How can you flush a write using a file descriptor?

Question

It turns out this whole misunderstanding of the open() versus fopen() stems from a buggy I2C driver in the Linux 2.6.14 kernel on an ARM. Backporting a worki

Answer 1

fflush() only flushes the buffering added by the stdio fopen() layer, as managed by the FILE * object. The underlying file itself, as seen by the kernel, is not buffered at this level. This means that writes that bypass the FILE * layer, using fileno() and a raw write(), are also not buffered in a way that fflush() would flush.

As others have pointed out, try not mixing the two. If you need to use "raw" I/O functions such as ioctl(), then open() the file yourself directly, without using fopen<() and friends from stdio.