103 lines
2.6 KiB
Go
103 lines
2.6 KiB
Go
package dirivcache
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import (
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"log"
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"strings"
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"sync"
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"time"
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)
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const (
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maxEntries = 100
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expireTime = 1 * time.Second
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)
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type cacheEntry struct {
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// DirIV of the directory.
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iv []byte
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// Relative ciphertext path of the directory.
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cDir string
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}
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// DirIVCache stores up to "maxEntries" directory IVs.
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type DirIVCache struct {
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// data in the cache, indexed by relative plaintext path
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// of the directory.
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data map[string]cacheEntry
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// The DirIV of the root directory gets special treatment because it
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// cannot change (the root directory cannot be renamed or deleted).
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// It is unaffected by the expiry timer and cache clears.
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rootDirIV []byte
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// expiry is the time when the whole cache expires.
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// The cached entry my become out-of-date if the ciphertext directory is
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// modifed behind the back of gocryptfs. Having an expiry time limits the
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// inconstency to one second, like attr_timeout does for the kernel
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// getattr cache.
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expiry time.Time
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sync.RWMutex
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}
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// Lookup - fetch entry for "dir" (relative plaintext path) from the cache.
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// Returns the directory IV and the relative encrypted path, or (nil, "")
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// if the entry was not found.
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func (c *DirIVCache) Lookup(dir string) (iv []byte, cDir string) {
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c.RLock()
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defer c.RUnlock()
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if dir == "" {
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return c.rootDirIV, ""
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}
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if c.data == nil {
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return nil, ""
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}
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if time.Since(c.expiry) > 0 {
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c.data = nil
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return nil, ""
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}
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v := c.data[dir]
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return v.iv, v.cDir
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}
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// Store - write an entry for directory "dir" into the cache.
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// Arguments:
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// dir ... relative plaintext path
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// iv .... directory IV
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// cDir .. relative ciphertext path
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func (c *DirIVCache) Store(dir string, iv []byte, cDir string) {
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c.Lock()
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defer c.Unlock()
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if dir == "" {
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c.rootDirIV = iv
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}
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// Sanity check: plaintext and chiphertext paths must have the same number
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// of segments
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if strings.Count(dir, "/") != strings.Count(cDir, "/") {
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log.Panicf("inconsistent number of path segments: dir=%q cDir=%q", dir, cDir)
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}
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// Clear() may have cleared c.data: re-initialize
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if c.data == nil {
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c.data = make(map[string]cacheEntry, maxEntries)
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// Set expiry time one second into the future
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c.expiry = time.Now().Add(expireTime)
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}
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// Delete a random entry from the map if reached maxEntries
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if len(c.data) >= maxEntries {
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for k := range c.data {
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delete(c.data, k)
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break
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}
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}
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c.data[dir] = cacheEntry{iv, cDir}
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}
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// Clear ... clear the cache.
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// Called from fusefrontend when directories are renamed or deleted.
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func (c *DirIVCache) Clear() {
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c.Lock()
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defer c.Unlock()
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// Will be re-initialized in the next Store()
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c.data = nil
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}
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