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/*
* Minio Cloud Storage, (C) 2016 Minio, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cmd
import (
"os"
pathutil "path"
"sync"
"github.com/minio/minio/pkg/lock"
)
// fsIOPool represents a protected list to keep track of all
// the concurrent readers at a given path.
type fsIOPool struct {
sync.Mutex
readersMap map[string]*lock.RLockedFile
}
// lookupToRead - looks up an fd from readers map and
// returns read locked fd for caller to read from, if
// fd found increments the reference count. If the fd
// is found to be closed then purges it from the
// readersMap and returns nil instead.
//
// NOTE: this function is not protected and it is callers
// responsibility to lock this call to be thread safe. For
// implementation ideas look at the usage inside Open() call.
func (fsi *fsIOPool) lookupToRead(path string) (*lock.RLockedFile, bool) {
rlkFile, ok := fsi.readersMap[path]
// File reference exists on map, validate if its
// really closed and we are safe to purge it.
if ok && rlkFile != nil {
// If the file is closed and not removed from map is a bug.
if rlkFile.IsClosed() {
// Log this as an error.
errorIf(errUnexpected, "Unexpected entry found on the map %s", path)
// Purge the cached lock path from map.
delete(fsi.readersMap, path)
// Indicate that we can populate the new fd.
ok = false
} else {
// Increment the lock ref, since the file is not closed yet
// and caller requested to read the file again.
rlkFile.IncLockRef()
}
}
return rlkFile, ok
}
// Open is a wrapper call to read locked file which
// returns a ReadAtCloser.
//
// ReaderAt is provided so that the fd is non seekable, since
// we are sharing fd's with concurrent threads, we don't want
// all readers to change offsets on each other during such
// concurrent operations. Using ReadAt allows us to read from
// any offsets.
//
// Closer is implemented to track total readers and to close
// only when there no more readers, the fd is purged if the lock
// count has reached zero.
func (fsi *fsIOPool) Open(path string) (*lock.RLockedFile, error) {
if err := checkPathLength(path); err != nil {
return nil, err
}
fsi.Lock()
rlkFile, ok := fsi.lookupToRead(path)
fsi.Unlock()
// Locked path reference doesn't exist, acquire a read lock again on the file.
if !ok {
// Open file for reading with read lock.
newRlkFile, err := lock.RLockedOpenFile(path)
if err != nil {
if os.IsNotExist(err) {
return nil, errFileNotFound
} else if os.IsPermission(err) {
return nil, errFileAccessDenied
} else if isSysErrIsDir(err) {
return nil, errIsNotRegular
} else if isSysErrNotDir(err) {
return nil, errFileAccessDenied
} else if isSysErrPathNotFound(err) {
return nil, errFileNotFound
}
return nil, err
}
/// Save new reader on the map.
// It is possible by this time due to concurrent
// i/o we might have another lock present. Lookup
// again to check for such a possibility. If no such
// file exists save the newly opened fd, if not
// reuse the existing fd and close the newly opened
// file
fsi.Lock()
rlkFile, ok = fsi.lookupToRead(path)
if ok {
// Close the new fd, since we already seem to have
// an active reference.
newRlkFile.Close()
} else {
// Save the new rlk file.
rlkFile = newRlkFile
}
// Save the new fd on the map.
fsi.readersMap[path] = rlkFile
fsi.Unlock()
}
// Success.
return rlkFile, nil
}
// Write - Attempt to lock the file if it exists,
// - if the file exists. Then we try to get a write lock this
// will block if we can't get a lock perhaps another write
// or read is in progress. Concurrent calls are protected
// by the global namspace lock within the same process.
func (fsi *fsIOPool) Write(path string) (wlk *lock.LockedFile, err error) {
if err = checkPathLength(path); err != nil {
return nil, err
}
wlk, err = lock.LockedOpenFile(path, os.O_RDWR, 0666)
if err != nil {
if os.IsNotExist(err) {
return nil, errFileNotFound
} else if os.IsPermission(err) {
return nil, errFileAccessDenied
} else if isSysErrIsDir(err) {
return nil, errIsNotRegular
}
return nil, err
}
return wlk, nil
}
// Create - creates a new write locked file instance.
// - if the file doesn't exist. We create the file and hold lock.
func (fsi *fsIOPool) Create(path string) (wlk *lock.LockedFile, err error) {
if err = checkPathLength(path); err != nil {
return nil, err
}
// Creates parent if missing.
if err = os.MkdirAll(pathutil.Dir(path), 0777); err != nil {
if os.IsPermission(err) {
return nil, errFileAccessDenied
} else if isSysErrNotDir(err) {
return nil, errFileAccessDenied
}
return nil, err
}
// Attempt to create the file.
wlk, err = lock.LockedOpenFile(path, os.O_RDWR|os.O_CREATE, 0666)
if err != nil {
if os.IsPermission(err) {
return nil, errFileAccessDenied
} else if isSysErrIsDir(err) {
return nil, errIsNotRegular
} else if isSysErrPathNotFound(err) {
return nil, errFileAccessDenied
}
return nil, err
}
// Success.
return wlk, nil
}
// Close implements closing the path referenced by the reader in such
// a way that it makes sure to remove entry from the map immediately
// if no active readers are present.
func (fsi *fsIOPool) Close(path string) error {
fsi.Lock()
defer fsi.Unlock()
if err := checkPathLength(path); err != nil {
return err
}
// Pop readers from path.
rlkFile, ok := fsi.readersMap[path]
if !ok {
return nil
}
// Close the reader.
rlkFile.Close()
// If the file is closed, remove it from the reader pool map.
if rlkFile.IsClosed() {
// Purge the cached lock path from map.
delete(fsi.readersMap, path)
}
// Success.
return nil
}