30.1.3.2 Basic Version Control with Locking

With a locking-based version control system (such as SCCS, and RCS in its default mode), C-x v v does the following:

• If there is more than one file in the VC fileset and the files have inconsistent version control statuses, signal an error. Also signal an error if the files in the fileset are missing (removed from the filesystem, but still tracked by version control).
• If each file in the VC fileset is not registered with a version control system, register the newly-added files in the fileset. See Registering a File for Version Control. If Emacs cannot find a system to register under, it prompts for a repository type, creates a new repository, and registers the VC fileset with it. You can also specify the system explicitly, see Advanced Control in C-x v v.
• If each file is registered and unlocked, check the files out: lock each one and make it writable, so that you can begin to edit it.
• If each file is locked by you and contains changes, commit (a.k.a. “check-in”) the changes. To do this, Emacs pops up a *vc-log* buffer; type the desired log entry for the new revision, followed by C-c C-c to commit (see Features of the Log Entry Buffer).
• If each file is locked by you, but you have not changed it, release the lock and make the file read-only again. This undoes previous check-out operation for files that were not changed since the checkout.
• If each file is locked by another user, ask whether you want to steal the lock. If you say yes, the file becomes locked by you, and a warning message is sent to the user who had formerly locked the file.
• If files in the fileset are unlocked, but have changes with respect to their last revision, offer to claim the lock for each such file or to revert the file to the last checked-in revision. (This situation is exceptional and should not normally happen.)

These rules also apply when you use CVS in locking mode, except that CVS does not support stealing locks.