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).
Very bare-bones for now. Doesn't support arguments or environment (we don't have that stuff right now), and the executable is not a valid ELF, it terminates the task.
But it's a start!
If a section needs to be mapped at 0x50f50 and its size is 0x200, then that address space exceeds one page.
But since 0x200 is less than one page, we only map one page.
If we count the offset, 0xf50 + 0x200 need two pages. So we can map the right amount of memory.
We should start to drop the old InitRD API, which only allows for files to be loaded from the initrd, and which forces pathnames to be relative (bin/init)
With VFS, we can load any kind of file from any kind of filesystem, and using paths that make sense (/bin/init)
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.
The exit() libc function already accepted an integer, but didn't pass it on to the kernel since we had no mechanism for it to do that.
Now, the kernel stores a task's exit status to display it later (and in the future, return it to userspace via wait()/waitpid())
Kernel: Add an errno.h header with definitions for each header,
and return those, negated, from syscalls when there is an error.
mmap() returns an invalid address with errno encoded, instead of
returning a negated errno; this address is encoded as ffffffffffffffEE
where EE is errno in hex.
libc: make syscall() return -1 and set errno on error, instead of
returning the raw return value of the system call. Also, add mmap()
and munmap() wrappers in sys/mman.h :).
userspace: make the memeater program show the value of errno
when allocating memory fails.
Things to improve: add perror() and strerror() to make the errno
experience even better! >.<
This struct allows us to keep track of what memory is used by the loaded executable. For some reason, freeing this memory when the task exits triggers a kernel page fault, so I'm not doing that right now.
