/*
* \brief Data structure for storing sparse files in RAM
* \author Norman Feske
* \date 2012-04-18
*/
/*
* Copyright (C) 2012-2017 Genode Labs GmbH
*
* This file is part of the Genode OS framework, which is distributed
* under the terms of the GNU Affero General Public License version 3.
*/
#ifndef _INCLUDE__RAM_FS__CHUNK_H_
#define _INCLUDE__RAM_FS__CHUNK_H_
/* Genode includes */
#include <util/noncopyable.h>
#include <base/allocator.h>
#include <util/string.h>
#include <file_system_session/file_system_session.h>
namespace File_system {
using namespace Genode;
using Genode::Noncopyable;
class Chunk_base;
template <unsigned> class Chunk;
template <unsigned, typename> class Chunk_index;
}
/**
* Common base class of both 'Chunk' and 'Chunk_index'
*/
class File_system::Chunk_base : Noncopyable
{
public:
class Index_out_of_range { };
protected:
seek_off_t const _base_offset;
size_t _num_entries; /* corresponds to last used entry */
/**
* Test if specified range lies within the chunk
*/
void assert_valid_range(seek_off_t start, size_t len,
file_size_t chunk_size) const
{
if (zero()) return;
if (start < _base_offset)
throw Index_out_of_range();
if (start + len > _base_offset + chunk_size)
throw Index_out_of_range();
}
Chunk_base(seek_off_t base_offset)
: _base_offset(base_offset), _num_entries(0) { }
/**
* Construct zero chunk
*
* A zero chunk is a chunk that cannot be written to. When reading
* from it, it returns zeros. Because there is a single zero chunk
* for each chunk type, the base offset is meaningless. We use a
* base offset of ~0 as marker to identify zero chunks.
*/
Chunk_base() : _base_offset(~0L), _num_entries(0) { }
public:
/**
* Return absolute base offset of chunk in bytes
*/
seek_off_t base_offset() const { return _base_offset; }
/**
* Return true if chunk is a read-only zero chunk
*/
bool zero() const { return _base_offset == (seek_off_t)(~0L); }
/**
* Return true if chunk has no allocated sub chunks
*/
bool empty() const { return _num_entries == 0; }
};
/**
* Chunk of bytes used as leaf in hierarchy of chunk indices
*/
template <unsigned CHUNK_SIZE>
class File_system::Chunk : public Chunk_base
{
private:
char _data[CHUNK_SIZE];
public:
enum { SIZE = CHUNK_SIZE };
/**
* Construct byte chunk
*
* \param base_offset absolute offset of chunk in bytes
*
* The first argument is unused. Its mere purpose is to make the
* signature of the constructor compatible to the constructor
* of 'Chunk_index'.
*/
Chunk(Allocator &, seek_off_t base_offset)
:
Chunk_base(base_offset)
{
memset(_data, 0, CHUNK_SIZE);
}
/**
* Construct zero chunk
*/
Chunk() { }
/**
* Return number of used entries
*
* The returned value corresponds to the index of the last used
* entry + 1. It does not correlate to the number of actually
* allocated entries (there may be ranges of zero blocks).
*/
file_size_t used_size() const { return _num_entries; }
void write(char const *src, size_t len, seek_off_t seek_offset)
{
assert_valid_range(seek_offset, len, SIZE);
/* offset relative to this chunk */
seek_off_t const local_offset = seek_offset - base_offset();
memcpy(&_data[local_offset], src, len);
_num_entries = max(_num_entries, local_offset + len);
}
void read(char *dst, size_t len, seek_off_t seek_offset) const
{
assert_valid_range(seek_offset, len, SIZE);
memcpy(dst, &_data[seek_offset - base_offset()], len);
}
void truncate(file_size_t size)
{
assert_valid_range(size, 0, SIZE);
/*
* Offset of the first free position (relative to the beginning
* this chunk).
*/
seek_off_t const local_offset = size - base_offset();
if (local_offset >= _num_entries)
return;
memset(&_data[local_offset], 0, _num_entries - local_offset);
_num_entries = local_offset;
}
};
template <unsigned NUM_ENTRIES, typename ENTRY_TYPE>
class File_system::Chunk_index : public Chunk_base
{
public:
typedef ENTRY_TYPE Entry;
enum { ENTRY_SIZE = ENTRY_TYPE::SIZE,
SIZE = ENTRY_SIZE*NUM_ENTRIES };
private:
/*
* Noncopyable
*/
Chunk_index(Chunk_index const &);
Chunk_index &operator = (Chunk_index const &);
Allocator &_alloc;
Entry * _entries[NUM_ENTRIES];
/**
* Return instance of a zero sub chunk
*/
static Entry const &_zero_chunk()
{
static Entry zero_chunk;
return zero_chunk;
}
/**
* Return sub chunk at given index
*
* If there is no sub chunk at the specified index, this function
* transparently allocates one. Hence, the returned sub chunk
* is ready to be written to.
*/
Entry &_entry_for_writing(unsigned index)
{
if (index >= NUM_ENTRIES)
throw Index_out_of_range();
if (_entries[index])
return *_entries[index];
seek_off_t entry_offset = base_offset() + index*ENTRY_SIZE;
_entries[index] = new (&_alloc) Entry(_alloc, entry_offset);
_num_entries = max(_num_entries, index + 1);
return *_entries[index];
}
/**
* Return sub chunk at given index (for reading only)
*
* This function transparently provides a zero sub chunk for any
* index that is not populated by a real chunk.
*/
Entry const &_entry_for_reading(unsigned index) const
{
if (index >= NUM_ENTRIES)
throw Index_out_of_range();
if (_entries[index])
return *_entries[index];
return _zero_chunk();
}
/**
* Return index of entry located at specified byte offset
*
* The caller of this function must make sure that the offset
* parameter is within the bounds of the chunk.
*/
unsigned _index_by_offset(seek_off_t offset) const
{
return (offset - base_offset()) / ENTRY_SIZE;
}
/**
* Apply operation 'func' to a range of entries
*/
template <typename THIS, typename DATA, typename FUNC>
static void _range_op(THIS &obj, DATA *data, size_t len,
seek_off_t seek_offset, FUNC const &func)
{
/*
* Depending on whether this function is called for reading
* (const function) or writing (non-const function), the
* operand type is const or non-const Entry. The correct type
* is embedded as a trait in the 'FUNC' functor type.
*/
typedef typename FUNC::Entry Const_qualified_entry;
obj.assert_valid_range(seek_offset, len, SIZE);
while (len > 0) {
unsigned const index = obj._index_by_offset(seek_offset);
Const_qualified_entry &entry = FUNC::lookup(obj, index);
/*
* Calculate byte offset relative to the chunk
*
* We cannot use 'entry.base_offset()' for this calculation
* because in the const case, the lookup might return a
* zero chunk, which has no defined base offset. Therefore,
* we calculate the base offset via index*ENTRY_SIZE.
*/
seek_off_t const local_seek_offset =
seek_offset - obj.base_offset() - index*ENTRY_SIZE;
/* available capacity at 'entry' starting at seek offset */
seek_off_t const capacity = ENTRY_SIZE - local_seek_offset;
seek_off_t const curr_len = min(len, capacity);
/* apply functor (read or write) to entry */
func(entry, data, curr_len, seek_offset);
/* advance to next entry */
len -= curr_len;
data += curr_len;
seek_offset += curr_len;
}
}
struct Write_func
{
typedef ENTRY_TYPE Entry;
static Entry &lookup(Chunk_index &chunk, unsigned i) {
return chunk._entry_for_writing(i); }
void operator () (Entry &entry, char const *src, size_t len,
seek_off_t seek_offset) const
{
entry.write(src, len, seek_offset);
}
};
struct Read_func
{
typedef ENTRY_TYPE const Entry;
static Entry &lookup(Chunk_index const &chunk, unsigned i) {
return chunk._entry_for_reading(i); }
void operator () (Entry &entry, char *dst, size_t len,
seek_off_t seek_offset) const
{
if (entry.zero())
memset(dst, 0, len);
else
entry.read(dst, len, seek_offset);
}
};
void _init_entries()
{
for (unsigned i = 0; i < NUM_ENTRIES; i++)
_entries[i] = 0;
}
void _destroy_entry(unsigned i)
{
if (_entries[i] && (i < _num_entries)) {
destroy(&_alloc, _entries[i]);
_entries[i] = 0;
}
}
public:
/**
* Constructor
*
* \param alloc allocator to use for allocating sub-chunk
* indices and chunks
* \param base_offset absolute offset of the chunk in bytes
*/
Chunk_index(Allocator &alloc, seek_off_t base_offset)
: Chunk_base(base_offset), _alloc(alloc) { _init_entries(); }
/**
* Construct zero chunk
*/
Chunk_index() : _alloc(*(Allocator *)0) { }
/**
* Destructor
*/
~Chunk_index()
{
for (unsigned i = 0; i < NUM_ENTRIES; i++)
_destroy_entry(i);
}
/**
* Return size of chunk in bytes
*
* The returned value corresponds to the position after the highest
* offset that was written to.
*/
file_size_t used_size() const
{
if (_num_entries == 0)
return 0;
/* size of entries that lie completely within the used range */
file_size_t const size_whole_entries = ENTRY_SIZE*(_num_entries - 1);
Entry *last_entry = _entries[_num_entries - 1];
if (!last_entry)
return size_whole_entries;
return size_whole_entries + last_entry->used_size();
}
/**
* Write data to chunk
*/
void write(char const *src, size_t len, seek_off_t seek_offset)
{
_range_op(*this, src, len, seek_offset, Write_func());
}
/**
* Read data from chunk
*/
void read(char *dst, size_t len, seek_off_t seek_offset) const
{
_range_op(*this, dst, len, seek_offset, Read_func());
}
/**
* Truncate chunk to specified size in bytes
*
* This function can be used to shrink a chunk only. Specifying a
* 'size' larger than 'used_size' has no effect. The value returned
* by 'used_size' refers always to the position of the last byte
* written to the chunk.
*/
void truncate(file_size_t size)
{
unsigned const trunc_index = _index_by_offset(size);
if (trunc_index >= _num_entries)
return;
for (unsigned i = trunc_index + 1; i < _num_entries; i++)
_destroy_entry(i);
/* traverse into sub chunks */
if (_entries[trunc_index])
_entries[trunc_index]->truncate(size);
_num_entries = trunc_index + 1;
/*
* If the truncated at a chunk boundary, we can release the
* empty trailing chunk at 'trunc_index'.
*/
if (_entries[trunc_index] && _entries[trunc_index]->empty()) {
_destroy_entry(trunc_index);
_num_entries--;
}
}
};
#endif /* _INCLUDE__RAM_FS__CHUNK_H_ */