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store_previous.go
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/
store_previous.go
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// Copyright (c) 2016 Couchbase, 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 moss
import (
"fmt"
)
func (s *Store) snapshotPrevious(ss Snapshot) (Snapshot, error) {
footer, ok := ss.(*Footer)
if !ok {
return nil, fmt.Errorf("snapshot not a footer")
}
slocs, _ := footer.segmentLocs()
defer footer.DecRef()
if len(slocs) <= 0 {
return nil, nil
}
mref := slocs[0].mref
if mref == nil {
return nil, fmt.Errorf("footer mref nil")
}
mref.m.Lock()
if mref.refs <= 0 {
mref.m.Unlock()
return nil, fmt.Errorf("footer mmap has 0 refs")
}
fref := mref.fref
mref.m.Unlock() // Safe since the file beneath the mmap cannot change.
if fref == nil {
return nil, fmt.Errorf("footer fref nil")
}
fref.m.Lock()
if fref.refs <= 0 || fref.file == nil {
fref.m.Unlock()
return nil, fmt.Errorf("footer has 0 refs")
}
fref.m.Unlock() // Safe since the file ref count is positive.
finfo, err := fref.file.Stat()
if err != nil {
return nil, err
}
ssPrev, err := ScanFooter(s.options, fref, finfo.Name(), footer.PrevFooterOffset)
if err == ErrNoValidFooter {
return nil, nil
}
return ssPrev, err
}