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