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