Re-design of the original gocryptfs code to work as a library.
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package main
import (
"log"
"sync"
"syscall"
"time"
)
const (
// Number of entries in the dirCache.
// 20 entries work well for "git stat" on a small git repo on sshfs.
// Keep in sync with test_helpers.maxCacheFds !
// TODO: How to share this constant without causing an import cycle?
dirCacheSize = 20
// Enable Lookup/Store/Clear debug messages
enableDebugMessages = false
// Enable hit rate statistics printing
enableStats = false
)
type dirCacheEntry struct {
path string
// fd to the directory (opened with O_PATH!)
fd int
// content of gocryptfs.diriv in this directory
iv []byte
}
func (e *dirCacheEntry) Clear() {
// An earlier clear may have already closed the fd, or the cache
// has never been filled (fd is 0 in that case).
// Note: package ensurefds012, imported from main, guarantees that dirCache
// can never get fds 0,1,2.
if e.fd > 0 {
syscall.Close(e.fd)
}
e.fd = -1
e.path = ""
e.iv = nil
}
type dirCache struct {
sync.Mutex
// Expected length of the stored IVs. Only used for sanity checks.
// Usually set to 16, but 0 in plaintextnames mode.
ivLen int
// Cache entries
entries [dirCacheSize]dirCacheEntry
// Where to store the next entry (index into entries)
nextIndex int
// On the first Lookup(), the expire thread is started, and this flag is set
// to true.
expireThreadRunning bool
// Hit rate stats. Evaluated and reset by the expire thread.
lookups uint64
hits uint64
}
// Clear clears the cache contents.
func (d *dirCache) Clear() {
d.Lock()
defer d.Unlock()
for i := range d.entries {
d.entries[i].Clear()
}
}
// Store the entry in the cache. The passed "fd" will be Dup()ed, and the caller
// can close their copy at will.
func (d *dirCache) Store(path string, fd int, iv []byte) {
// Note: package ensurefds012, imported from main, guarantees that dirCache
// can never get fds 0,1,2.
if fd <= 0 || len(iv) != d.ivLen {
log.Panicf("Store sanity check failed: fd=%d len=%d", fd, len(iv))
}
d.Lock()
defer d.Unlock()
e := &d.entries[d.nextIndex]
// Round-robin works well enough
d.nextIndex = (d.nextIndex + 1) % dirCacheSize
// Close the old fd
e.Clear()
fd2, err := syscall.Dup(fd)
if err != nil {
return
}
e.fd = fd2
e.path = string([]byte(path[:]))
e.iv = iv
// expireThread is started on the first Lookup()
if !d.expireThreadRunning {
d.expireThreadRunning = true
go d.expireThread()
}
}
// Lookup checks if relPath is in the cache, and returns an (fd, iv) pair.
// It returns (-1, nil) if not found. The fd is internally Dup()ed and the
// caller must close it when done.
func (d *dirCache) Lookup(path string) (fd int, iv []byte) {
d.Lock()
defer d.Unlock()
if enableStats {
d.lookups++
}
var e *dirCacheEntry
for i := range d.entries {
e = &d.entries[i]
if e.fd <= 0 {
// Cache slot is empty
continue
}
if path != e.path {
// Not the right path
continue
}
var err error
fd, err = syscall.Dup(e.fd)
if err != nil {
return -1, nil
}
iv = e.iv
break
}
if fd == 0 {
return -1, nil
}
if enableStats {
d.hits++
}
if fd <= 0 || len(iv) != d.ivLen {
log.Panicf("Lookup sanity check failed: fd=%d len=%d", fd, len(iv))
}
return fd, iv
}
// expireThread is started on the first Lookup()
func (d *dirCache) expireThread() {
for {
time.Sleep(60 * time.Second)
d.Clear()
}
}
func (d* dirCache) Delete(path string) {
for i := range d.entries {
e := &d.entries[i]
if e.path == path {
e.Clear()
break
}
}
}