backed_block.cpp

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <assert.h>
#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

#include "backed_block.h"
#include "sparse_defs.h"

struct backed_block {
  unsigned int block;
  unsigned int len;
  enum backed_block_type type;
  union {
    struct {
      void* data;
    } data;
    struct {
      char* filename;
      int64_t offset;
    } file;
    struct {
      int fd;
      int64_t offset;
    } fd;
    struct {
      uint32_t val;
    } fill;
  };
  struct backed_block* next;
};

struct backed_block_list {
  struct backed_block* data_blocks;
  struct backed_block* last_used;
  unsigned int block_size;
};

struct backed_block* backed_block_iter_new(struct backed_block_list* bbl) {
  return bbl->data_blocks;
}

struct backed_block* backed_block_iter_next(struct backed_block* bb) {
  return bb->next;
}

unsigned int backed_block_len(struct backed_block* bb) {
  return bb->len;
}

unsigned int backed_block_block(struct backed_block* bb) {
  return bb->block;
}

void* backed_block_data(struct backed_block* bb) {
  assert(bb->type == BACKED_BLOCK_DATA);
  return bb->data.data;
}

const char* backed_block_filename(struct backed_block* bb) {
  assert(bb->type == BACKED_BLOCK_FILE);
  return bb->file.filename;
}

int backed_block_fd(struct backed_block* bb) {
  assert(bb->type == BACKED_BLOCK_FD);
  return bb->fd.fd;
}

int64_t backed_block_file_offset(struct backed_block* bb) {
  assert(bb->type == BACKED_BLOCK_FILE || bb->type == BACKED_BLOCK_FD);
  if (bb->type == BACKED_BLOCK_FILE) {
    return bb->file.offset;
  } else { /* bb->type == BACKED_BLOCK_FD */
    return bb->fd.offset;
  }
}

uint32_t backed_block_fill_val(struct backed_block* bb) {
  assert(bb->type == BACKED_BLOCK_FILL);
  return bb->fill.val;
}

enum backed_block_type backed_block_type(struct backed_block* bb) {
  return bb->type;
}

void backed_block_destroy(struct backed_block* bb) {
  if (bb->type == BACKED_BLOCK_FILE) {
    free(bb->file.filename);
  }

  free(bb);
}

struct backed_block_list* backed_block_list_new(unsigned int block_size) {
  struct backed_block_list* b =
      reinterpret_cast<backed_block_list*>(calloc(1, sizeof(struct backed_block_list)));
  b->block_size = block_size;
  return b;
}

void backed_block_list_destroy(struct backed_block_list* bbl) {
  if (bbl->data_blocks) {
    struct backed_block* bb = bbl->data_blocks;
    while (bb) {
      struct backed_block* next = bb->next;
      backed_block_destroy(bb);
      bb = next;
    }
  }

  free(bbl);
}

void backed_block_list_move(struct backed_block_list* from, struct backed_block_list* to,
                            struct backed_block* start, struct backed_block* end) {
  struct backed_block* bb;

  if (start == nullptr) {
    start = from->data_blocks;
  }

  if (!end) {
    for (end = start; end && end->next; end = end->next)
      ;
  }

  if (start == nullptr || end == nullptr) {
    return;
  }

  from->last_used = nullptr;
  to->last_used = nullptr;
  if (from->data_blocks == start) {
    from->data_blocks = end->next;
  } else {
    for (bb = from->data_blocks; bb; bb = bb->next) {
      if (bb->next == start) {
        bb->next = end->next;
        break;
      }
    }
  }

  if (!to->data_blocks) {
    to->data_blocks = start;
    end->next = nullptr;
  } else {
    for (bb = to->data_blocks; bb; bb = bb->next) {
      if (!bb->next || bb->next->block > start->block) {
        end->next = bb->next;
        bb->next = start;
        break;
      }
    }
  }
}

/* may free b */
static int merge_bb(struct backed_block_list* bbl, struct backed_block* a, struct backed_block* b) {
  unsigned int block_len;

  /* Block doesn't exist (possible if one block is the last block) */
  if (!a || !b) {
    return -EINVAL;
  }

  assert(a->block < b->block);

  /* Blocks are of different types */
  if (a->type != b->type) {
    return -EINVAL;
  }

  /* Blocks are not adjacent */
  block_len = a->len / bbl->block_size; /* rounds down */
  if (a->block + block_len != b->block) {
    return -EINVAL;
  }

  switch (a->type) {
    case BACKED_BLOCK_DATA:
      /* Don't support merging data for now */
      return -EINVAL;
    case BACKED_BLOCK_FILL:
      if (a->fill.val != b->fill.val) {
        return -EINVAL;
      }
      break;
    case BACKED_BLOCK_FILE:
      /* Already make sure b->type is BACKED_BLOCK_FILE */
      if (strcmp(a->file.filename, b->file.filename) || a->file.offset + a->len != b->file.offset) {
        return -EINVAL;
      }
      break;
    case BACKED_BLOCK_FD:
      if (a->fd.fd != b->fd.fd || a->fd.offset + a->len != b->fd.offset) {
        return -EINVAL;
      }
      break;
  }

  /* Blocks are compatible and adjacent, with a before b.  Merge b into a,
   * and free b */
  a->len += b->len;
  a->next = b->next;

  backed_block_destroy(b);

  return 0;
}

static int queue_bb(struct backed_block_list* bbl, struct backed_block* new_bb) {
  struct backed_block* bb;

  if (bbl->data_blocks == nullptr) {
    bbl->data_blocks = new_bb;
    return 0;
  }

  if (bbl->data_blocks->block > new_bb->block) {
    new_bb->next = bbl->data_blocks;
    bbl->data_blocks = new_bb;
    return 0;
  }

  /* Optimization: blocks are mostly queued in sequence, so save the
     pointer to the last bb that was added, and start searching from
     there if the next block number is higher */
  if (bbl->last_used && new_bb->block > bbl->last_used->block)
    bb = bbl->last_used;
  else
    bb = bbl->data_blocks;
  bbl->last_used = new_bb;

  for (; bb->next && bb->next->block < new_bb->block; bb = bb->next)
    ;

  if (bb->next == nullptr) {
    bb->next = new_bb;
  } else {
    new_bb->next = bb->next;
    bb->next = new_bb;
  }

  merge_bb(bbl, new_bb, new_bb->next);
  if (!merge_bb(bbl, bb, new_bb)) {
    /* new_bb destroyed, point to retained as last_used */
    bbl->last_used = bb;
  }

  return 0;
}

/* Queues a fill block of memory to be written to the specified data blocks */
int backed_block_add_fill(struct backed_block_list* bbl, unsigned int fill_val, unsigned int len,
                          unsigned int block) {
  struct backed_block* bb = reinterpret_cast<backed_block*>(calloc(1, sizeof(struct backed_block)));
  if (bb == nullptr) {
    return -ENOMEM;
  }

  bb->block = block;
  bb->len = len;
  bb->type = BACKED_BLOCK_FILL;
  bb->fill.val = fill_val;
  bb->next = nullptr;

  return queue_bb(bbl, bb);
}

/* Queues a block of memory to be written to the specified data blocks */
int backed_block_add_data(struct backed_block_list* bbl, void* data, unsigned int len,
                          unsigned int block) {
  struct backed_block* bb = reinterpret_cast<backed_block*>(calloc(1, sizeof(struct backed_block)));
  if (bb == nullptr) {
    return -ENOMEM;
  }

  bb->block = block;
  bb->len = len;
  bb->type = BACKED_BLOCK_DATA;
  bb->data.data = data;
  bb->next = nullptr;

  return queue_bb(bbl, bb);
}

/* Queues a chunk of a file on disk to be written to the specified data blocks */
int backed_block_add_file(struct backed_block_list* bbl, const char* filename, int64_t offset,
                          unsigned int len, unsigned int block) {
  struct backed_block* bb = reinterpret_cast<backed_block*>(calloc(1, sizeof(struct backed_block)));
  if (bb == nullptr) {
    return -ENOMEM;
  }

  bb->block = block;
  bb->len = len;
  bb->type = BACKED_BLOCK_FILE;
  bb->file.filename = strdup(filename);
  bb->file.offset = offset;
  bb->next = nullptr;

  return queue_bb(bbl, bb);
}

/* Queues a chunk of a fd to be written to the specified data blocks */
int backed_block_add_fd(struct backed_block_list* bbl, int fd, int64_t offset, unsigned int len,
                        unsigned int block) {
  struct backed_block* bb = reinterpret_cast<backed_block*>(calloc(1, sizeof(struct backed_block)));
  if (bb == nullptr) {
    return -ENOMEM;
  }

  bb->block = block;
  bb->len = len;
  bb->type = BACKED_BLOCK_FD;
  bb->fd.fd = fd;
  bb->fd.offset = offset;
  bb->next = nullptr;

  return queue_bb(bbl, bb);
}

int backed_block_split(struct backed_block_list* bbl, struct backed_block* bb,
                       unsigned int max_len) {
  struct backed_block* new_bb;

  max_len = ALIGN_DOWN(max_len, bbl->block_size);

  if (bb->len <= max_len) {
    return 0;
  }

  new_bb = reinterpret_cast<backed_block*>(malloc(sizeof(struct backed_block)));
  if (new_bb == nullptr) {
    return -ENOMEM;
  }

  *new_bb = *bb;

  new_bb->len = bb->len - max_len;
  new_bb->block = bb->block + max_len / bbl->block_size;
  new_bb->next = bb->next;
  bb->next = new_bb;
  bb->len = max_len;

  switch (bb->type) {
    case BACKED_BLOCK_DATA:
      new_bb->data.data = (char*)bb->data.data + max_len;
      break;
    case BACKED_BLOCK_FILE:
      new_bb->file.offset += max_len;
      break;
    case BACKED_BLOCK_FD:
      new_bb->fd.offset += max_len;
      break;
    case BACKED_BLOCK_FILL:
      break;
  }

  return 0;
}