Christian Schwarz
975fdee217
A bookmark with a well-known name is used to track which version was
last successfully received by the receiver.
The createtxg that can be retrieved from the bookmark using `zfs get` is
used to set the Replicated attribute of each snap on the sender:
If the snap's CreateTXG > the cursor's, it is not yet replicated,
otherwise it has been.
There is an optional config option to change the behvior to
`CreateTXG >= the cursor's`, and the implementation defaults to that.
The reason: While things work just fine with `CreateTXG > the cursor's`,
ZFS does not provide size estimates in a `zfs send` dry run
(see acd2418).
However, to enable the use case of keeping the snapshot only around for
the replication, the config flag exists.
59 lines
1.8 KiB
Go
59 lines
1.8 KiB
Go
package zfs
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import (
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"fmt"
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"github.com/pkg/errors"
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"strconv"
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)
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const ReplicationCursorBookmarkName = "zrepl_replication_cursor"
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// may return nil for both values, indicating there is no cursor
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func ZFSGetReplicationCursor(fs *DatasetPath) (*FilesystemVersion, error) {
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versions, err := ZFSListFilesystemVersions(fs, nil)
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if err != nil {
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return nil, err
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}
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for _, v := range versions {
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if v.Type == Bookmark && v.Name == ReplicationCursorBookmarkName {
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return &v, nil
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}
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}
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return nil, nil
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}
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func ZFSSetReplicationCursor(fs *DatasetPath, snapname string) (guid uint64, err error) {
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snapPath := fmt.Sprintf("%s@%s", fs.ToString(), snapname)
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propsSnap, err := zfsGet(snapPath, []string{"createtxg", "guid"})
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if err != nil {
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return 0, err
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}
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snapGuid, err := strconv.ParseUint(propsSnap.Get("guid"), 10, 64)
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bookmarkPath := fmt.Sprintf("%s#%s", fs.ToString(), ReplicationCursorBookmarkName)
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propsBookmark, err := zfsGet(bookmarkPath, []string{"createtxg"})
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_, bookmarkNotExistErr := err.(*DatasetDoesNotExist)
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if err != nil && !bookmarkNotExistErr {
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return 0, err
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}
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if err == nil {
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bookmarkTxg, err := strconv.ParseUint(propsBookmark.Get("createtxg"), 10, 64)
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if err != nil {
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return 0, errors.Wrap(err, "cannot parse bookmark createtxg")
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}
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snapTxg, err := strconv.ParseUint(propsSnap.Get("createtxg"), 10, 64)
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if err != nil {
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return 0, errors.Wrap(err, "cannot parse snapshot createtxg")
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}
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if snapTxg < bookmarkTxg {
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return 0, errors.New("replication cursor can only be advanced, not set back")
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}
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if err := ZFSDestroy(bookmarkPath); err != nil { // FIXME make safer by using new temporary bookmark, then rename, possible with channel programs
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return 0, err
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}
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}
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if err := ZFSBookmark(fs, snapname, ReplicationCursorBookmarkName); err != nil {
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return 0, err
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}
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return snapGuid, nil
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}
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