parent
89966b1aae
commit
71eb2bdf7c
GPG Key ID:
AFE384344A45E13A
@ -0,0 +1,136 @@
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package main
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import (
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"log"
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"syscall"
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"time"
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)
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const (
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// Number of entries in the dirCache.
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// 20 entries work well for "git stat" on a small git repo on sshfs.
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// Keep in sync with test_helpers.maxCacheFds !
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// TODO: How to share this constant without causing an import cycle?
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dirCacheSize = 20
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// Enable Lookup/Store/Clear debug messages
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enableDebugMessages = false
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// Enable hit rate statistics printing
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enableStats = false
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)
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type dirCacheEntry struct {
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path string
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// fd to the directory (opened with O_PATH!)
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fd int
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// content of gocryptfs.diriv in this directory
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iv []byte
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}
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func (e *dirCacheEntry) Clear() {
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// An earlier clear may have already closed the fd, or the cache
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// has never been filled (fd is 0 in that case).
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// Note: package ensurefds012, imported from main, guarantees that dirCache
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// can never get fds 0,1,2.
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if e.fd > 0 {
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syscall.Close(e.fd)
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}
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e.fd = -1
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e.path = ""
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e.iv = nil
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}
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type dirCache struct {
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// Expected length of the stored IVs. Only used for sanity checks.
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// Usually set to 16, but 0 in plaintextnames mode.
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ivLen int
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// Cache entries
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entries [dirCacheSize]dirCacheEntry
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// Where to store the next entry (index into entries)
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nextIndex int
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// On the first Lookup(), the expire thread is started, and this flag is set
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// to true.
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expireThreadRunning bool
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// Hit rate stats. Evaluated and reset by the expire thread.
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lookups uint64
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hits uint64
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}
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// Clear clears the cache contents.
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func (d *dirCache) Clear() {
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for i := range d.entries {
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d.entries[i].Clear()
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}
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}
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// Store the entry in the cache. The passed "fd" will be Dup()ed, and the caller
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// can close their copy at will.
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func (d *dirCache) Store(path string, fd int, iv []byte) {
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// Note: package ensurefds012, imported from main, guarantees that dirCache
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// can never get fds 0,1,2.
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if fd <= 0 || len(iv) != d.ivLen {
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log.Panicf("Store sanity check failed: fd=%d len=%d", fd, len(iv))
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}
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e := &d.entries[d.nextIndex]
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// Round-robin works well enough
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d.nextIndex = (d.nextIndex + 1) % dirCacheSize
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// Close the old fd
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e.Clear()
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fd2, err := syscall.Dup(fd)
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if err != nil {
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return
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}
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e.fd = fd2
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e.path = string([]byte(path[:]))
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e.iv = iv
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// expireThread is started on the first Lookup()
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if !d.expireThreadRunning {
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d.expireThreadRunning = true
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go d.expireThread()
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}
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}
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// Lookup checks if relPath is in the cache, and returns an (fd, iv) pair.
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// It returns (-1, nil) if not found. The fd is internally Dup()ed and the
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// caller must close it when done.
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func (d *dirCache) Lookup(path string) (fd int, iv []byte) {
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if enableStats {
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d.lookups++
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}
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var e *dirCacheEntry
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for i := range d.entries {
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e = &d.entries[i]
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if e.fd <= 0 {
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// Cache slot is empty
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continue
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}
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if path != e.path {
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// Not the right path
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continue
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}
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var err error
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fd, err = syscall.Dup(e.fd)
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if err != nil {
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return -1, nil
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}
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iv = e.iv
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break
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}
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if fd == 0 {
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return -1, nil
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}
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if enableStats {
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d.hits++
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}
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if fd <= 0 || len(iv) != d.ivLen {
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log.Panicf("Lookup sanity check failed: fd=%d len=%d", fd, len(iv))
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}
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return fd, iv
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}
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// expireThread is started on the first Lookup()
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func (d *dirCache) expireThread() {
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for {
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time.Sleep(60 * time.Second)
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d.Clear()
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}
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}
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