[BUG] vi does not recognize changed permissions on read only files

[Cathey, Jim]

>This is wrong. Normally you keep the file descriptor open, then
>rewind/seek to the beginning of the file and write the new content.
>That way the system overhead for file reopen is avoided.

Normally, in an editor, you do NOT do this.  Consider what happens
if, behind the scenes, somebody did an "rm file".  Your hours of
typing would go into a still-open file, to an anonymous inode, and
then quietly disappear.

People's mental model of an editor is that it's editing a private
copy of the file, and only at open/save times does it refer to the
filesystem, and it will react to changes found therein.

File reopen time is TRIVIAL when compared to the thinking/typing cycle.

Consider the normal vi case when the file was (mistakenly) open RO:

ed rofile
<type type type>
:wq
<error>
:!chmod +w rofile
:wq
<OK>

This would not work if you'd held the FD open all that time.

-- Jim