How does Emacs find the buffer for a file?

[Kai Großjohann]

When you do C-x C-f /some/file RET, then Emacs runs
insert-file-contents and puts the output in some buffer.  How does
Emacs determine the buffer from the filename?

Here's some background on why I'm asking this strange question:

There is a bug in Tramp, and I don't know how to start tracking it
down.  Tramp allows you to edit remote files.  If you say C-x C-f
/foo RET (editing the local file /foo), and then say C-x C-f
/address@hidden/foo RET (editing a remote file, also named /foo, via
Tramp), then the remote file contents are inserted into the buffer
containing the local file /foo.

Evaling (buffer-file-name) and buffer-file-name in the remote file
returns "/[sm/address@hidden/foo".  (The "sm/" part is an optional part
of the Tramp filename syntax, and Tramp inserts a default value there
if it is not given by the user.)

kai
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