make sure temp file(s) are closed during defrag

[ghouscht]

Bug report criteria

• [X] This bug report is not security related, security issues should be disclosed privately via etcd maintainers.
• [X] This is not a support request or question, support requests or questions should be raised in the etcd discussion forums.
• [X] You have read the etcd bug reporting guidelines.
• [X] Existing open issues along with etcd frequently asked questions have been checked and this is not a duplicate.

What happened?

Some temp file(s) (https://github.com/etcd-io/etcd/blob/bd8896364a1d9adb554b538232004e5b2d6c850a/server/storage/backend/backend.go#L487) might not be closed during defrag. See discussion https://github.com/etcd-io/etcd/pull/18822#discussion_r1830692111 for more details.

[ghouscht]

/assign

Will take care of this.

[ghouscht]

Apparently if everything works as expected the temp file is closed:

• tmpdb.Close (*bbolt.DB) is called here: https://github.com/etcd-io/etcd/blob/7b70b5f6aebe5be44691b605d5b0d179c106cbc0/server/storage/backend/backend.go#L532 (which also closes the file descriptor of the db file)
• because of https://github.com/etcd-io/etcd/blob/7b70b5f6aebe5be44691b605d5b0d179c106cbc0/server/storage/backend/backend.go#L495-L497 the temporary file isn't opened again, so calling tmpdb.Close also closes the temp file descriptor

Probably in one of the error cases this doesn't happen. Need to check.

[ghouscht]

This is done. All PRs, including the ones for the backports to 3.4 and 3.5 have been merged.