#include "errno.h"
#include "globals.h"
#include "mm/mm.h"
#include "util/debug.h"

#include "mm/mman.h"

/*
 * This function implements the brk(2) system call.
 *
 * This routine manages the calling process's "break" -- the ending address
 * of the process's dynamic region (heap)
 *
 * Some important details on the range of values 'p_brk' can take:
 * 1) 'p_brk' should not be set to a value lower than 'p_start_brk', since this
 *    could overrite data in another memory region. But, 'p_brk' can be equal to
 *    'p_start_brk', which would mean that there is no heap yet/is empty.
 * 2) Growth of the 'p_brk' cannot overlap with/expand into an existing
 *    mapping. Use vmmap_is_range_empty() to help with this.
 * 3) 'p_brk' cannot go beyond the region of the address space allocated for use by
 *    userland (USER_MEM_HIGH)
 *
 * Before setting 'p_brk' to 'addr', you must account for all scenarios by comparing
 * the page numbers of addr, 'p_brk' and 'p_start_brk' as the vmarea that represents the heap
 * has page granularity. Think about the following sub-cases (note that the heap 
 * should always be represented by at most one vmarea):
 * 1) The heap needs to be created. What permissions and attributes does a process
 *    expect the heap to have?
 * 2) The heap already exists, so you need to modify its end appropriately.
 * 3) The heap needs to shrink.
 *
 * Beware of page alignment!:
 * 1) The starting break is not necessarily page aligned. Since the loader sets
 *    'p_start_brk' to be the end of the bss section, 'p_start_brk' should always be
 *    aligned up to start the dynamic region at the first page after bss_end.
 * 2) vmareas only have page granularity, so you will need to take this
 *    into account when deciding how to set the mappings if p_brk or p_start_brk
 *    is not page aligned. The caller of do_brk() would be very disappointed if
 *    you give them less than they asked for!
 *
 * Some additional details:
 * 1) You are guaranteed that the process data/bss region is non-empty.
 *    That is, if the starting brk is not page-aligned, its page has
 *    read/write permissions.
 * 2) If 'addr' is NULL, you should return the current break. We use this to
 *    implement sbrk(0) without writing a separate syscall. Look in
 *    user/libc/syscall.c if you're curious.
 * 3) Return 0 on success, -errno on failure. The 'ret' argument should be used to 
 *    return the updated 'p_brk' on success.
 *
 * Error cases do_brk is responsible for generating:
 *  - ENOMEM: attempting to set p_brk beyond its valid range
 */
long do_brk(void *addr, void **ret)
{
    NOT_YET_IMPLEMENTED("VM: ***none***");
    return 0;
}