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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/*
* Copyright (C) 2019, Google Inc.
*
* file_descriptor.cpp - File descriptor wrapper
*/
#include <libcamera/file_descriptor.h>
#include <string.h>
#include <unistd.h>
#include <utility>
#include "libcamera/internal/log.h"
/**
* \file file_descriptor.h
* \brief File descriptor wrapper
*/
namespace libcamera {
LOG_DEFINE_CATEGORY(FileDescriptor)
/**
* \class FileDescriptor
* \brief RAII-style wrapper for file descriptors
*
* The FileDescriptor class provides RAII-style lifetime management of file
* descriptors with an efficient mechanism for ownership sharing. At its core,
* an internal Descriptor object wraps a file descriptor (expressed as a signed
* integer) with an RAII-style interface. The Descriptor is then implicitly
* shared with all FileDescriptor instances constructed as copies.
*
* When constructed from a numerical file descriptor, the FileDescriptor
* instance duplicates the file descriptor and wraps the duplicate as a
* Descriptor. The copy constructor and assignment operator create copies that
* share the Descriptor, while the move versions of those methods additionally
* make the other FileDescriptor invalid. When the last FileDescriptor that
* references a Descriptor is destroyed, the file descriptor is closed.
*
* The numerical file descriptor is available through the fd() method. As
* constructing a FileDescriptor from a numerical file descriptor duplicates
* the file descriptor, the value returned by fd() will be different than the
* value passed to the constructor. All FileDescriptor instances created as
* copies of a FileDescriptor will report the same fd() value. Callers can
* perform operations on the fd(), but shall never close it manually.
*/
/**
* \brief Create a FileDescriptor wrapping a copy of a given \a fd
* \param[in] fd File descriptor
*
* Constructing a FileDescriptor from a numerical file descriptor duplicates the
* \a fd and takes ownership of the copy. The original \a fd is left untouched,
* and the caller is responsible for closing it when appropriate. The duplicated
* file descriptor will be closed automatically when all FileDescriptor
* instances that reference it are destroyed.
*
* If the \a fd is negative, the FileDescriptor is constructed as invalid and
* the fd() method will return -1.
*/
FileDescriptor::FileDescriptor(int fd)
{
if (fd < 0)
return;
fd_ = std::make_shared<Descriptor>(fd);
if (fd_->fd() < 0)
fd_.reset();
}
/**
* \brief Copy constructor, create a FileDescriptor from a copy of \a other
* \param[in] other The other FileDescriptor
*
* Copying a FileDescriptor implicitly shares ownership of the wrapped file
* descriptor. The original FileDescriptor is left untouched, and the caller is
* responsible for destroying it when appropriate. The wrapped file descriptor
* will be closed automatically when all FileDescriptor instances that
* reference it are destroyed.
*/
FileDescriptor::FileDescriptor(const FileDescriptor &other)
: fd_(other.fd_)
{
}
/**
* \brief Move constructor, create a FileDescriptor by taking over \a other
* \param[in] other The other FileDescriptor
*
* Moving a FileDescriptor moves the reference to the wrapped descriptor owned
* by \a other to the new FileDescriptor. The \a other FileDescriptor is
* invalidated and its fd() method will return -1. The wrapped file descriptor
* will be closed automatically when all FileDescriptor instances that
* reference it are destroyed.
*/
FileDescriptor::FileDescriptor(FileDescriptor &&other)
: fd_(std::move(other.fd_))
{
}
/**
* \brief Destroy the FileDescriptor instance
*
* Destroying a FileDescriptor instance releases its reference to the wrapped
* descriptor, if any. When the last instance that references a wrapped
* descriptor is destroyed, the file descriptor is automatically closed.
*/
FileDescriptor::~FileDescriptor()
{
}
/**
* \brief Copy assignment operator, replace the wrapped file descriptor with a
* copy of \a other
* \param[in] other The other FileDescriptor
*
* Copying a FileDescriptor creates a new reference to the wrapped file
* descriptor owner by \a other. If \a other is invalid, *this will also be
* invalid. The original FileDescriptor is left untouched, and the caller is
* responsible for destroying it when appropriate. The wrapped file descriptor
* will be closed automatically when all FileDescriptor instances that
* reference it are destroyed.
*
* \return A reference to this FileDescriptor
*/
FileDescriptor &FileDescriptor::operator=(const FileDescriptor &other)
{
fd_ = other.fd_;
return *this;
}
/**
* \brief Move assignment operator, replace the wrapped file descriptor by
* taking over \a other
* \param[in] other The other FileDescriptor
*
* Moving a FileDescriptor moves the reference to the wrapped descriptor owned
* by \a other to the new FileDescriptor. If \a other is invalid, *this will
* also be invalid. The \a other FileDescriptor is invalidated and its fd()
* method will return -1. The wrapped file descriptor will be closed
* automatically when all FileDescriptor instances that reference it are
* destroyed.
*
* \return A reference to this FileDescriptor
*/
FileDescriptor &FileDescriptor::operator=(FileDescriptor &&other)
{
fd_ = std::move(other.fd_);
return *this;
}
/**
* \fn FileDescriptor::isValid()
* \brief Check if the FileDescriptor instance is valid
* \return True if the FileDescriptor is valid, false otherwise
*/
/**
* \fn FileDescriptor::fd()
* \brief Retrieve the numerical file descriptor
* \return The numerical file descriptor, which may be -1 if the FileDescriptor
* instance is invalid
*/
/**
* \brief Duplicate a FileDescriptor
*
* Duplicating a FileDescriptor creates a duplicate of the wrapped file
* descriptor and returns a new FileDescriptor instance that wraps the
* duplicate. The fd() method of the original and duplicate instances will
* return different values. The duplicate instance will not be affected by
* destruction of the original instance or its copies.
*
* \return A new FileDescriptor instance wrapping a duplicate of the original
* file descriptor
*/
FileDescriptor FileDescriptor::dup() const
{
return FileDescriptor(fd());
}
FileDescriptor::Descriptor::Descriptor(int fd)
{
/* Failing to dup() a fd should not happen and is fatal. */
fd_ = ::dup(fd);
if (fd_ == -1) {
int ret = -errno;
LOG(FileDescriptor, Fatal)
<< "Failed to dup() fd: " << strerror(-ret);
}
}
FileDescriptor::Descriptor::~Descriptor()
{
if (fd_ != -1)
close(fd_);
}
} /* namespace libcamera */
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