apio
e5cf32c7b3
Some pages, such as framebuffer pages, are not physical memory frames reserved for the current process. Some, such as the framebuffer, may be shared between all processes. Yet, on exit() or on exec(), a process frees all frames mapped into its address spaces. And on fork(), it copies all data between frames. So how could we map framebuffers. Simple: we use one of the bits in page table entries which are available to the OS, and mark whether that page is owned by the current process. If it is owned, it will be: - Freed on address space destruction - Its data will be copied to a new page owned by the child process on fork() If it is not owned, it will be: - Left alone on address space destruction - On fork(), the child's virtual page will be mapped to the same physical frame as the parent This still needs a bit more work, such as keeping a reference of how many processes use a page to free it when all processes using it exit/exec. This should be done for MAP_SHARED mappings, for example, since they are not permanent forever, unlike the framebuffer for example.
37 lines
1.1 KiB
C++
37 lines
1.1 KiB
C++
#pragma once
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#include <stdint.h>
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#ifndef PAGE_SIZE
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#define PAGE_SIZE 4096
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#endif
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#define MAP_READ_WRITE 1 << 0
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#define MAP_USER 1 << 1
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#define MAP_EXEC 1 << 2
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#define MAP_AS_OWNED_BY_TASK 1 << 3
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namespace MemoryManager
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{
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void init();
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void protect_kernel_sections();
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void* get_mapping(void* physicalAddress, int flags = MAP_READ_WRITE);
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void release_mapping(void* mapping);
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void* get_unaligned_mapping(void* physicalAddress, int flags = MAP_READ_WRITE);
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void* get_unaligned_mappings(void* physicalAddress, uint64_t count, int flags = MAP_READ_WRITE);
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void release_unaligned_mapping(void* mapping);
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void release_unaligned_mappings(void* mapping, uint64_t count);
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void* get_page(int flags = MAP_READ_WRITE);
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void* get_pages(uint64_t count, int flags = MAP_READ_WRITE);
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void* get_page_at(uint64_t addr, int flags = MAP_READ_WRITE);
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void* get_pages_at(uint64_t addr, uint64_t count, int flags = MAP_READ_WRITE);
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void release_page(void* page);
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void release_pages(void* pages, uint64_t count);
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void protect(void* page, uint64_t count, int flags);
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} |