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package fusefrontend
import (
"golang.org/x/sys/unix"
"github.com/rfjakob/gocryptfs/v2/internal/syscallcompat"
"github.com/rfjakob/gocryptfs/v2/internal/tlog"
)
// SharedStorageLock conveniently wraps F_OFD_SETLKW.
// It is a no-op unless args.SharedStorage is set.
//
// See https://man7.org/linux/man-pages/man2/fcntl.2.html -> "Open file description locks (non-POSIX)"
//
// lkType is one of:
// * unix.F_RDLCK (shared read lock)
// * unix.F_WRLCK (exclusive write lock)
// * unix.F_UNLCK (unlock)
//
// This function is a no-op if args.SharedStorage == false.
func (f *File) LockSharedStorage(lkType int16, lkStart int64, lkLen int64) (err error) {
if !f.rootNode.args.SharedStorage {
return nil
}
lk := unix.Flock_t{
Type: lkType,
Whence: unix.SEEK_SET,
Start: lkStart,
Len: lkLen,
}
err = unix.FcntlFlock(uintptr(f.intFd()), syscallcompat.F_OFD_SETLK, &lk)
switch err {
case unix.EACCES, unix.EAGAIN:
tlog.Debug.Printf("LockSharedStorage: waiting for lock")
case nil:
return
}
for {
err = unix.FcntlFlock(uintptr(f.intFd()), syscallcompat.F_OFD_SETLKW, &lk)
if err == unix.EINTR {
tlog.Debug.Printf("LockSharedStorage: looping on EINTR")
continue
}
return
}
}
// UnlockSharedStorage calls LockSharedStorage with unix.F_UNLCK.
func (f *File) UnlockSharedStorage(lkStart int64, lkLen int64) error {
return f.LockSharedStorage(unix.F_UNLCK, lkStart, lkLen)
}
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