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feat(mkdwarfs): improve performance and safety when rewriting image

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This commit is contained in:
Marcus Holland-Moritz 2023-12-17 12:24:43 +01:00
parent de3ee6cc42
commit 1db93c813b
1 changed files with 25 additions and 3 deletions
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28
src/dwarfs/filesystem_writer.cpp
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@ -127,7 +127,8 @@ class fsblock {
};
static void
build_section_header(section_header_v2& sh, fsblock::impl const& fsb);
build_section_header(section_header_v2& sh, fsblock::impl const& fsb,
std::optional<fs_section> const& sec = std::nullopt);
private:
std::unique_ptr<impl> impl_;
@ -276,7 +277,7 @@ class compressed_fsblock : public fsblock::impl {
future_ = prom.get_future();
wg.add_job([this, prom = std::move(prom)]() mutable {
fsblock::build_section_header(header_, *this);
fsblock::build_section_header(header_, *this, sec_);
if (pctx_) {
pctx_->bytes_in += size();
pctx_->bytes_out += size();
@ -444,7 +445,8 @@ fsblock::fsblock(section_type type, block_compressor const& bc,
std::move(pctx))) {}
void fsblock::build_section_header(section_header_v2& sh,
fsblock::impl const& fsb) {
fsblock::impl const& fsb,
std::optional<fs_section> const& sec) {
auto range = fsb.data();
::memcpy(&sh.magic[0], "DWARFS", 6);
@ -455,6 +457,26 @@ void fsblock::build_section_header(section_header_v2& sh,
sh.compression = static_cast<uint16_t>(fsb.compression());
sh.length = range.size();
if (sec) {
// This isn't just an optimization, it is actually a bit of a safety
// feature. If we have an existing section header that we've previously
// validated and we use its checksums, we can be sure that any mistake
// in copying the data will be detected.
auto secnum = sec->section_number();
if (secnum && secnum.value() == sh.number) {
auto xxh = sec->xxh3_64_value();
auto sha = sec->sha2_512_256_value();
if (xxh && sha && sha->size() == sizeof(sh.sha2_512_256)) {
sh.xxh3_64 = xxh.value();
std::copy(sha->begin(), sha->end(), &sh.sha2_512_256[0]);
return;
}
}
}
checksum xxh(checksum::algorithm::XXH3_64);
xxh.update(&sh.number,
sizeof(section_header_v2) - offsetof(section_header_v2, number));