I spent more than a trivial quantity of time figuring out pre_size and
whether a memory region's size contains the header cell or not.
Document the meanings of all the properties. Hopefully now no-one else
has to figure it out!
Signed-off-by: Daniel Axtens <d...@axtens.net>
---
include/grub/mm_private.h | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/include/grub/mm_private.h b/include/grub/mm_private.h
index c2c4cb1511c6..e80a059dd4e4 100644
--- a/include/grub/mm_private.h
+++ b/include/grub/mm_private.h
@@ -25,11 +25,18 @@
#define GRUB_MM_FREE_MAGIC 0x2d3c2808
#define GRUB_MM_ALLOC_MAGIC 0x6db08fa4
+/* A header describing a block of memory - either allocated or free */
typedef struct grub_mm_header
{
+ /* The 'next' free block in this region. A circular list.
+ Only meaningful if the block is free.
+ */
struct grub_mm_header *next;
+ /* The region size in cells (not bytes). Includes the header cell. */
grub_size_t size;
+ /* either free or alloc magic, depending on the block type. */
grub_size_t magic;
+ /* pad to cell size: see the top of mm.c. */
#if GRUB_CPU_SIZEOF_VOID_P == 4
char padding[4];
#elif GRUB_CPU_SIZEOF_VOID_P == 8
@@ -48,11 +55,25 @@ typedef struct grub_mm_header
#define GRUB_MM_ALIGN (1 << GRUB_MM_ALIGN_LOG2)
+/* A region from which we can make allocations. */
typedef struct grub_mm_region
{
+ /* The first free block in this region. */
struct grub_mm_header *first;
+
+ /* The next region in the linked list of regions. Regions are initially
+ sorted in order of increasing size, but can grow, in which case the
+ ordering may not be preserved.
+ */
struct grub_mm_region *next;
+
+ /* A grub_mm_region will always be aligned to cell size. The pre-size is
+ the number of bytes we were given but had to skip in order to get that
+ alignment.
+ */
grub_size_t pre_size;
+
+ /* How many bytes are in this region? (free and allocated) */
grub_size_t size;
}
*grub_mm_region_t;
--
2.30.2
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