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## module functions
**kmem** supplies two module-level functions, used to interact with the `kmptr` container type.
* `kmfree(kmptr) → void` - free, downref, or ignore the pasted object as appropriate
* `kmshred(kmptr) → void` - free, downref, or ignore the pasted object as appropriate. if deallocating, zero its contents
* `kmstat(void*) → kmptr` - convenience function to wrap a pointer to a non-managed object in a `kmptr` struct, so it can be passed to functions that accept arbitrary objects. `kmptr p = kmstat(raw)` is equivalent to `kmptr p = { kmptr_kind_static, raw, NULL }`.
* `kmtaint(&kmptr) → void` - "taints" a `kmptr` object by setting it to be shredded when freed. this may be desirable if the object pointed to contains privileged information.
## types
kmem defines the following types:
* `struct kmptr` - abstract pointer object
* `enum kmptr_kind`
* `struct kmcell` - abstract memory cell
* `enum kmcell_kind`
* `struct kmref` - a reference-counted cell
* `struct kmnode` - a node in an allocation tree
* `struct kmpool` - a memory pool
`kmptr` and `kmcell` are both very similar. the difference is that a kmptr points to a region in memory and can be passed around freely. a `kmcell` is the actual in-memory representation of an allocation cell. a `kmcell` cannot be usefully instantiated; rather, it is downcast from an actual cell type (e.g. `kmnode n; kmcell* s = (kmcell*)(&n)`)
### kmptr
kmem functions can operate on both raw pointers and the `kmptr` struct type. `kmptr` is a generic struct that can contain any kind of pointer. this is useful if you wish to allocate different objects in different manners, but pass them on into a single interface.
memory pointed at by `kmptr` pointers can be freed either with the usual specialized function, or by passing the `kmptr` structure itself to the generic function `kmfree`, which will handle it appropriately, even if it's a pointer to a garbage-collected object or to a static region of memory.
a `kmptr` has the following layout:
* `kmptr_kind kind` - codes the type of pointer
* `kmshred shred` - an enum. if `kmshred_yes`, the value will be zeroed or otherwise made unreadable on free. if no, `kmfree` will consult `src` for shred policy if it is not NULL.
* `void* ref` - the raw pointer enclosed by `cell`
* `kmcell* cell` - a pointer to an object enclosure, typically either a memory pool or a referencing-counting object. NULL if not needed.
the convenience function `kmstat(void*) → kmptr` wraps a pointer to a static object in a `kmptr` struct.
#### kmptr_kind
`kmptr_kind` is an enum with one of the following values.
* `kmptr_kind_none` - not a valid pointer
* `kmptr_kind_static` - points to a static region of space. `kmptr` instances with this kind will be ignored by `kmfree`.
* `kmptr_kind_heap` - a traditional heap pointer.
* `kmptr_kind_pool` - points to a region stored in a memory pool.
* `kmptr_kind_ref` - points to a reference-counted object.
* `kmptr_kind_node` - points to a reference-counted object.
### kmcell
`kmcell` is a stub struct used to disambiguate between source types.a "source" is an object that can hold an allocated object, such as the heap, a memory pool, a fixed-length array on stack, or a fixed-length global array. all values produced by a kmem allocation function point to within a `kmcell`.
* `kmptr_kind kind` - kind of cell
* `size_t sz` - kind of cell (data plus all fields)
* `kmshred shred` - shredding flag
### kmref
`kmref` is a struct that constitutes the in-memory representation of a reference-counted cell.
* `kmcell_kind kind = ref` - kind of cell
* `size_t sz` - size of cell (data plus all fields)
* `kmshred shred` - shredding flag
* `size_t refs` - number of active references
* `kmcell* src` - source, if any
* `char data[]` - content of cell
### kmnode
`kmnode` is a struct that constitutes the in-memory representation of a tree node.
* `kmcell_kind kind = node` - kind of cell
* `size_t sz` - size of cell (data plus all fields)
* `kmshred shred` - shredding flag
* `kmnode* parent` - parent node
* `kmnode* child` - first child node
* `kmnode* lastchild` - last child node
* `kmnode* prev` - previous sibling, NULL if first
* `kmnode* next` - next sibling, NULL if last
* `char data[]` - content of cell
### kmpool
* `kmcell_kind kind = pool` - indicates the kind of source
* `size_t sz` - size of cell (data plus all fields)
* `kmshred shred` - shredding flag
* `size_t cellsz` - size of individual pool cells
* `kmpoolcell* top` - pointer to most recently allocated pool cell
* `kmpoolcell* bottom` - pointer to most recently freed pool cell
* `kmpoolcell data[]` - content of cell
### kmpoolcell
* `kmpoolcell* last` - pointer to last element allocated before this one
* `char data[]` - pool data
### kmshred
`kmshred` is an enum used to indicate whether an object should be "shredded" (written over) in memory when it's deleted. this is a useful means to ensure that privileged information is not accidentally left in memory after use. if the shredding mechanism is not useful, compile libk with the flag `KFmem_noshred` to exclude its functions and fields.
................................................................................
* `tree` [af] - uses a node-child strategy. when a node is freed, all of its children are automatically freed as well.
* `kmtreea(kmcell* src, void* parent, size_t) → void*` - create a tree node. if `parent` is NULL, the node will the top of a new tree. if src is null, allocate on-heap.
* `kmtreez(kmcell* src, void* parent, size_t) → void*` - like `kmtreea` but zeroed
* `kmtreeao(kmcell* src, void* parent, size_t) → kmptr` - like `kmtreea` but returns a `kmptr`
* `kmtreezo(kmcell* src, void* parent, size_t) → kmptr` - like `kmtreez` but returns a `kmptr`
* `kmtreef(void*) → kmptr` - frees a node and all its children
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## module functions
**kmem** supplies two module-level functions, used to interact with the `kmptr` container type.
* `kmfree(kmptr) → void` - free, downref, or ignore the pasted object as appropriate
* `kmshred(kmptr) → void` - free, downref, or ignore the pasted object as appropriate. if deallocating, zero its contents
* `kmstat(void*) → kmptr` - convenience function to wrap a pointer to a non-managed object in a `kmptr` struct, so it can be passed to functions that accept arbitrary objects. `kmptr p = kmstat(raw)` is equivalent to `kmptr p = { kmkind_none, raw, NULL }`.
* `kmtaint(&kmptr) → void` - "taints" a `kmptr` object by setting it to be shredded when freed. this may be desirable if the object pointed to contains privileged information.
## types
kmem defines the following types:
* `enum kmkind` - enumerates allocation strategies
* `struct kmptr` - abstract pointer object
* `struct kmcell` - abstract memory cell
* `struct kmref` - a reference-counted cell
* `struct kmnode` - a node in an allocation tree
* `struct kmpool` - a memory pool
`kmptr` and `kmcell` are both very similar. the difference is that a kmptr points to a region in memory and can be passed around freely. a `kmcell` is the actual in-memory representation of an allocation cell. a `kmcell` cannot be usefully instantiated; rather, it is downcast from an actual cell type (e.g. `kmnode n; kmcell* s = (kmcell*)(&n)`)
### kmkind
`kmkind` is an enum that specifies an allocation function.
* `kmkind_none` - no allocation
* `kmkind_heap` - heap allocation
* `kmkind_pool` - pool allocation
* `kmkind_ref` - reference-counting allocation
* `kmkind_tree` - tree allocation
### kmptr
kmem functions can operate on both raw pointers and the `kmptr` struct type. `kmptr` is a generic struct that can contain any kind of pointer. this is useful if you wish to allocate different objects in different manners, but pass them on into a single interface.
memory pointed at by `kmptr` pointers can be freed either with the usual specialized function, or by passing the `kmptr` structure itself to the generic function `kmfree`, which will handle it appropriately, even if it's a pointer to a garbage-collected object or to a static region of memory.
a `kmptr` has the following layout:
* `kmkind kind` - codes the type of pointer; `kmkind_none` indicates a non-allocated pointer to a static (global or on-stack) object.
* `kmshred shred` - an enum. if `kmshred_yes`, the value will be zeroed or otherwise made unreadable on free. if no, `kmfree` will consult `src` for shred policy if it is not NULL.
* `void* ref` - the raw pointer enclosed by `cell`
* `kmcell* cell` - a pointer to an object enclosure, typically either a memory pool or a referencing-counting object. NULL if not needed.
the convenience function `kmstat(void*) → kmptr` wraps a pointer to a static object in a `kmptr` struct.
### kmcell
`kmcell` is a stub struct used to disambiguate between source types.a "source" is an object that can hold an allocated object, such as the heap, a memory pool, a fixed-length array on stack, or a fixed-length global array. all values produced by a kmem allocation function point to within a `kmcell`.
* `kmptr_kind kind` - kind of cell
* `size_t sz` - kind of cell (data plus all fields)
* `kmshred shred` - shredding flag
### kmref
`kmref` is a struct that constitutes the in-memory representation of a reference-counted cell.
* `kmkind kind = kmkind_ref` - kind of cell
* `size_t sz` - size of cell (data plus all fields)
* `kmshred shred` - shredding flag
* `size_t refs` - number of active references
* `kmcell* src` - source, if any
* `char data[]` - content of cell
### kmnode
`kmnode` is a struct that constitutes the in-memory representation of a tree node.
* `kmkind kind = kmkind_tree` - kind of cell
* `size_t sz` - size of cell (data plus all fields)
* `kmshred shred` - shredding flag
* `kmnode* parent` - parent node
* `kmnode* child` - first child node
* `kmnode* lastchild` - last child node
* `kmnode* prev` - previous sibling, NULL if first
* `kmnode* next` - next sibling, NULL if last
* `char data[]` - content of cell
### kmpool
* `kmkind kind = kmkind_pool` - indicates the kind of source
* `size_t sz` - size of cell (data plus all fields)
* `kmshred shred` - shredding flag
* `size_t cellsz` - size of individual pool cells
* `kmpoolcell* top` - pointer to most recently allocated pool cell
* `kmpoolcell* bottom` - pointer to most recently freed pool cell
* `kmpoolcell data[]` - content of cell
#### kmpoolcell
* `kmpoolcell* last` - pointer to last element allocated before this one
* `char data[]` - pool data
### kmshred
`kmshred` is an enum used to indicate whether an object should be "shredded" (written over) in memory when it's deleted. this is a useful means to ensure that privileged information is not accidentally left in memory after use. if the shredding mechanism is not useful, compile libk with the flag `KFmem_noshred` to exclude its functions and fields.
................................................................................
* `tree` [af] - uses a node-child strategy. when a node is freed, all of its children are automatically freed as well.
* `kmtreea(kmcell* src, void* parent, size_t) → void*` - create a tree node. if `parent` is NULL, the node will the top of a new tree. if src is null, allocate on-heap.
* `kmtreez(kmcell* src, void* parent, size_t) → void*` - like `kmtreea` but zeroed
* `kmtreeao(kmcell* src, void* parent, size_t) → kmptr` - like `kmtreea` but returns a `kmptr`
* `kmtreezo(kmcell* src, void* parent, size_t) → kmptr` - like `kmtreez` but returns a `kmptr`
* `kmtreef(void*) → kmptr` - frees a node and all its children
## macros
kmem defines the following macros.
* `Kmsz(array)` - a convenience macro to return the number of elements in a static array. inserts the text `( sizeof (array) / sizeof (array) [0] )`
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