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// Copyright 2025 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
package aflow
import (
"fmt"
"maps"
"os"
"path/filepath"
"slices"
"sync"
"testing"
"time"
"github.com/google/syzkaller/pkg/hash"
"github.com/google/syzkaller/pkg/osutil"
)
// Cache maintains on-disk cache with directories with arbitrary contents (kernel checkouts, builds, etc).
// Create method is used to either create a new directory, if it's not cached yet, or returns a previously
// cached directory. Old unused directories are incrementally removed if the total disk usage grows
// over the specified limit.
type Cache struct {
dir string
maxSize uint64
timeNow func() time.Time
t *testing.T
mu sync.Mutex
currentSize uint64
entries map[string]*cacheEntry
}
type cacheEntry struct {
dir string
size uint64
usageCount int
lastUsed time.Time
}
func NewCache(dir string, maxSize uint64) (*Cache, error) {
return newTestCache(nil, dir, maxSize, time.Now)
}
func newTestCache(t *testing.T, dir string, maxSize uint64, timeNow func() time.Time) (*Cache, error) {
if dir == "" {
return nil, fmt.Errorf("cache workdir is empty")
}
c := &Cache{
dir: osutil.Abs(dir),
maxSize: maxSize,
timeNow: timeNow,
t: t,
entries: make(map[string]*cacheEntry),
}
if err := c.init(); err != nil {
return nil, err
}
return c, nil
}
// Create creates/returns a cached directory with contents created by the populate callback.
// The populate callback receives a dir it needs to populate with cached files.
// The typ must be a short descriptive name of the contents (e.g. "build", "source", etc).
// The desc is used to identify cached entries and must fully describe the cached contents
// (the second invocation with the same typ+desc will return dir created by the first
// invocation with the same typ+desc).
func (c *Cache) Create(typ, desc string, populate func(string) error) (string, error) {
c.mu.Lock()
defer c.mu.Unlock()
// Note: we don't populate a temp dir and then atomically rename it to the final destination,
// because at least kernel builds encode the current path in debug info/compile commands,
// so moving the dir later would break all that. Instead we rely on the presence of the meta file
// to denote valid cache entries. Modification time of the file says when it was last used.
id := hash.String(desc)
dir := filepath.Join(c.dir, typ, id)
metaFile := filepath.Join(dir, cacheMetaFile)
if c.entries[dir] == nil {
os.RemoveAll(dir)
if err := osutil.MkdirAll(dir); err != nil {
return "", err
}
if err := populate(dir); err != nil {
os.RemoveAll(dir)
return "", err
}
size, err := osutil.DiskUsage(dir)
if err != nil {
return "", err
}
if err := osutil.WriteFile(metaFile, []byte(desc)); err != nil {
os.RemoveAll(dir)
return "", err
}
c.entries[dir] = &cacheEntry{
dir: dir,
size: size,
}
c.currentSize += size
c.logf("created entry %v, size %v, current size %v", dir, size, c.currentSize)
}
// Note the entry was used now.
now := c.timeNow()
if err := os.Chtimes(metaFile, now, now); err != nil {
return "", err
}
entry := c.entries[dir]
entry.usageCount++
entry.lastUsed = now
c.logf("using entry %v, usage count %v", dir, entry.usageCount)
if err := c.purge(); err != nil {
entry.usageCount--
return "", err
}
return dir, nil
}
// Release must be called for every directory returned by Create method when the directory is not used anymore.
func (c *Cache) Release(dir string) {
c.mu.Lock()
defer c.mu.Unlock()
entry := c.entries[dir]
entry.usageCount--
c.logf("release entry %v, usage count %v", dir, entry.usageCount)
if entry.usageCount < 0 {
panic("negative usageCount")
}
}
// init reads the cached dirs (disk usage, last use time) from disk when the cache is created.
func (c *Cache) init() error {
dirs, err := filepath.Glob(filepath.Join(c.dir, "*", "*"))
if err != nil {
return err
}
for _, dir := range dirs {
metaFile := filepath.Join(dir, cacheMetaFile)
if !osutil.IsExist(metaFile) {
if err := osutil.RemoveAll(dir); err != nil {
return err
}
continue
}
stat, err := os.Stat(metaFile)
if err != nil {
return err
}
size, err := osutil.DiskUsage(dir)
if err != nil {
return err
}
c.entries[dir] = &cacheEntry{
dir: dir,
size: size,
lastUsed: stat.ModTime(),
}
c.currentSize += size
}
c.mu.Lock()
defer c.mu.Unlock()
return c.purge()
}
// purge removes oldest unused directories if the cache is over maxSize.
func (c *Cache) purge() error {
if c.mu.TryLock() {
panic("c.mu is not locked")
}
if c.currentSize < c.maxSize {
return nil
}
list := slices.Collect(maps.Values(c.entries))
slices.SortFunc(list, func(a, b *cacheEntry) int {
if a.usageCount != b.usageCount {
return a.usageCount - b.usageCount
}
return a.lastUsed.Compare(b.lastUsed)
})
for _, entry := range list {
if entry.usageCount != 0 || c.currentSize < c.maxSize {
break
}
if err := os.RemoveAll(entry.dir); err != nil {
return err
}
delete(c.entries, entry.dir)
if c.currentSize < entry.size {
panic(fmt.Sprintf("negative currentSize: %v %v", c.currentSize, entry.size))
}
c.currentSize -= entry.size
}
return nil
}
func (c *Cache) logf(msg string, args ...any) {
if c.t != nil {
c.t.Logf("cache: "+msg, args...)
}
}
const cacheMetaFile = "aflow-meta"
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