280 lines
12 KiB
C
280 lines
12 KiB
C
/**
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* \file
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* \brief Sector reading and writing implementations
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*/
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#ifndef _FILE_OFFSET_BITS
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#define _FILE_OFFSET_BITS 64
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#endif
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#include <stdlib.h>
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#include <string.h>
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#include "minivhd_internal.h"
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#include "minivhd_util.h"
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/* The following bit array macros adapted from
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http://www.mathcs.emory.edu/~cheung/Courses/255/Syllabus/1-C-intro/bit-array.html */
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#define VHD_SETBIT(A,k) ( A[(k/8)] |= (0x80 >> (k%8)) )
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#define VHD_CLEARBIT(A,k) ( A[(k/8)] &= ~(0x80 >> (k%8)) )
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#define VHD_TESTBIT(A,k) ( A[(k/8)] & (0x80 >> (k%8)) )
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static inline void mvhd_check_sectors(uint32_t offset, int num_sectors, uint32_t total_sectors, int* transfer_sect, int* trunc_sect);
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static void mvhd_read_sect_bitmap(MVHDMeta* vhdm, int blk);
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static void mvhd_write_bat_entry(MVHDMeta* vhdm, int blk);
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static void mvhd_create_block(MVHDMeta* vhdm, int blk);
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static void mvhd_write_curr_sect_bitmap(MVHDMeta* vhdm);
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/**
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* \brief Check that we will not be overflowing buffers
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*
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* \param [in] offset The offset from which we are beginning from
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* \param [in] num_sectors The number of sectors which we desire to read/write
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* \param [in] total_sectors The total number of sectors available
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* \param [out] transfer_sect The number of sectors to actually write.
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* This may be lower than num_sectors if offset + num_sectors >= total_sectors
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* \param [out] trunc_sectors The number of sectors truncated if transfer_sectors < num_sectors
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*/
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static inline void mvhd_check_sectors(uint32_t offset, int num_sectors, uint32_t total_sectors, int* transfer_sect, int* trunc_sect) {
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*transfer_sect = num_sectors;
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*trunc_sect = 0;
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if ((total_sectors - offset) < (uint32_t)*transfer_sect) {
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*transfer_sect = total_sectors - offset;
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*trunc_sect = num_sectors - *transfer_sect;
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}
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}
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void mvhd_write_empty_sectors(FILE* f, int sector_count) {
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uint8_t zero_bytes[MVHD_SECTOR_SIZE] = {0};
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for (int i = 0; i < sector_count; i++) {
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fwrite(zero_bytes, sizeof zero_bytes, 1, f);
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}
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}
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/**
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* \brief Read the sector bitmap for a block.
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*
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* If the block is sparse, the sector bitmap in memory will be
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* zeroed. Otherwise, the sector bitmap is read from the VHD file.
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*
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* \param [in] vhdm MiniVHD data structure
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* \param [in] blk The block for which to read the sector bitmap from
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*/
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static void mvhd_read_sect_bitmap(MVHDMeta* vhdm, int blk) {
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if (vhdm->block_offset[blk] != MVHD_SPARSE_BLK) {
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mvhd_fseeko64(vhdm->f, (uint64_t)vhdm->block_offset[blk] * MVHD_SECTOR_SIZE, SEEK_SET);
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fread(vhdm->bitmap.curr_bitmap, vhdm->bitmap.sector_count * MVHD_SECTOR_SIZE, 1, vhdm->f);
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} else {
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memset(vhdm->bitmap.curr_bitmap, 0, vhdm->bitmap.sector_count * MVHD_SECTOR_SIZE);
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}
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vhdm->bitmap.curr_block = blk;
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}
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/**
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* \brief Write the current sector bitmap in memory to file
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*
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* \param [in] vhdm MiniVHD data structure
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*/
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static void mvhd_write_curr_sect_bitmap(MVHDMeta* vhdm) {
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if (vhdm->bitmap.curr_block >= 0) {
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int64_t abs_offset = (int64_t)vhdm->block_offset[vhdm->bitmap.curr_block] * MVHD_SECTOR_SIZE;
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mvhd_fseeko64(vhdm->f, abs_offset, SEEK_SET);
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fwrite(vhdm->bitmap.curr_bitmap, MVHD_SECTOR_SIZE, vhdm->bitmap.sector_count, vhdm->f);
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}
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}
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/**
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* \brief Write block offset from memory into file
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*
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* \param [in] vhdm MiniVHD data structure
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* \param [in] blk The block for which to write the offset for
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*/
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static void mvhd_write_bat_entry(MVHDMeta* vhdm, int blk) {
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uint64_t table_offset = vhdm->sparse.bat_offset + ((uint64_t)blk * sizeof *vhdm->block_offset);
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uint32_t offset = mvhd_to_be32(vhdm->block_offset[blk]);
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mvhd_fseeko64(vhdm->f, table_offset, SEEK_SET);
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fwrite(&offset, sizeof offset, 1, vhdm->f);
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}
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/**
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* \brief Create an empty block in a sparse or differencing VHD image
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*
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* VHD images store data in blocks, which are typically 4096 sectors in size
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* (~2MB). These blocks may be stored on disk in any order. Blocks are created
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* on demand when required.
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*
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* This function creates new, empty blocks, by replacing the footer at the end of the file
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* and then re-inserting the footer at the new file end. The BAT table entry for the
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* new block is updated with the new offset.
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*
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* \param [in] vhdm MiniVHD data structure
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* \param [in] blk The block number to create
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*/
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static void mvhd_create_block(MVHDMeta* vhdm, int blk) {
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uint8_t footer[MVHD_FOOTER_SIZE];
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/* Seek to where the footer SHOULD be */
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mvhd_fseeko64(vhdm->f, -MVHD_FOOTER_SIZE, SEEK_END);
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fread(footer, sizeof footer, 1, vhdm->f);
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mvhd_fseeko64(vhdm->f, -MVHD_FOOTER_SIZE, SEEK_END);
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if (!mvhd_is_conectix_str(footer)) {
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/* Oh dear. We use the header instead, since something has gone wrong at the footer */
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mvhd_fseeko64(vhdm->f, 0, SEEK_SET);
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fread(footer, sizeof footer, 1, vhdm->f);
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mvhd_fseeko64(vhdm->f, 0, SEEK_END);
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}
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int64_t abs_offset = mvhd_ftello64(vhdm->f);
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if (abs_offset % MVHD_SECTOR_SIZE != 0) {
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/* Yikes! We're supposed to be on a sector boundary. Add some padding */
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int64_t padding_amount = (int64_t)MVHD_SECTOR_SIZE - (abs_offset % MVHD_SECTOR_SIZE);
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uint8_t zero_byte = 0;
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for (int i = 0; i < padding_amount; i++) {
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fwrite(&zero_byte, sizeof zero_byte, 1, vhdm->f);
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}
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abs_offset += padding_amount;
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}
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uint32_t sect_offset = (uint32_t)(abs_offset / MVHD_SECTOR_SIZE);
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int blk_size_sectors = vhdm->sparse.block_sz / MVHD_SECTOR_SIZE;
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mvhd_write_empty_sectors(vhdm->f, vhdm->bitmap.sector_count + blk_size_sectors);
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/* Add a bit of padding. That's what Windows appears to do, although it's not strictly necessary... */
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mvhd_write_empty_sectors(vhdm->f, 5);
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/* And we finish with the footer */
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fwrite(footer, sizeof footer, 1, vhdm->f);
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/* We no longer have a sparse block. Update that BAT! */
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vhdm->block_offset[blk] = sect_offset;
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mvhd_write_bat_entry(vhdm, blk);
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}
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int mvhd_fixed_read(MVHDMeta* vhdm, uint32_t offset, int num_sectors, void* out_buff) {
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int64_t addr;
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int transfer_sectors, truncated_sectors;
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uint32_t total_sectors = (uint32_t)(vhdm->footer.curr_sz / MVHD_SECTOR_SIZE);
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mvhd_check_sectors(offset, num_sectors, total_sectors, &transfer_sectors, &truncated_sectors);
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addr = (int64_t)offset * MVHD_SECTOR_SIZE;
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mvhd_fseeko64(vhdm->f, addr, SEEK_SET);
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fread(out_buff, transfer_sectors*MVHD_SECTOR_SIZE, 1, vhdm->f);
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return truncated_sectors;
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}
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int mvhd_sparse_read(MVHDMeta* vhdm, uint32_t offset, int num_sectors, void* out_buff) {
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int transfer_sectors, truncated_sectors;
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uint32_t total_sectors = (uint32_t)(vhdm->footer.curr_sz / MVHD_SECTOR_SIZE);
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mvhd_check_sectors(offset, num_sectors, total_sectors, &transfer_sectors, &truncated_sectors);
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uint8_t* buff = (uint8_t*)out_buff;
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int64_t addr;
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uint32_t s, ls;
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int blk, prev_blk, sib;
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ls = offset + transfer_sectors;
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prev_blk = -1;
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for (s = offset; s < ls; s++) {
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blk = s / vhdm->sect_per_block;
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sib = s % vhdm->sect_per_block;
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if (blk != prev_blk) {
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prev_blk = blk;
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if (vhdm->bitmap.curr_block != blk) {
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mvhd_read_sect_bitmap(vhdm, blk);
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mvhd_fseeko64(vhdm->f, (uint64_t)sib * MVHD_SECTOR_SIZE, SEEK_CUR);
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} else {
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addr = ((int64_t)vhdm->block_offset[blk] + vhdm->bitmap.sector_count + sib) * MVHD_SECTOR_SIZE;
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mvhd_fseeko64(vhdm->f, addr, SEEK_SET);
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}
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}
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if (VHD_TESTBIT(vhdm->bitmap.curr_bitmap, sib)) {
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fread(buff, MVHD_SECTOR_SIZE, 1, vhdm->f);
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} else {
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memset(buff, 0, MVHD_SECTOR_SIZE);
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mvhd_fseeko64(vhdm->f, MVHD_SECTOR_SIZE, SEEK_CUR);
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}
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buff += MVHD_SECTOR_SIZE;
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}
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return truncated_sectors;
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}
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int mvhd_diff_read(MVHDMeta* vhdm, uint32_t offset, int num_sectors, void* out_buff) {
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int transfer_sectors, truncated_sectors;
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uint32_t total_sectors = (uint32_t)(vhdm->footer.curr_sz / MVHD_SECTOR_SIZE);
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mvhd_check_sectors(offset, num_sectors, total_sectors, &transfer_sectors, &truncated_sectors);
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uint8_t* buff = (uint8_t*)out_buff;
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MVHDMeta* curr_vhdm = vhdm;
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uint32_t s, ls;
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int blk, sib;
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ls = offset + transfer_sectors;
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for (s = offset; s < ls; s++) {
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while (curr_vhdm->footer.disk_type == MVHD_TYPE_DIFF) {
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blk = s / curr_vhdm->sect_per_block;
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sib = s % curr_vhdm->sect_per_block;
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if (curr_vhdm->bitmap.curr_block != blk) {
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mvhd_read_sect_bitmap(curr_vhdm, blk);
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}
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if (!VHD_TESTBIT(curr_vhdm->bitmap.curr_bitmap, sib)) {
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curr_vhdm = curr_vhdm->parent;
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} else { break; }
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}
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/* We handle actual sector reading using the fixed or sparse functions,
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as a differencing VHD is also a sparse VHD */
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if (curr_vhdm->footer.disk_type == MVHD_TYPE_DIFF || curr_vhdm->footer.disk_type == MVHD_TYPE_DYNAMIC) {
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mvhd_sparse_read(curr_vhdm, s, 1, buff);
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} else {
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mvhd_fixed_read(curr_vhdm, s, 1, buff);
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}
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curr_vhdm = vhdm;
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buff += MVHD_SECTOR_SIZE;
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}
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return truncated_sectors;
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}
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int mvhd_fixed_write(MVHDMeta* vhdm, uint32_t offset, int num_sectors, void* in_buff) {
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int64_t addr;
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int transfer_sectors, truncated_sectors;
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uint32_t total_sectors = (uint32_t)(vhdm->footer.curr_sz / MVHD_SECTOR_SIZE);
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mvhd_check_sectors(offset, num_sectors, total_sectors, &transfer_sectors, &truncated_sectors);
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addr = (int64_t)offset * MVHD_SECTOR_SIZE;
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mvhd_fseeko64(vhdm->f, addr, SEEK_SET);
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fwrite(in_buff, transfer_sectors*MVHD_SECTOR_SIZE, 1, vhdm->f);
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return truncated_sectors;
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}
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int mvhd_sparse_diff_write(MVHDMeta* vhdm, uint32_t offset, int num_sectors, void* in_buff) {
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int transfer_sectors, truncated_sectors;
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uint32_t total_sectors = (uint32_t)(vhdm->footer.curr_sz / MVHD_SECTOR_SIZE);
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mvhd_check_sectors(offset, num_sectors, total_sectors, &transfer_sectors, &truncated_sectors);
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uint8_t* buff = (uint8_t*)in_buff;
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int64_t addr;
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uint32_t s, ls;
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int blk, prev_blk, sib;
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ls = offset + transfer_sectors;
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prev_blk = -1;
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for (s = offset; s < ls; s++) {
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blk = s / vhdm->sect_per_block;
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sib = s % vhdm->sect_per_block;
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if (vhdm->bitmap.curr_block != blk && prev_blk >= 0) {
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/* Write the sector bitmap for the previous block, before we replace it. */
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mvhd_write_curr_sect_bitmap(vhdm);
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}
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if (vhdm->block_offset[blk] == MVHD_SPARSE_BLK) {
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/* "read" the sector bitmap first, before creating a new block, as the bitmap will be
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zero either way */
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mvhd_read_sect_bitmap(vhdm, blk);
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mvhd_create_block(vhdm, blk);
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}
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if (blk != prev_blk) {
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if (vhdm->bitmap.curr_block != blk) {
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mvhd_read_sect_bitmap(vhdm, blk);
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mvhd_fseeko64(vhdm->f, (uint64_t)sib * MVHD_SECTOR_SIZE, SEEK_CUR);
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} else {
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addr = ((int64_t)vhdm->block_offset[blk] + vhdm->bitmap.sector_count + sib) * MVHD_SECTOR_SIZE;
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mvhd_fseeko64(vhdm->f, addr, SEEK_SET);
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}
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prev_blk = blk;
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}
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fwrite(buff, MVHD_SECTOR_SIZE, 1, vhdm->f);
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VHD_SETBIT(vhdm->bitmap.curr_bitmap, sib);
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buff += MVHD_SECTOR_SIZE;
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}
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/* And write the sector bitmap for the last block we visited to disk */
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mvhd_write_curr_sect_bitmap(vhdm);
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return truncated_sectors;
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}
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int mvhd_noop_write(MVHDMeta* vhdm, uint32_t offset, int num_sectors, void* in_buff) {
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return 0;
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}
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