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authorJakob Unterwurzacher2017-04-02 21:32:01 +0200
committerJakob Unterwurzacher2017-04-29 22:24:38 +0200
commit863c3ca36fe756767ad2f86348a0646f2e7a09a5 (patch)
tree90c50a9296f828cdd9323bde6bdea242eb14571a /internal/fusefrontend/open_file_table.go
parentd20290671e2157162e608c43230fb6c51abfbc94 (diff)
fusefrontend: rename write_lock.go -> open_file_table.go
The data structure was originally called write lock table, but is now simply called the open file table. Rename the file to reflect that.
Diffstat (limited to 'internal/fusefrontend/open_file_table.go')
-rw-r--r--internal/fusefrontend/open_file_table.go101
1 files changed, 101 insertions, 0 deletions
diff --git a/internal/fusefrontend/open_file_table.go b/internal/fusefrontend/open_file_table.go
new file mode 100644
index 0000000..053298d
--- /dev/null
+++ b/internal/fusefrontend/open_file_table.go
@@ -0,0 +1,101 @@
+package fusefrontend
+
+import (
+ "sync"
+ "sync/atomic"
+ "syscall"
+)
+
+// DevInoStruct uniquely identifies a backing file through device number and
+// inode number.
+type DevInoStruct struct {
+ dev uint64
+ ino uint64
+}
+
+// DevInoFromStat fills a new DevInoStruct with the passed Stat_t info
+func DevInoFromStat(st *syscall.Stat_t) DevInoStruct {
+ // Explicit cast to uint64 to prevent build problems on 32-bit platforms
+ return DevInoStruct{
+ dev: uint64(st.Dev),
+ ino: uint64(st.Ino),
+ }
+}
+
+func init() {
+ openFileMap.entries = make(map[DevInoStruct]*openFileEntryT)
+}
+
+// wlock - serializes write accesses to each file (identified by inode number)
+// Writing partial blocks means we have to do read-modify-write cycles. We
+// really don't want concurrent writes there.
+// Concurrent full-block writes could actually be allowed, but are not to
+// keep the locking simple.
+var openFileMap openFileMapT
+
+// wlockMap - usage:
+// 1) register
+// 2) lock ... unlock ...
+// 3) unregister
+type openFileMapT struct {
+ // opCount counts writeLock.Lock() calls. As every operation that modifies a file should
+ // call it, this effectively serves as a write-operation counter.
+ // The variable is accessed without holding any locks so atomic operations
+ // must be used. It must be the first element of the struct to guarantee
+ // 64-bit alignment.
+ opCount uint64
+ // Protects map access
+ sync.Mutex
+ entries map[DevInoStruct]*openFileEntryT
+}
+
+type opCountMutex struct {
+ sync.Mutex
+ // Points to the opCount variable of the parent openFileMapT
+ opCount *uint64
+}
+
+func (o *opCountMutex) Lock() {
+ o.Mutex.Lock()
+ atomic.AddUint64(o.opCount, 1)
+}
+
+// refCntMutex - mutex with reference count
+type openFileEntryT struct {
+ // Reference count
+ refCnt int
+ // Write lock for this inode
+ writeLock *opCountMutex
+ // ID is the file ID in the file header.
+ ID []byte
+ IDLock sync.RWMutex
+}
+
+// register creates an entry for "ino", or incrementes the reference count
+// if the entry already exists.
+func (w *openFileMapT) register(di DevInoStruct) *openFileEntryT {
+ w.Lock()
+ defer w.Unlock()
+
+ r := w.entries[di]
+ if r == nil {
+ o := opCountMutex{opCount: &w.opCount}
+ r = &openFileEntryT{writeLock: &o}
+ w.entries[di] = r
+ }
+ r.refCnt++
+ return r
+}
+
+// unregister decrements the reference count for "di" and deletes the entry if
+// the reference count has reached 0.
+func (w *openFileMapT) unregister(di DevInoStruct) {
+ w.Lock()
+ defer w.Unlock()
+
+ r := w.entries[di]
+ r.refCnt--
+ if r.refCnt == 0 {
+ delete(w.entries, di)
+ }
+}