108 lines
2.7 KiB
Go
108 lines
2.7 KiB
Go
//go:build !windows
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// +build !windows
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package lockfile
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import (
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"time"
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"github.com/containers/storage/pkg/system"
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"golang.org/x/sys/unix"
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)
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type fileHandle uintptr
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// GetLastWrite returns a LastWrite value corresponding to current state of the lock.
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// This is typically called before (_not after_) loading the state when initializing a consumer
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// of the data protected by the lock.
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// During the lifetime of the consumer, the consumer should usually call ModifiedSince instead.
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//
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// The caller must hold the lock (for reading or writing).
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func (l *LockFile) GetLastWrite() (LastWrite, error) {
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l.AssertLocked()
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contents := make([]byte, lastWriterIDSize)
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n, err := unix.Pread(int(l.fd), contents, 0)
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if err != nil {
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return LastWrite{}, err
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}
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// It is important to handle the partial read case, because
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// the initial size of the lock file is zero, which is a valid
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// state (no writes yet)
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contents = contents[:n]
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return newLastWriteFromData(contents), nil
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}
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// RecordWrite updates the lock with a new LastWrite value, and returns the new value.
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//
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// If this function fails, the LastWriter value of the lock is indeterminate;
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// the caller should keep using the previously-recorded LastWrite value,
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// and possibly detecting its own modification as an external one:
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//
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// lw, err := state.lock.RecordWrite()
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// if err != nil { /* fail */ }
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// state.lastWrite = lw
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//
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// The caller must hold the lock for writing.
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func (l *LockFile) RecordWrite() (LastWrite, error) {
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l.AssertLockedForWriting()
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lw := newLastWrite()
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lockContents := lw.serialize()
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n, err := unix.Pwrite(int(l.fd), lockContents, 0)
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if err != nil {
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return LastWrite{}, err
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}
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if n != len(lockContents) {
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return LastWrite{}, unix.ENOSPC
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}
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return lw, nil
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}
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// TouchedSince indicates if the lock file has been touched since the specified time
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func (l *LockFile) TouchedSince(when time.Time) bool {
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st, err := system.Fstat(int(l.fd))
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if err != nil {
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return true
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}
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mtim := st.Mtim()
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touched := time.Unix(mtim.Unix())
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return when.Before(touched)
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}
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func openHandle(path string, mode int) (fileHandle, error) {
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mode |= unix.O_CLOEXEC
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fd, err := unix.Open(path, mode, 0o644)
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return fileHandle(fd), err
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}
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func lockHandle(fd fileHandle, lType lockType, nonblocking bool) error {
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fType := unix.F_RDLCK
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if lType != readLock {
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fType = unix.F_WRLCK
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}
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lk := unix.Flock_t{
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Type: int16(fType),
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Whence: int16(unix.SEEK_SET),
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Start: 0,
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Len: 0,
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}
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cmd := unix.F_SETLKW
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if nonblocking {
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cmd = unix.F_SETLK
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}
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for {
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err := unix.FcntlFlock(uintptr(fd), cmd, &lk)
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if err == nil || nonblocking {
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return err
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}
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time.Sleep(10 * time.Millisecond)
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}
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}
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func unlockAndCloseHandle(fd fileHandle) {
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unix.Close(int(fd))
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}
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func closeHandle(fd fileHandle) {
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unix.Close(int(fd))
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}
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