V4L2Loader.hpp

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#pragma once
 
#include <ossia/detail/dylib_loader.hpp>
 
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <unistd.h>
 
#include <cerrno>
 
// libv4l2.h is not always installed even where the library is, so the three
// entry points we use are declared here rather than included.
extern "C" {
int v4l2_open(const char* file, int oflag, ...);
int v4l2_close(int fd);
int v4l2_dup(int fd);
int v4l2_ioctl(int fd, unsigned long int request, ...);
ssize_t v4l2_read(int fd, void* buffer, size_t n);
ssize_t v4l2_write(int fd, const void* buffer, size_t n);
void* v4l2_mmap(void* start, size_t length, int prot, int flags, int fd, int64_t offset);
int v4l2_munmap(void* _start, size_t length);
}
 
namespace score::gfx::v4l2
{
 
class Libv4l2
{
public:
  decltype(&::v4l2_open) open{};
  decltype(&::v4l2_close) close{};
  decltype(&::v4l2_ioctl) ioctl{};
 
  bool available() const noexcept { return open && close && ioctl; }
 
  static const Libv4l2& instance()
  {
    static const Libv4l2 self;
    return self;
  }
 
private:
  Libv4l2()
      : library("libv4l2.so.0")
  {
    open = library.symbol<decltype(&::v4l2_open)>("v4l2_open");
    close = library.symbol<decltype(&::v4l2_close)>("v4l2_close");
    ioctl = library.symbol<decltype(&::v4l2_ioctl)>("v4l2_ioctl");
  }
 
  ossia::dylib_loader library;
};
 
inline int retryIoctl(int fd, unsigned long request, void* arg) noexcept
{
  const auto& lib = Libv4l2::instance();
  int r;
  do
  {
    r = lib.available() ? lib.ioctl(fd, request, arg) : ::ioctl(fd, request, arg);
  } while(r == -1 && errno == EINTR);
  return r;
}
 
inline int openDeviceRaw(const char* path, int flags) noexcept
{
  return ::open(path, flags);
}
 
inline void closeDeviceRaw(int fd) noexcept
{
  ::close(fd);
}
 
inline int retryIoctlRaw(int fd, unsigned long request, void* arg) noexcept
{
  int r;
  do
  {
    r = ::ioctl(fd, request, arg);
  } while(r == -1 && errno == EINTR);
  return r;
}
 
inline int openDevice(const char* path, int flags) noexcept
{
  const auto& lib = Libv4l2::instance();
  return lib.available() ? lib.open(path, flags) : ::open(path, flags);
}
 
inline void closeDevice(int fd) noexcept
{
  const auto& lib = Libv4l2::instance();
  if(lib.available())
    lib.close(fd);
  else
    ::close(fd);
}
 
} // namespace score::gfx::v4l2