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c124f6ba5209cb088a40e13c38f8f6b4e536e608
psxrecomp/runtime/src/mod_resident.cpp
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Matthew Stanley ddd903014f Keep resident packs in memory when the cache is unwritable and record adapter requests in an always-on ring 
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
2026-10-05 22:52:52 -07:00

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/* Resident disc resources for seamless-loading adapters (mod_resident.h).
*
* Pack file (little endian):
* "PSXRES01", u32 version, u32 files, u32 derived, u32 blobs,
* u8 key[32], u64 payload_bytes,
* files[] {u32 lba, size, padded, stock, blob}
* derived[] {u32 file, tag, meta[4], blob}
* blobs[] {u64 offset, u32 size, u32 zero, u8 sha256[32]}
* u8 table_sha256[32] (everything above), payload.
* Every blob is hashed again on load. Identical bytes share one blob. */
#include "mod_resident.h"
#include "mod_plugins.h"
#include "mod_runtime.h"
#include "psx_sha256.h"
#include <algorithm>
#include <array>
#include <cctype>
#include <chrono>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <filesystem>
#include <fstream>
#include <map>
#include <memory>
#include <stdexcept>
#include <string>
#include <system_error>
#include <vector>
#ifdef _WIN32
#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif
#ifndef NOMINMAX
#define NOMINMAX
#endif
#include <windows.h>
#else
#include <unistd.h>
#endif
namespace {
using Bytes = std::vector<uint8_t>;
using Digest = std::array<uint8_t, 32>;
constexpr char kMagic[8] = {'P', 'S', 'X', 'R', 'E', 'S', '0', '1'};
constexpr uint32_t kVersion = 1;
constexpr uint32_t kBlobAlign = 16;
constexpr uint32_t kFullCd = 360000u * 2048u;
constexpr uint64_t kMaxPackBytes = 1ull << 31;
struct FileRec { uint32_t lba, size, padded, stock, blob; };
struct DerivedRec { uint32_t file, tag, meta[4], blob; };
struct Blob { uint64_t offset; uint32_t size; Digest sha; };
} // namespace
struct PSXResidentPack {
Bytes payload;
std::vector<FileRec> files;
std::vector<DerivedRec> derived;
std::vector<Blob> blobs;
std::vector<uint32_t> by_lba; /* file indices sorted by lba */
uint32_t modified = 0;
};
struct PSXResidentSink {
PSXResidentPack* pack;
std::map<Digest, uint32_t> index;
uint32_t file_count;
std::string error;
};
namespace {
struct Record {
std::string title, format, state, error, path;
std::unique_ptr<PSXResidentPack> pack;
double ms = 0;
};
std::vector<Record>& records() {
static std::vector<Record> r;
return r;
}
Digest sha(const uint8_t* p, size_t n) {
Digest d;
psx_sha256_compute(p, n, d.data());
return d;
}
std::string hex(const uint8_t* d, size_t n = 32) {
std::string out(n * 2, '0');
static const char* digits = "0123456789abcdef";
for (size_t i = 0; i < n; i++) {
out[2 * i] = digits[d[i] >> 4];
out[2 * i + 1] = digits[d[i] & 15];
}
return out;
}
void put32(Bytes& b, uint32_t v) { for (int i = 0; i < 4; i++) b.push_back(uint8_t(v >> (8 * i))); }
void put64(Bytes& b, uint64_t v) { for (int i = 0; i < 8; i++) b.push_back(uint8_t(v >> (8 * i))); }
uint32_t get32(const uint8_t* p) {
return uint32_t(p[0]) | uint32_t(p[1]) << 8 | uint32_t(p[2]) << 16 | uint32_t(p[3]) << 24;
}
uint64_t get64(const uint8_t* p) { return uint64_t(get32(p)) | uint64_t(get32(p + 4)) << 32; }
bool valid_spec(const PSXResidentSpec* s) {
if (!s || s->struct_size < sizeof(PSXResidentSpec) || !s->title || !*s->title ||
!s->format || !*s->format || !s->files || !s->file_count ||
s->policy > PSX_RESIDENT_REQUIRE_STOCK)
return false;
for (const char* p = s->format; *p; ++p)
if (!(std::isalnum((unsigned char)*p) || *p == '-' || *p == '_' || *p == '.')) return false;
for (const char* p = s->title; *p; ++p)
if (*p == '/' || *p == '\\' || *p == ':' || *p == '.') return false;
for (uint32_t i = 0; i < s->file_count; i++) {
const auto& f = s->files[i];
if (!f.path || !*f.path) return false;
if (f.stock_sha256 && std::strlen(f.stock_sha256) != 64) return false;
}
return true;
}
Digest cache_key(const PSXResidentSpec* s, const std::string& fingerprint) {
psx_sha256_ctx ctx;
psx_sha256_init(&ctx);
auto text = [&](const std::string& t) {
psx_sha256_update(&ctx, reinterpret_cast<const uint8_t*>(t.c_str()), t.size() + 1);
};
text("PSXRES01");
text(fingerprint);
text(s->title);
text(s->format);
text(std::to_string(s->policy) + "/" + std::to_string(s->max_file_bytes));
for (uint32_t i = 0; i < s->file_count; i++) {
const auto& f = s->files[i];
text(f.path);
text(std::to_string(f.stock_size));
text(f.stock_sha256 ? f.stock_sha256 : "");
}
Digest d;
psx_sha256_final(&ctx, d.data());
return d;
}
std::filesystem::path cache_dir(const char* title) {
if (const char* p = std::getenv("PSX_RESIDENT_CACHE"))
if (*p) return std::filesystem::path(p) / title;
std::filesystem::path root;
#ifdef _WIN32
if (const char* p = std::getenv("LOCALAPPDATA")) root = p;
#else
if (const char* p = std::getenv("XDG_CACHE_HOME")) root = p;
else if (const char* p = std::getenv("HOME")) root = std::filesystem::path(p) / ".cache";
#endif
if (root.empty()) throw std::runtime_error("no cache directory");
return root / title / "seamless";
}
uint32_t add_blob(PSXResidentSink& sink, const uint8_t* p, uint32_t n) {
const Digest d = sha(p, n);
auto it = sink.index.find(d);
if (it != sink.index.end()) return it->second;
auto& pack = *sink.pack;
uint64_t offset = (pack.payload.size() + kBlobAlign - 1) & ~uint64_t(kBlobAlign - 1);
if (offset + n > kMaxPackBytes) throw std::runtime_error("pack size limit");
pack.payload.resize(size_t(offset));
pack.payload.insert(pack.payload.end(), p, p + n);
pack.blobs.push_back({offset, n, d});
const uint32_t id = uint32_t(pack.blobs.size() - 1);
sink.index.emplace(d, id);
return id;
}
void index_lba(PSXResidentPack& pack) {
pack.by_lba.resize(pack.files.size());
for (uint32_t i = 0; i < pack.by_lba.size(); i++) pack.by_lba[i] = i;
std::sort(pack.by_lba.begin(), pack.by_lba.end(),
[&](uint32_t a, uint32_t b) { return pack.files[a].lba < pack.files[b].lba; });
pack.modified = 0;
for (const auto& f : pack.files) pack.modified += f.stock ? 0 : 1;
}
std::unique_ptr<PSXResidentPack> build(const PSXResidentSpec* s, std::string& error) {
auto pack = std::make_unique<PSXResidentPack>();
PSXResidentSink sink{pack.get(), {}, s->file_count, {}};
const uint32_t max = s->max_file_bytes ? s->max_file_bytes : kFullCd;
Bytes data;
for (uint32_t i = 0; i < s->file_count; i++) {
const auto& f = s->files[i];
uint32_t lba = 0, size = 0;
if (!PSXRecompV4::mod_runtime_read_disc_file_sectors(f.path, max, data, lba, size, &error))
return nullptr;
int stock = 0;
if (f.stock_sha256)
stock = (!f.stock_size || f.stock_size == size) &&
hex(sha(data.data(), data.size()).data()) == f.stock_sha256;
if (!stock && s->policy == PSX_RESIDENT_REQUIRE_STOCK && f.stock_sha256) {
error = std::string(f.path) + ": differs from the original disc";
return nullptr;
}
const uint32_t blob = add_blob(sink, data.data(), uint32_t(data.size()));
pack->files.push_back({lba, size, uint32_t(data.size()), uint32_t(stock), blob});
if (s->derive) {
const size_t before = pack->derived.size();
if (!s->derive(&sink, i, data.data(), uint32_t(data.size()), stock, s->derive_user)) {
error = sink.error.empty() ? std::string(f.path) + ": derive failed" : sink.error;
return nullptr;
}
for (size_t d = before; d < pack->derived.size(); d++)
if (pack->derived[d].file != i) {
error = std::string(f.path) + ": derived blob names another file";
return nullptr;
}
}
}
index_lba(*pack);
return pack;
}
Bytes table(const PSXResidentPack& p, const Digest& key) {
Bytes t(kMagic, kMagic + 8);
put32(t, kVersion);
put32(t, uint32_t(p.files.size()));
put32(t, uint32_t(p.derived.size()));
put32(t, uint32_t(p.blobs.size()));
t.insert(t.end(), key.begin(), key.end());
put64(t, p.payload.size());
for (const auto& f : p.files) {
put32(t, f.lba); put32(t, f.size); put32(t, f.padded); put32(t, f.stock); put32(t, f.blob);
}
for (const auto& d : p.derived) {
put32(t, d.file); put32(t, d.tag);
for (uint32_t m : d.meta) put32(t, m);
put32(t, d.blob);
}
for (const auto& b : p.blobs) {
put64(t, b.offset); put32(t, b.size); put32(t, 0);
t.insert(t.end(), b.sha.begin(), b.sha.end());
}
const Digest d = sha(t.data(), t.size());
t.insert(t.end(), d.begin(), d.end());
return t;
}
void publish(const std::filesystem::path& path, const PSXResidentPack& p, const Digest& key) {
std::filesystem::create_directories(path.parent_path());
auto tmp = path;
#ifdef _WIN32
tmp += "." + std::to_string(GetCurrentProcessId()) + ".tmp";
#else
tmp += "." + std::to_string(getpid()) + ".tmp";
#endif
const Bytes t = table(p, key);
{
std::ofstream out(tmp, std::ios::binary | std::ios::trunc);
out.write(reinterpret_cast<const char*>(t.data()), std::streamsize(t.size()));
out.write(reinterpret_cast<const char*>(p.payload.data()), std::streamsize(p.payload.size()));
out.close();
if (!out) {
std::error_code ec;
std::filesystem::remove(tmp, ec);
throw std::runtime_error("cannot write " + tmp.string());
}
}
#ifdef _WIN32
if (!MoveFileExW(tmp.c_str(), path.c_str(), MOVEFILE_REPLACE_EXISTING | MOVEFILE_WRITE_THROUGH)) {
std::error_code ec;
std::filesystem::remove(tmp, ec);
throw std::runtime_error("cannot publish " + path.string());
}
#else
std::filesystem::rename(tmp, path);
#endif
}
/* Structure, key and every blob hash. Returns null on any mismatch. */
std::unique_ptr<PSXResidentPack> load(const std::filesystem::path& path, const Digest& key,
uint32_t file_count) {
std::error_code ec;
const auto bytes = std::filesystem::file_size(path, ec);
if (ec || bytes < 64 || bytes > kMaxPackBytes) return nullptr;
std::ifstream in(path, std::ios::binary);
uint8_t head[64];
if (!in.read(reinterpret_cast<char*>(head), sizeof head)) return nullptr;
if (std::memcmp(head, kMagic, 8) || get32(head + 8) != kVersion || get32(head + 12) != file_count ||
std::memcmp(head + 24, key.data(), 32))
return nullptr;
const uint64_t nd = get32(head + 16), nb = get32(head + 20), payload = get64(head + 56);
const uint64_t tsize = 64 + uint64_t(file_count) * 20 + nd * 28 + nb * 48;
if (tsize + 32 > bytes || tsize + 32 + payload != bytes) return nullptr;
Bytes raw(static_cast<size_t>(tsize + 32));
std::memcpy(raw.data(), head, sizeof head);
if (!in.read(reinterpret_cast<char*>(raw.data() + 64), std::streamsize(raw.size() - 64))) return nullptr;
const uint8_t* p = raw.data();
if (sha(p, size_t(tsize)) != *reinterpret_cast<const Digest*>(p + tsize)) return nullptr;
auto pack = std::make_unique<PSXResidentPack>();
const uint8_t* q = p + 64;
for (uint32_t i = 0; i < file_count; i++, q += 20)
pack->files.push_back({get32(q), get32(q + 4), get32(q + 8), get32(q + 12), get32(q + 16)});
for (uint64_t i = 0; i < nd; i++, q += 28)
pack->derived.push_back({get32(q), get32(q + 4), {get32(q + 8), get32(q + 12), get32(q + 16),
get32(q + 20)}, get32(q + 24)});
for (uint64_t i = 0; i < nb; i++, q += 48) {
Blob b{get64(q), get32(q + 8), {}};
std::memcpy(b.sha.data(), q + 16, 32);
if (b.offset > payload || b.size > payload - b.offset) return nullptr;
pack->blobs.push_back(b);
}
for (const auto& f : pack->files)
if (f.blob >= nb || pack->blobs[f.blob].size != f.padded || f.padded % 2048 ||
f.size > f.padded || f.padded - f.size >= 2048)
return nullptr;
for (const auto& d : pack->derived)
if (d.blob >= nb || d.file >= file_count) return nullptr;
pack->payload.resize(static_cast<size_t>(payload));
if (!in.read(reinterpret_cast<char*>(pack->payload.data()), std::streamsize(payload))) return nullptr;
for (const auto& b : pack->blobs)
if (sha(pack->payload.data() + b.offset, b.size) != b.sha) return nullptr;
index_lba(*pack);
return pack;
}
/* A cache from another disc with the same plan fingerprint cannot match the
* extents of every listed file on this one. */
bool extents_match(const PSXResidentPack& pack, const PSXResidentSpec* s) {
for (uint32_t i = 0; i < s->file_count; i++) {
uint32_t lba = 0, size = 0;
if (!psx_mod_disc_file_extent(s->files[i].path, &lba, &size) ||
lba != pack.files[i].lba || size != pack.files[i].size)
return false;
}
return true;
}
void prune(const std::filesystem::path& keep, const std::string& format, uint32_t count) {
std::error_code ec;
std::vector<std::filesystem::directory_entry> packs;
const std::string prefix = format + "-";
for (const auto& e : std::filesystem::directory_iterator(keep.parent_path(), ec)) {
const auto name = e.path().filename().string();
if (e.path() != keep && name.rfind(prefix, 0) == 0 && e.path().extension() == ".pack")
packs.push_back(e);
}
if (packs.size() <= count) return;
std::sort(packs.begin(), packs.end(), [](const auto& a, const auto& b) {
std::error_code e1, e2;
return a.last_write_time(e1) > b.last_write_time(e2);
});
for (size_t i = count; i < packs.size(); i++) std::filesystem::remove(packs[i].path(), ec);
}
Record& record_for(const PSXResidentSpec* s) {
auto& r = records();
for (auto& rec : r)
if (rec.title == s->title && rec.format == s->format) return rec;
r.push_back({});
r.back().title = s->title;
r.back().format = s->format;
return r.back();
}
void json_string(std::string& out, const std::string& s) {
out += '"';
for (char c : s) {
if (c == '"' || c == '\\') { out += '\\'; out += c; }
else if ((unsigned char)c < 0x20) { char b[8]; std::snprintf(b, sizeof b, "\\u%04x", c); out += b; }
else out += c;
}
out += '"';
}
} // namespace
extern "C" int psx_resident_emit(PSXResidentSink* sink, uint32_t file, uint32_t tag,
const uint32_t meta[4], const void* bytes, uint32_t size) {
if (!sink || file >= sink->file_count || (!bytes && size)) return 0;
try {
const uint32_t blob = add_blob(*sink, static_cast<const uint8_t*>(bytes), size);
DerivedRec d{file, tag, {0, 0, 0, 0}, blob};
if (meta) std::memcpy(d.meta, meta, sizeof d.meta);
sink->pack->derived.push_back(d);
return 1;
} catch (const std::exception& e) {
sink->error = e.what();
return 0;
}
}
extern "C" const PSXResidentPack* psx_resident_prepare(const PSXResidentSpec* spec) {
if (!valid_spec(spec)) {
psx_mod_counter_add("resident.invalid_spec", 1);
return nullptr;
}
Record& rec = record_for(spec);
rec.pack.reset();
rec.error.clear();
rec.path.clear();
const auto start = std::chrono::steady_clock::now();
try {
const std::string& fingerprint = PSXRecompV4::mod_runtime_fingerprint();
const Digest key = cache_key(spec, fingerprint);
/* Without a committed plan there is no disc identity to key on: build
* in memory and never reuse or publish. */
bool cacheable = !fingerprint.empty();
std::string memory_only; /* why a planned cache is not used */
std::filesystem::path path;
std::unique_ptr<PSXResidentPack> pack;
if (cacheable) {
try {
path = cache_dir(spec->title) / (std::string(spec->format) + "-" + hex(key.data(), 16) + ".pack");
rec.path = path.string();
} catch (const std::exception& e) {
cacheable = false;
memory_only = e.what();
}
}
if (cacheable) {
std::error_code ec;
pack = load(path, key, spec->file_count);
if (pack && !extents_match(*pack, spec)) pack.reset();
if (!pack && std::filesystem::exists(path, ec)) psx_mod_counter_add("resident.cache_rejected", 1);
}
if (pack) {
rec.state = "verified";
std::error_code ec;
std::filesystem::last_write_time(path, std::filesystem::file_time_type::clock::now(), ec);
prune(path, spec->format, spec->keep_packs ? spec->keep_packs : 3);
psx_mod_counter_add("resident.verified", 1);
} else {
pack = build(spec, rec.error);
if (!pack) throw std::runtime_error(rec.error);
/* The cache only shortens the next launch. Whether a pack exists
* depends on the effective disc and the plan alone, never on the
* host file system, so netplay peers with one plan take one path. */
if (cacheable) {
try {
publish(path, *pack, key);
prune(path, spec->format, spec->keep_packs ? spec->keep_packs : 3);
} catch (const std::exception& e) {
memory_only = e.what();
}
}
if (!memory_only.empty()) {
rec.state = "prepared (memory only: " + memory_only + ")";
psx_mod_counter_add("resident.cache_write_failed", 1);
} else {
rec.state = cacheable ? "prepared" : "prepared (uncached: no mod plan)";
}
psx_mod_counter_add("resident.prepared", 1);
}
rec.pack = std::move(pack);
} catch (const std::exception& e) {
rec.pack.reset();
rec.state = "failed";
if (rec.error.empty()) rec.error = e.what();
psx_mod_counter_add("resident.prepare_failed", 1);
}
rec.ms = std::chrono::duration<double, std::milli>(std::chrono::steady_clock::now() - start).count();
return rec.pack.get();
}
extern "C" uint32_t psx_resident_file_count(const PSXResidentPack* p) {
return p ? uint32_t(p->files.size()) : 0;
}
extern "C" const uint8_t* psx_resident_file(const PSXResidentPack* p, uint32_t file,
uint32_t* size, uint32_t* padded) {
if (!p || file >= p->files.size()) return nullptr;
const auto& f = p->files[file];
if (size) *size = f.size;
if (padded) *padded = f.padded;
return p->payload.data() + p->blobs[f.blob].offset;
}
extern "C" uint32_t psx_resident_file_lba(const PSXResidentPack* p, uint32_t file) {
return p && file < p->files.size() ? p->files[file].lba : 0;
}
extern "C" int psx_resident_file_stock(const PSXResidentPack* p, uint32_t file) {
return p && file < p->files.size() ? int(p->files[file].stock) : 0;
}
extern "C" uint32_t psx_resident_modified_files(const PSXResidentPack* p) {
return p ? p->modified : 0;
}
extern "C" const uint8_t* psx_resident_find_lba(const PSXResidentPack* p, uint32_t lba,
uint32_t bytes, uint32_t* file) {
if (!p || p->by_lba.empty()) return nullptr;
/* Last file starting at or before lba. Files never overlap on a disc. */
auto it = std::upper_bound(p->by_lba.begin(), p->by_lba.end(), lba,
[&](uint32_t v, uint32_t i) { return v < p->files[i].lba; });
if (it == p->by_lba.begin()) return nullptr;
const uint32_t i = *--it;
const auto& f = p->files[i];
const uint64_t offset = uint64_t(lba - f.lba) * 2048u;
if (offset > f.padded || bytes > f.padded - offset) return nullptr;
if (file) *file = i;
return p->payload.data() + p->blobs[f.blob].offset + offset;
}
extern "C" uint32_t psx_resident_derived_count(const PSXResidentPack* p) {
return p ? uint32_t(p->derived.size()) : 0;
}
extern "C" const uint8_t* psx_resident_derived(const PSXResidentPack* p, uint32_t index,
uint32_t* file, uint32_t* tag,
uint32_t meta[4], uint32_t* size) {
if (!p || index >= p->derived.size()) return nullptr;
const auto& d = p->derived[index];
if (file) *file = d.file;
if (tag) *tag = d.tag;
if (meta) std::memcpy(meta, d.meta, sizeof d.meta);
if (size) *size = p->blobs[d.blob].size;
return p->payload.data() + p->blobs[d.blob].offset;
}
extern "C" int psx_resident_guest_ranges_match(const PSXResidentRange* ranges, uint32_t count,
const char* sha256) {
if (!ranges || !count || !sha256) return 0;
psx_sha256_ctx ctx;
psx_sha256_init(&ctx);
uint8_t chunk[256];
for (uint32_t r = 0; r < count; r++) {
if (ranges[r].hi < ranges[r].lo) return 0;
for (uint32_t a = ranges[r].lo; a < ranges[r].hi;) {
const uint32_t n = std::min<uint32_t>(sizeof chunk, ranges[r].hi - a);
for (uint32_t i = 0; i < n; i++) chunk[i] = psx_mod_read_byte(a + i);
psx_sha256_update(&ctx, chunk, n);
a += n;
}
}
uint8_t d[32];
psx_sha256_final(&ctx, d);
return hex(d) == sha256;
}
extern "C" int psx_resident_status_json(char* out, uint32_t capacity) {
std::string s = "[";
for (const auto& r : records()) {
if (s.size() > 1) s += ',';
s += "{\"title\":"; json_string(s, r.title);
s += ",\"format\":"; json_string(s, r.format);
s += ",\"state\":"; json_string(s, r.state);
s += ",\"error\":"; json_string(s, r.error);
s += ",\"path\":"; json_string(s, r.path);
char b[256];
const PSXResidentPack* p = r.pack.get();
std::snprintf(b, sizeof b,
",\"files\":%u,\"modified\":%u,\"derived\":%u,\"blobs\":%u,\"bytes\":%llu,\"ms\":%.1f}",
p ? unsigned(p->files.size()) : 0u, p ? p->modified : 0u,
p ? unsigned(p->derived.size()) : 0u, p ? unsigned(p->blobs.size()) : 0u,
p ? (unsigned long long)p->payload.size() : 0ull, r.ms);
s += b;
}
s += ']';
if (!out || capacity <= s.size()) return 0;
std::memcpy(out, s.c_str(), s.size() + 1);
return 1;
}
/* Always-on service ring (mod_resident.h). Frames come from the debug
* server's guest frame counter, the clock of the CD-ROM rings, so a load
* window can be compared with cdrom_bursts / cdrom_sector_history. */
extern "C" uint64_t s_frame_count;
extern "C" uint64_t psx_get_cycle_count(void);
namespace {
struct Event {
uint64_t seq, frame, cycle;
const char* op;
uint32_t file, lba, bytes, served;
};
constexpr uint32_t kEventCapacity = 8192;
Event g_events[kEventCapacity];
uint64_t g_event_total = 0;
} // namespace
extern "C" void psx_resident_record(const char* op, uint32_t file, uint32_t lba,
uint32_t bytes, int served) {
Event& e = g_events[g_event_total % kEventCapacity];
e.seq = g_event_total++;
e.frame = s_frame_count;
e.cycle = psx_get_cycle_count();
e.op = op && *op ? op : "?";
e.file = file;
e.lba = lba;
e.bytes = bytes;
e.served = served ? 1u : 0u;
}
extern "C" int psx_resident_events_json(char* out, uint32_t capacity, uint64_t frame_lo,
uint64_t frame_hi, uint32_t max) {
const uint64_t held = std::min<uint64_t>(g_event_total, kEventCapacity);
std::vector<const Event*> picked;
for (uint64_t i = 0; i < held && picked.size() < max; i++) {
const Event& e = g_events[(g_event_total - 1 - i) % kEventCapacity];
if (e.frame >= frame_lo && e.frame <= frame_hi) picked.push_back(&e);
}
std::string s;
char b[96];
std::snprintf(b, sizeof b, "{\"total\":%llu,\"capacity\":%u,\"entries\":[",
(unsigned long long)g_event_total, kEventCapacity);
s += b;
for (size_t i = picked.size(); i-- > 0;) {
const Event& e = *picked[i];
s += "{\"seq\":" + std::to_string(e.seq) + ",\"frame\":" + std::to_string(e.frame) +
",\"cycle\":" + std::to_string(e.cycle) + ",\"op\":";
json_string(s, e.op);
std::snprintf(b, sizeof b, ",\"file\":%d,\"lba\":%u,\"bytes\":%u,\"served\":%u}%s",
e.file == UINT32_MAX ? -1 : int(e.file), e.lba, e.bytes, e.served,
i ? "," : "");
s += b;
}
s += "]}";
if (!out || capacity <= s.size()) return 0;
std::memcpy(out, s.c_str(), s.size() + 1);
return 1;
}
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