// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <minfs/transaction-limits.h>

namespace minfs {

blk_t GetBlockBitmapBlocks(const Superblock& info) {
    ZX_DEBUG_ASSERT(info.ino_block >= info.abm_block);
    blk_t bitmap_blocks = info.ino_block - info.abm_block;

    if (info.flags & kMinfsFlagFVM) {
        const blk_t kBlocksPerSlice = static_cast<blk_t>(info.slice_size / kMinfsBlockSize);
        bitmap_blocks = info.abm_slices * kBlocksPerSlice;
    }

    return bitmap_blocks;
}

zx_status_t GetRequiredBlockCount(size_t offset, size_t length, blk_t* num_req_blocks) {
    if (length == 0) {
        // Return early if no data needs to be written.
        *num_req_blocks = 0;
        return ZX_OK;
    }

    // Determine which range of direct blocks will be accessed given offset and length,
    // and add to total.
    blk_t first_direct = static_cast<blk_t>(offset / kMinfsBlockSize);
    blk_t last_direct = static_cast<blk_t>((offset + length - 1) / kMinfsBlockSize);
    blk_t reserve_blocks = last_direct - first_direct + 1;

    if (last_direct >= kMinfsDirect) {
        // If direct blocks go into indirect range, adjust the indices accordingly.
        first_direct = fbl::max(first_direct, kMinfsDirect) - kMinfsDirect;
        last_direct -= kMinfsDirect;

        // Calculate indirect blocks containing first and last direct blocks, and add to total.
        blk_t first_indirect = first_direct / kMinfsDirectPerIndirect;
        blk_t last_indirect = last_direct / kMinfsDirectPerIndirect;
        reserve_blocks += last_indirect - first_indirect + 1;

        if (last_indirect >= kMinfsIndirect) {
            // If indirect blocks go into doubly indirect range, adjust the indices accordingly.
            first_indirect = fbl::max(first_indirect, kMinfsIndirect) - kMinfsIndirect;
            last_indirect -= kMinfsIndirect;

            // Calculate doubly indirect blocks containing first/last indirect blocks,
            // and add to total
            blk_t first_dindirect = first_indirect / kMinfsDirectPerIndirect;
            blk_t last_dindirect = last_indirect / kMinfsDirectPerIndirect;
            reserve_blocks += last_dindirect - first_dindirect + 1;

            if (last_dindirect >= kMinfsDoublyIndirect) {
                // We cannot allocate blocks which exceed the doubly indirect range.
                return ZX_ERR_OUT_OF_RANGE;
            }
        }
    }

    *num_req_blocks = reserve_blocks;
    return ZX_OK;
}

TransactionLimits::TransactionLimits(const Superblock& info) {
    CalculateDataBlocks();
    CalculateJournalBlocks(GetBlockBitmapBlocks(info));
}

void TransactionLimits::CalculateDataBlocks() {
    // If we ever increase the number of doubly indirect blocks, we will need to update this offset
    // to be 1 byte before the end of the first doubly indirect block.
    constexpr blk_t kOffset =
        (kMinfsDirect + (kMinfsIndirect * kMinfsDirectPerIndirect)) * kMinfsBlockSize - 1;

    // This calculation ignores the fact that directory size is capped at |kMinfsMaxDirectorySize|,
    // because following that constraint makes it a little harder to predict where the most
    // significant cross-block write would be. This means we may overestimate the maximum number of
    // directory blocks by some amount, but this is better than an understimate.
    blk_t max_directory_blocks;
    ZX_ASSERT(GetRequiredBlockCount(kOffset, kMinfsMaxDirentSize, &max_directory_blocks) == ZX_OK);
    ZX_ASSERT(GetRequiredBlockCount(kOffset, kMaxWriteBytes, &max_data_blocks_) == ZX_OK);

    blk_t direct_blocks = (fbl::round_up(kMaxWriteBytes, kMinfsBlockSize) / kMinfsBlockSize) + 1;
    blk_t max_indirect_blocks = max_data_blocks_ - direct_blocks;

    max_meta_data_blocks_ = fbl::max(max_directory_blocks, max_indirect_blocks);
}

void TransactionLimits::CalculateJournalBlocks(blk_t block_bitmap_blocks) {
    max_entry_data_blocks_ = kMaxSuperblockBlocks + kMaxInodeBitmapBlocks + block_bitmap_blocks
                             + kMaxInodeTableBlocks + max_meta_data_blocks_;

    // Ensure we have enough space to fit all the block numbers that may be updated in one
    // transaction. This may spill over into multiple blocks.
    blk_t header_blocks = 1;
    if (max_entry_data_blocks_ > kJournalEntryHeaderMaxBlocks) {
        header_blocks += fbl::round_up((max_entry_data_blocks_ - kJournalEntryHeaderMaxBlocks),
                                       kMinfsDirectPerIndirect) / kMinfsDirectPerIndirect;
    }

    // For revocation records, we need to know the maximum number of metadata blocks within the
    // data section of Minfs that can be deleted within one operation. This is either a directory
    // vnode's maximum possible number of data blocks + indirect blocks, or a data vnode's maximum
    // possible number of indirect blocks.
    blk_t maximum_directory_blocks;
    ZX_ASSERT(GetRequiredBlockCount(0, kMinfsMaxDirectorySize, &maximum_directory_blocks) == ZX_OK);
    blk_t maximum_indirect_blocks = kMinfsIndirect + kMinfsDoublyIndirect * kMinfsDirectPerIndirect;
    blk_t revocation_blocks = fbl::round_up(fbl::max(maximum_directory_blocks,
                                                     maximum_indirect_blocks),
                                            kMinfsDirectPerIndirect)
                              / kMinfsDirectPerIndirect;

    blk_t commit_blocks = 1;

    max_entry_blocks_ = header_blocks + revocation_blocks + max_entry_data_blocks_ + commit_blocks;
    min_journal_blocks_ = max_entry_blocks_ + kJournalMetadataBlocks;
    rec_journal_blocks_ = fbl::max(min_journal_blocks_, kDefaultJournalBlocks);
}

} // namespace minfs