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78 lines
2.5 KiB
78 lines
2.5 KiB
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 |
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From: Daniel Axtens <dja@axtens.net> |
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Date: Thu, 25 Nov 2021 02:22:45 +1100 |
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Subject: [PATCH] mm: Document GRUB internal memory management structures |
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I spent more than a trivial quantity of time figuring out pre_size and |
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whether a memory region's size contains the header cell or not. |
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Document the meanings of all the properties. Hopefully now no-one else |
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has to figure it out! |
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Signed-off-by: Daniel Axtens <dja@axtens.net> |
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com> |
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(cherry picked from commit a6c5c52ccffd2674d43db25fb4baa9c528526aa0) |
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--- |
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include/grub/mm_private.h | 28 ++++++++++++++++++++++++++++ |
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1 file changed, 28 insertions(+) |
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diff --git a/include/grub/mm_private.h b/include/grub/mm_private.h |
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index c2c4cb1511..203533cc3d 100644 |
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--- a/include/grub/mm_private.h |
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+++ b/include/grub/mm_private.h |
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@@ -21,15 +21,27 @@ |
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#include <grub/mm.h> |
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+/* For context, see kern/mm.c */ |
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+ |
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/* Magic words. */ |
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#define GRUB_MM_FREE_MAGIC 0x2d3c2808 |
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#define GRUB_MM_ALLOC_MAGIC 0x6db08fa4 |
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+/* A header describing a block of memory - either allocated or free */ |
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typedef struct grub_mm_header |
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{ |
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+ /* |
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+ * The 'next' free block in this region's circular free list. |
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+ * Only meaningful if the block is free. |
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+ */ |
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struct grub_mm_header *next; |
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+ /* The block size, not in bytes but the number of cells of |
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+ * GRUB_MM_ALIGN bytes. Includes the header cell. |
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+ */ |
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grub_size_t size; |
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+ /* either free or alloc magic, depending on the block type. */ |
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grub_size_t magic; |
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+ /* pad to cell size: see the top of kern/mm.c. */ |
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#if GRUB_CPU_SIZEOF_VOID_P == 4 |
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char padding[4]; |
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#elif GRUB_CPU_SIZEOF_VOID_P == 8 |
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@@ -48,11 +60,27 @@ typedef struct grub_mm_header |
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#define GRUB_MM_ALIGN (1 << GRUB_MM_ALIGN_LOG2) |
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+/* A region from which we can make allocations. */ |
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typedef struct grub_mm_region |
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{ |
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+ /* The first free block in this region. */ |
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struct grub_mm_header *first; |
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+ |
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+ /* |
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+ * The next region in the linked list of regions. Regions are initially |
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+ * sorted in order of increasing size, but can grow, in which case the |
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+ * ordering may not be preserved. |
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+ */ |
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struct grub_mm_region *next; |
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+ |
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+ /* |
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+ * A grub_mm_region will always be aligned to cell size. The pre-size is |
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+ * the number of bytes we were given but had to skip in order to get that |
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+ * alignment. |
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+ */ |
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grub_size_t pre_size; |
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+ |
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+ /* How many bytes are in this region? (free and allocated) */ |
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grub_size_t size; |
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} |
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*grub_mm_region_t;
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