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libcamera: shared_mem_object: Reorganize the code and document the SharedMemObject class

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The SharedMemObject class template contains a fair amount of inline code
that does not depend on the template types T. To avoid duplicating it in
every template specialization, split that code to a separate base
SharedMem class.

We don't define copy semantics for the classes (we don't need one at the
moment) and we make them non-copyable since the default copy constructor
would lead to use-after-unmap.

Doxygen documentation by Dennis Bonke and Andrei Konovalov.

Reviewed-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Milan Zamazal <mzamazal@redhat.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Co-developed-by: Dennis Bonke <admin@dennisbonke.com>
Signed-off-by: Dennis Bonke <admin@dennisbonke.com>
Signed-off-by: Andrei Konovalov <andrey.konovalov.ynk@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
This commit is contained in:
Andrei Konovalov 2024-04-16 11:13:42 +02:00 • committed by Kieran Bingham
parent ce3c8a5082
commit 9a2d7d3b6a
3 changed files with 290 additions and 50 deletions
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103
include/libcamera/internal/shared_mem_object.h
View file

@ -1,85 +1,98 @@
/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* Copyright (C) 2023, Raspberry Pi Ltd
* Copyright (C) 2023 Raspberry Pi Ltd
* Copyright (C) 2024 Andrei Konovalov
* Copyright (C) 2024 Dennis Bonke
*
* shared_mem_object.h - Helper class for shared memory allocations
* shared_mem_object.h - Helpers for shared memory allocations
*/
#pragma once
#include <fcntl.h>
#include <stddef.h>
#include <stdint.h>
#include <string>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>
#include <type_traits>
#include <utility>
#include <libcamera/base/class.h>
#include <libcamera/base/shared_fd.h>
#include <libcamera/base/span.h>
namespace libcamera {
template<class T>
class SharedMemObject
class SharedMem
{
public:
SharedMem();
SharedMem(const std::string &name, std::size_t size);
SharedMem(SharedMem &&rhs);
virtual ~SharedMem();
SharedMem &operator=(SharedMem &&rhs);
const SharedFD &fd() const
{
return fd_;
}
Span<uint8_t> mem() const
{
return mem_;
}
explicit operator bool() const
{
return !mem_.empty();
}
private:
LIBCAMERA_DISABLE_COPY(SharedMem)
SharedFD fd_;
Span<uint8_t> mem_;
};
template<class T, typename = std::enable_if_t<std::is_standard_layout<T>::value>>
class SharedMemObject : public SharedMem
{
public:
static constexpr std::size_t kSize = sizeof(T);
SharedMemObject()
: obj_(nullptr)
: SharedMem(), obj_(nullptr)
{
}
template<class... Args>
SharedMemObject(const std::string &name, Args &&...args)
: name_(name), obj_(nullptr)
: SharedMem(name, kSize), obj_(nullptr)
{
void *mem;
int ret;
ret = memfd_create(name_.c_str(), MFD_CLOEXEC);
if (ret < 0)
if (mem().empty())
return;
fd_ = SharedFD(std::move(ret));
if (!fd_.isValid())
return;
ret = ftruncate(fd_.get(), kSize);
if (ret < 0)
return;
mem = mmap(nullptr, kSize, PROT_READ | PROT_WRITE, MAP_SHARED,
fd_.get(), 0);
if (mem == MAP_FAILED)
return;
obj_ = new (mem) T(std::forward<Args>(args)...);
obj_ = new (mem().data()) T(std::forward<Args>(args)...);
}
SharedMemObject(SharedMemObject<T> &&rhs)
: SharedMem(std::move(rhs))
{
this->name_ = std::move(rhs.name_);
this->fd_ = std::move(rhs.fd_);
this->obj_ = rhs.obj_;
rhs.obj_ = nullptr;
}
~SharedMemObject()
{
if (obj_) {
if (obj_)
obj_->~T();
munmap(obj_, kSize);
}
}
/* Make SharedMemObject non-copyable for now. */
LIBCAMERA_DISABLE_COPY(SharedMemObject)
SharedMemObject<T> &operator=(SharedMemObject<T> &&rhs)
{
this->name_ = std::move(rhs.name_);
this->fd_ = std::move(rhs.fd_);
SharedMem::operator=(std::move(rhs));
this->obj_ = rhs.obj_;
rhs.obj_ = nullptr;
return *this;
@ -105,19 +118,9 @@ public:
return *obj_;
}
const SharedFD &fd() const
{
return fd_;
}
explicit operator bool() const
{
return !!obj_;
}
private:
std::string name_;
SharedFD fd_;
LIBCAMERA_DISABLE_COPY(SharedMemObject)
T *obj_;
};