That will probably happen a lot. We want userspace to tell us IF THE ERROR IS RELEVANT.
So, these unnecessary warnings are just noise.
Userspace may also use these functions to check for file descriptors.
For example, libc does this at program initialization, it checks whether fd 0 and 1 exist (by calling lseek() and seeing if it fails with errno=EBADF).
Kernel: Implement a descriptor struct which stores the opened node and read offset, and give each task 8 of those.
Implement three syscalls: sys_read, sys_open and sys_close (sys_write still writes to the console instead of using a fd, for now)
Implement three new errors: ENOENT, EBADF and EMFILE.
libc: Implement the new errors, and the new syscalls in syscall().
Also fix _RETURN_WITH_ERRNO() to set errno correctly, which was making strerror() return null, thus crashing perror().
userspace: make init demonstrate the new file API.
