Function put_page_chunk

kernel/src/memory.rs:603–643

Finds an available page chunk entry, stores the physical address in the page table and returns the virtual address.

(
    level_4_physaddr: u64,
    physaddr: PhysAddr
)

/// Finds an available page chunk entry, stores the physical address
/// in the page table and returns the virtual address.
pub fn put_page_chunk(
    level_4_physaddr: u64,
    physaddr: PhysAddr
) -> Result<VirtAddr, usize> {
    let memory_info = unsafe {MEMORY_INFO.as_mut().unwrap()};

    let l4_table: &mut PageTable = unsafe {
        &mut *(memory_info.physical_memory_offset
               + level_4_physaddr).as_mut_ptr()};
    let l4_entry = &mut l4_table[MEMORY_CHUNK_L4_ENTRY];

    if l4_entry.is_unused() {
        // L3 table not allocated -> Create
        let (_new_table_ptr, new_table_physaddr) = create_empty_pagetable();
        l4_entry.set_addr(PhysAddr::new(new_table_physaddr),
                          PageTableFlags::PRESENT |
                          PageTableFlags::WRITABLE |
                          PageTableFlags::USER_ACCESSIBLE);
    }
    let l3_table: &mut PageTable = unsafe {
        &mut *(memory_info.physical_memory_offset
               + l4_entry.addr().as_u64()).as_mut_ptr()};

    // Each entry in l3_table from FIRST to LAST inclusive
    // is a separate chunk
    for ind in MEMORY_CHUNK_L3_FIRST..=MEMORY_CHUNK_L3_LAST {
        let entry = &mut l3_table[ind];
        if entry.is_unused() {
            // Found an empty chunk
            entry.set_addr(physaddr,
                           PageTableFlags::PRESENT |
                           PageTableFlags::WRITABLE |
                           PageTableFlags::USER_ACCESSIBLE);

            // Convert L4 and L3 index into virtual address
            return Ok(VirtAddr::new(((MEMORY_CHUNK_L4_ENTRY as u64) << 39) |
                                    (ind << 30) as u64));
        }
    }
    Err(syscalls::SYSCALL_ERROR_NOMEMSLOTS)
}

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