[libcamera-devel] [PATCH 03/20] pipeline: rpi: Add SharedMemObject class

[Jacopo Mondi]

Cc-ing Andrey, Bryan and Hans for the SoftISP work

On Fri, Oct 06, 2023 at 02:19:43PM +0100, Naushir Patuck via libcamera-devel wrote:
> Add new SharedMemObject class that wraps a memfd memory allocation and
> constructs a templated object in the memory. With appropriate locking,
> this object can then be shared across different processes using the
> associated allocation file handle.
>
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> Reviewed-by: David Plowman <david.plowman at raspberrypi.com>
> ---
>  .../pipeline/rpi/common/shared_mem_object.h   | 118 ++++++++++++++++++
>  1 file changed, 118 insertions(+)
>  create mode 100644 src/libcamera/pipeline/rpi/common/shared_mem_object.h
>
> diff --git a/src/libcamera/pipeline/rpi/common/shared_mem_object.h b/src/libcamera/pipeline/rpi/common/shared_mem_object.h
> new file mode 100644
> index 000000000000..69051ecc3f52
> --- /dev/null
> +++ b/src/libcamera/pipeline/rpi/common/shared_mem_object.h
> @@ -0,0 +1,118 @@
> +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> +/*
> + * Copyright (C) 2023, Raspberry Pi Ltd
> + *
> + * shared_mem_object.h - Helper class for shared memory allocations
> + */
> +#pragma once
> +
> +#include <fcntl.h>
> +#include <string>
> +#include <sys/mman.h>
> +#include <sys/stat.h>
> +#include <unistd.h>

#include <utility> for std::forward

> +
> +#include <libcamera/base/class.h>
> +#include <libcamera/base/shared_fd.h>
> +
> +namespace libcamera {
> +
> +namespace RPi {
> +
> +template<class T>
> +class SharedMemObject
> +{
> +public:
> +	static constexpr std::size_t SIZE = sizeof(T);

and <cstddef> for std::size_t ?

> +
> +	SharedMemObject()
> +		: obj_(nullptr)
> +	{
> +	}
> +
> +	template<class... Args>
> +	SharedMemObject(const std::string &name, Args &&...args)
> +		: name_(name), obj_(nullptr)
> +	{
> +		void *mem;
> +		int ret;
> +
> +		ret = memfd_create(name_.c_str(), MFD_CLOEXEC);
> +		if (ret < 0)
> +			return;
> +
> +		fd_ = SharedFD(std::move(ret));
> +		if (!fd_.isValid())
> +			return;
> +
> +		ret = ftruncate(fd_.get(), SIZE);
> +		if (ret < 0)
> +			return;
> +
> +		mem = mmap(nullptr, SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,
> +			   fd_.get(), 0);
> +		if (mem == MAP_FAILED)
> +			return;
> +
> +		obj_ = new (mem) T(std::forward<Args>(args)...);
> +	}
> +
> +	~SharedMemObject()
> +	{
> +		if (obj_) {
> +			obj_->~T();
> +			munmap(obj_, SIZE);
> +		}
> +	}
> +
> +	/* Make SharedMemObject non-copyable for now. */
> +	LIBCAMERA_DISABLE_COPY(SharedMemObject)
> +
> +	SharedMemObject<T> &operator=(SharedMemObject<T> &&rhs)

Do you need a move constructor as well, since you have a move
assignment operator ?

	SharedMemObject(SharedMemObject<T> &&rhs)
	{
		this->name_ = std::move(rhs.name_);
		this->fd_ = std::move(rhs.fd_);
		this->obj_ = rhs.obj_;
		rhs.obj_ = nullptr;
	}


> +		this->name_ = std::move(rhs.name_);
> +		this->fd_ = std::move(rhs.fd_);
> +		this->obj_ = rhs.obj_;
> +		rhs.obj_ = nullptr;
> +		return *this;
> +	}
> +
> +	T *operator->()
> +	{
> +		return obj_;
> +	}
> +
> +	const T *operator->() const
> +	{
> +		return obj_;
> +	}
> +
> +	T &operator*()
> +	{
> +		return *obj_;
> +	}
> +
> +	const T &operator*() const
> +	{
> +		return *obj_;
> +	}
> +
> +	const SharedFD &fd() const
> +	{
> +		return fd_;
> +	}
> +
> +	explicit operator bool() const
> +	{
> +		return !!obj_;
> +	}
> +
> +private:
> +	std::string name_;
> +	SharedFD fd_;
> +	T *obj_;
> +};

The rest looks good.. making this a library component on top shouldn't be
hard..

Reviewed-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>

> +
> +} /* namespace RPi */
> +
> +} /* namespace libcamera */
> --
> 2.34.1
>