.h',
     'file.h',
     'log.h',
+    'memfd.h',
     'message.h',
     'mutex.h',
     'private.h',

src/libcamera/base/memfd.cpp

@@ -0,0 +1,116 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2024, Ideas on Board Oy
+ *
+ * Anonymous file creation
+ */
+
+#include <libcamera/base/memfd.h>
+
+#include <fcntl.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include <libcamera/base/log.h>
+
+/**
+ * \file base/memfd.h
+ * \brief Anonymous file creation
+ */
+
+/* uClibc doesn't provide the file sealing API. */
+#ifndef __DOXYGEN__
+#if not HAVE_FILE_SEALS
+#define F_ADD_SEALS		1033
+#define F_SEAL_SHRINK		0x0002
+#define F_SEAL_GROW		0x0004
+#endif
+#endif
+
+namespace libcamera {
+
+LOG_DECLARE_CATEGORY(File)
+
+/**
+ * \class MemFd
+ * \brief Helper class to create anonymous files
+ *
+ * Anonymous files behave like regular files, and can be modified, truncated,
+ * memory-mapped and so on. Unlike regular files, they however live in RAM and
+ * don't have permanent backing storage.
+ */
+
+/**
+ * \enum MemFd::Seal
+ * \brief Seals for the MemFd::create() function
+ * \var MemFd::Seal::None
+ * \brief No seals (used as default value)
+ * \var MemFd::Seal::Shrink
+ * \brief Prevent the memfd from shrinking
+ * \var MemFd::Seal::Grow
+ * \brief Prevent the memfd from growing
+ */
+
+/**
+ * \typedef MemFd::Seals
+ * \brief A bitwise combination of MemFd::Seal values
+ */
+
+/**
+ * \brief Create an anonymous file
+ * \param[in] name The file name (displayed in symbolic links in /proc/self/fd/)
+ * \param[in] size The file size
+ * \param[in] seals The file seals
+ *
+ * This function is a helper that wraps anonymous file (memfd) creation and
+ * sets the file size and optional seals.
+ *
+ * \return The descriptor of the anonymous file if creation succeeded, or an
+ * invalid UniqueFD otherwise
+ */
+UniqueFD MemFd::create(const char *name, std::size_t size, Seals seals)
+{
+#if HAVE_MEMFD_CREATE
+	int ret = memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
+#else
+	int ret = syscall(SYS_memfd_create, name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
+#endif
+	if (ret < 0) {
+		ret = errno;
+		LOG(File, Error)
+			<< "Failed to allocate memfd storage for " << name
+			<< ": " << strerror(ret);
+		return {};
+	}
+
+	UniqueFD memfd(ret);
+
+	ret = ftruncate(memfd.get(), size);
+	if (ret < 0) {
+		ret = errno;
+		LOG(File, Error)
+			<< "Failed to set memfd size for " << name
+			<< ": " << strerror(ret);
+		return {};
+	}
+
+	if (seals) {
+		int fileSeals = (seals & Seal::Shrink ? F_SEAL_SHRINK : 0)
+			      | (seals & Seal::Grow ? F_SEAL_GROW : 0);
+
+		ret = fcntl(memfd.get(), F_ADD_SEALS, fileSeals);
+		if (ret < 0) {
+			ret = errno;
+			LOG(File, Error)
+				<< "Failed to seal the memfd for " << name
+				<< ": " << strerror(ret);
+			return {};
+		}
+	}
+
+	return memfd;
+}
+
+} /* namespace libcamera */

src/libcamera/base/meson.build

@@ -10,6 +10,7 @@ libcamera_base_sources = files([
     'file.cpp',
     'flags.cpp',
     'log.cpp',
+    'memfd.cpp',
     'message.cpp',
     'mutex.cpp',
     'object.cpp',

src/libcamera/dma_buf_allocator.cpp

@@ -13,7 +13,6 @@
 #include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
-#include <sys/syscall.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -22,6 +21,7 @@
 #include <linux/udmabuf.h>
 
 #include <libcamera/base/log.h>
+#include <libcamera/base/memfd.h>
 
 /**
  * \file dma_buf_allocator.cpp
@@ -126,54 +126,16 @@ DmaBufAllocator::~DmaBufAllocator() = default;
  * \brief Check if the DmaBufAllocator instance is valid
  * \return True if the DmaBufAllocator is valid, false otherwise
  */
-
-/* uClibc doesn't provide the file sealing API. */
-#ifndef __DOXYGEN__
-#if not HAVE_FILE_SEALS
-#define F_ADD_SEALS		1033
-#define F_SEAL_SHRINK		0x0002
-#endif
-#endif
-
 UniqueFD DmaBufAllocator::allocFromUDmaBuf(const char *name, std::size_t size)
 {
 	/* Size must be a multiple of the page size. Round it up. */
 	std::size_t pageMask = sysconf(_SC_PAGESIZE) - 1;
 	size = (size + pageMask) & ~pageMask;
 
-#if HAVE_MEMFD_CREATE
-	int ret = memfd_create(name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
-#else
-	int ret = syscall(SYS_memfd_create, name, MFD_ALLOW_SEALING | MFD_CLOEXEC);
-#endif
-	if (ret < 0) {
-		ret = errno;
-		LOG(DmaBufAllocator, Error)
-			<< "Failed to allocate memfd storage for " << name
-			<< ": " << strerror(ret);
-		return {};
-	}
-
-	UniqueFD memfd(ret);
-
-	ret = ftruncate(memfd.get(), size);
-	if (ret < 0) {
-		ret = errno;
-		LOG(DmaBufAllocator, Error)
-			<< "Failed to set memfd size for " << name
-			<< ": " << strerror(ret);
-		return {};
-	}
-
 	/* udmabuf dma-buffers *must* have the F_SEAL_SHRINK seal. */
-	ret = fcntl(memfd.get(), F_ADD_SEALS, F_SEAL_SHRINK);
+	UniqueFD memfd = MemFd::create(name, size, MemFd::Seal::Shrink);
-	if (ret < 0) {
+	if (!memfd.isValid())
-		ret = errno;
-		LOG(DmaBufAllocator, Error)
-			<< "Failed to seal the memfd for " << name
-			<< ": " << strerror(ret);
 		return {};
-	}
 
 	struct udmabuf_create create;
 
@@ -182,7 +144,7 @@ UniqueFD DmaBufAllocator::allocFromUDmaBuf(const char *name, std::size_t size)
 	create.offset = 0;
 	create.size = size;
 
-	ret = ::ioctl(providerHandle_.get(), UDMABUF_CREATE, &create);
+	int ret = ::ioctl(providerHandle_.get(), UDMABUF_CREATE, &create);
 	if (ret < 0) {
 		ret = errno;
 		LOG(DmaBufAllocator, Error)

src/libcamera/shared_mem_object.cpp

@@ -13,9 +13,9 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <sys/mman.h>
-#include <sys/syscall.h>
 #include <sys/types.h>
-#include <unistd.h>
+
+#include <libcamera/base/memfd.h>
 
 /**
  * \file shared_mem_object.cpp
@@ -58,22 +58,11 @@ SharedMem::SharedMem() = default;
  */
 SharedMem::SharedMem(const std::string &name, std::size_t size)
 {
-#if HAVE_MEMFD_CREATE
+	UniqueFD memfd = MemFd::create(name.c_str(), size);
-	int fd = memfd_create(name.c_str(), MFD_CLOEXEC);
+	if (!memfd.isValid())
-#else
-	int fd = syscall(SYS_memfd_create, name.c_str(), MFD_CLOEXEC);
-#endif
-	if (fd < 0)
 		return;
 
-	fd_ = SharedFD(std::move(fd));
+	fd_ = SharedFD(std::move(memfd));
-	if (!fd_.isValid())
-		return;
-
-	if (ftruncate(fd_.get(), size) < 0) {
-		fd_ = SharedFD();
-		return;
-	}
 
 	void *mem = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_SHARED,
 			 fd_.get(), 0);