vendor: add buildkit

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/gofrs/flock/flock_unix.go

@@ -0,0 +1,195 @@
+// Copyright 2015 Tim Heckman. All rights reserved.
+// Use of this source code is governed by the BSD 3-Clause
+// license that can be found in the LICENSE file.
+
+// +build !windows
+
+package flock
+
+import (
+	"os"
+	"syscall"
+)
+
+// Lock is a blocking call to try and take an exclusive file lock. It will wait
+// until it is able to obtain the exclusive file lock. It's recommended that
+// TryLock() be used over this function. This function may block the ability to
+// query the current Locked() or RLocked() status due to a RW-mutex lock.
+//
+// If we are already exclusive-locked, this function short-circuits and returns
+// immediately assuming it can take the mutex lock.
+//
+// If the *Flock has a shared lock (RLock), this may transparently replace the
+// shared lock with an exclusive lock on some UNIX-like operating systems. Be
+// careful when using exclusive locks in conjunction with shared locks
+// (RLock()), because calling Unlock() may accidentally release the exclusive
+// lock that was once a shared lock.
+func (f *Flock) Lock() error {
+	return f.lock(&f.l, syscall.LOCK_EX)
+}
+
+// RLock is a blocking call to try and take a shared file lock. It will wait
+// until it is able to obtain the shared file lock. It's recommended that
+// TryRLock() be used over this function. This function may block the ability to
+// query the current Locked() or RLocked() status due to a RW-mutex lock.
+//
+// If we are already shared-locked, this function short-circuits and returns
+// immediately assuming it can take the mutex lock.
+func (f *Flock) RLock() error {
+	return f.lock(&f.r, syscall.LOCK_SH)
+}
+
+func (f *Flock) lock(locked *bool, flag int) error {
+	f.m.Lock()
+	defer f.m.Unlock()
+
+	if *locked {
+		return nil
+	}
+
+	if f.fh == nil {
+		if err := f.setFh(); err != nil {
+			return err
+		}
+	}
+
+	if err := syscall.Flock(int(f.fh.Fd()), flag); err != nil {
+		shouldRetry, reopenErr := f.reopenFDOnError(err)
+		if reopenErr != nil {
+			return reopenErr
+		}
+
+		if !shouldRetry {
+			return err
+		}
+
+		if err = syscall.Flock(int(f.fh.Fd()), flag); err != nil {
+			return err
+		}
+	}
+
+	*locked = true
+	return nil
+}
+
+// Unlock is a function to unlock the file. This file takes a RW-mutex lock, so
+// while it is running the Locked() and RLocked() functions will be blocked.
+//
+// This function short-circuits if we are unlocked already. If not, it calls
+// syscall.LOCK_UN on the file and closes the file descriptor. It does not
+// remove the file from disk. It's up to your application to do.
+//
+// Please note, if your shared lock became an exclusive lock this may
+// unintentionally drop the exclusive lock if called by the consumer that
+// believes they have a shared lock. Please see Lock() for more details.
+func (f *Flock) Unlock() error {
+	f.m.Lock()
+	defer f.m.Unlock()
+
+	// if we aren't locked or if the lockfile instance is nil
+	// just return a nil error because we are unlocked
+	if (!f.l && !f.r) || f.fh == nil {
+		return nil
+	}
+
+	// mark the file as unlocked
+	if err := syscall.Flock(int(f.fh.Fd()), syscall.LOCK_UN); err != nil {
+		return err
+	}
+
+	f.fh.Close()
+
+	f.l = false
+	f.r = false
+	f.fh = nil
+
+	return nil
+}
+
+// TryLock is the preferred function for taking an exclusive file lock. This
+// function takes an RW-mutex lock before it tries to lock the file, so there is
+// the possibility that this function may block for a short time if another
+// goroutine is trying to take any action.
+//
+// The actual file lock is non-blocking. If we are unable to get the exclusive
+// file lock, the function will return false instead of waiting for the lock. If
+// we get the lock, we also set the *Flock instance as being exclusive-locked.
+func (f *Flock) TryLock() (bool, error) {
+	return f.try(&f.l, syscall.LOCK_EX)
+}
+
+// TryRLock is the preferred function for taking a shared file lock. This
+// function takes an RW-mutex lock before it tries to lock the file, so there is
+// the possibility that this function may block for a short time if another
+// goroutine is trying to take any action.
+//
+// The actual file lock is non-blocking. If we are unable to get the shared file
+// lock, the function will return false instead of waiting for the lock. If we
+// get the lock, we also set the *Flock instance as being share-locked.
+func (f *Flock) TryRLock() (bool, error) {
+	return f.try(&f.r, syscall.LOCK_SH)
+}
+
+func (f *Flock) try(locked *bool, flag int) (bool, error) {
+	f.m.Lock()
+	defer f.m.Unlock()
+
+	if *locked {
+		return true, nil
+	}
+
+	if f.fh == nil {
+		if err := f.setFh(); err != nil {
+			return false, err
+		}
+	}
+
+	var retried bool
+retry:
+	err := syscall.Flock(int(f.fh.Fd()), flag|syscall.LOCK_NB)
+
+	switch err {
+	case syscall.EWOULDBLOCK:
+		return false, nil
+	case nil:
+		*locked = true
+		return true, nil
+	}
+	if !retried {
+		if shouldRetry, reopenErr := f.reopenFDOnError(err); reopenErr != nil {
+			return false, reopenErr
+		} else if shouldRetry {
+			retried = true
+			goto retry
+		}
+	}
+
+	return false, err
+}
+
+// reopenFDOnError determines whether we should reopen the file handle
+// in readwrite mode and try again. This comes from util-linux/sys-utils/flock.c:
+//  Since Linux 3.4 (commit 55725513)
+//  Probably NFSv4 where flock() is emulated by fcntl().
+func (f *Flock) reopenFDOnError(err error) (bool, error) {
+	if err != syscall.EIO && err != syscall.EBADF {
+		return false, nil
+	}
+	if st, err := f.fh.Stat(); err == nil {
+		// if the file is able to be read and written
+		if st.Mode()&0600 == 0600 {
+			f.fh.Close()
+			f.fh = nil
+
+			// reopen in read-write mode and set the filehandle
+			fh, err := os.OpenFile(f.path, os.O_CREATE|os.O_RDWR, os.FileMode(0600))
+			if err != nil {
+				return false, err
+			}
+			f.fh = fh
+			return true, nil
+		}
+	}
+
+	return false, nil
+}