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80 lines
2.3 KiB
C++
80 lines
2.3 KiB
C++
#include "access_rx_cache.h"
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#include "io_uring_engine.h"
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include <utility>
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using namespace std;
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void AccessRXCache::check_access(const char *filename, bool allow_async, function<void(bool)> cb)
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{
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if (!check_visibility) {
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cb(true);
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return;
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}
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lock_guard<mutex> lock(mu);
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if (engine == nullptr || !engine->get_supports_stat()) {
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allow_async = false;
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}
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for (const char *end = strchr(filename + 1, '/'); end != nullptr; end = strchr(end + 1, '/')) {
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string parent_path(filename, end - filename); // string_view from C++20.
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auto cache_it = cache.find(parent_path);
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if (cache_it != cache.end()) {
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// Found in the cache.
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if (!cache_it->second) {
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cb(false);
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return;
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}
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continue;
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}
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if (!allow_async) {
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bool ok = access(parent_path.c_str(), R_OK | X_OK) == 0;
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cache.emplace(parent_path, ok);
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if (!ok) {
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cb(false);
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return;
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}
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continue;
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}
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// We want to call access(), but it could block on I/O. io_uring doesn't support
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// access(), but we can do a dummy asynchonous statx() to populate the kernel's cache,
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// which nearly always makes the next access() instantaneous.
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// See if there's already a pending stat that matches this,
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// or is a subdirectory.
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auto it = pending_stats.lower_bound(parent_path);
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if (it != pending_stats.end() && it->first.size() >= parent_path.size() &&
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it->first.compare(0, parent_path.size(), parent_path) == 0) {
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it->second.emplace_back(PendingStat{ filename, move(cb) });
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} else {
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it = pending_stats.emplace(filename, vector<PendingStat>{}).first;
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engine->submit_stat(filename, [this, it, filename{ strdup(filename) }, cb{ move(cb) }](bool) {
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// The stat returned, so now do the actual access() calls.
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// All of them should be in cache, so don't fire off new statx()
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// calls during that check.
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check_access(filename, /*allow_async=*/false, move(cb));
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free(filename);
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// Call all others that waited for the same stat() to finish.
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// They may fire off new stat() calls if needed.
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vector<PendingStat> pending = move(it->second);
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pending_stats.erase(it);
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for (PendingStat &ps : pending) {
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check_access(ps.filename.c_str(), /*allow_async=*/true, move(ps.cb));
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}
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});
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}
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return; // The rest will happen in async context.
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}
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// Passed all checks.
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cb(true);
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}
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