Error when reading from Linux FIFO - linux

Question

In the embedded application I'm working on we have a serial port abstraction, and I'm currently working on a simulated variant of said abstraction to use when you are not running on the 'real' hardware. I'm using FIFO files for this, as you can then plug in whathever software you want to communicate with the actual application but I'm having trouble with the "read" function, which flags that you gave it an invalid fd. Though I have used debugging tools to verify that the fd passed to it is the same as has been opened earlier so it should be valid. I cannot find any cause for this problem.
FIFO files are opened through this function:
int createOpenFifo(const std::string& path, int flags)
{
int fd = open(path.c_str(), flags);
if (fd < 0)
{
mkfifo(path.c_str(), 0777);
fd = open(path.c_str(), flags);
if (fd < 0)
{
return -1;
}
}
return fd;
}
And the FIFOs are then written to using the following function:
int write_serial(handle_t handle, size_t length, const uint8_t* pData)
{
SerialFifoData* data = static_cast<SerialFifoData*>(handle);
size_t written = 0;
while (written < length)
{
int result = write(data->writeFd, pData + written, length - written);
if (result < 0)
{
return -1;
}
written += result;
}
return 0;
}
And finally read from using this function:
int read_serial(handle_t handle, size_t buffer_size, uint8_t* pBuffer, size_t* bytes_read)
{
SerialFifoData* data = static_cast<SerialFifoData*>(handle);
int return_val = read(data->readFd, pBuffer, buffer_size);
if (return_val < 0)
{
if (errno == EAGAIN || errno == EWOULDBLOCK) // Non-blocking, no data
// which flag is raised
// varies between POSIX
// implementations
{
*bytes_read = 0;
return -2;
}
return -1;
}
*bytes_read = return_val;
return 0;
}
I have verified that each function recieves correct input, and the read and write calls are nearly identical to those used for the actual serial port code (the only difference is how the FD is extracted from the handle) where they work just fine.