[fprint] GDM post-login messages box

[Eddie Hung]

Hello all,

I've looked into the slight problem of GDM displaying a dialog box
after you have successfully logged in, and I think I've worked out
why...

Basically, it's trying to show you any messages that *may* have
appeared *after* the main login window is destroyed, for example.

In it's current implementation, it doesn't know whether or not the
text box has been updated - but simply that it's not empty: and takes
no chances and displays a dialog box anyway.

pam_fprint doesn't say anything after a successful login, so we end up
seeing the same message as before. However, if I recall correctly,
pam_bioapi, on the other hand, does display a "login successful"
message after login, which you can see on the dialog.

The simple workaround would be to disable the dialog box altogether
(which can be quite easily done by commenting out one line).

A more complete solution would be to only display the dialog if
something was added to the box after a successful login.

Both these solutions involve altering GDM code - which would be rather
complicated - and also, GDM is currently undergoing a rewrite, so this
problem, and the proposals above, may or may not still apply. (I've
been unable to test the latest GDM for fear of breaking my only system
at the moment)

An alternative solution I have found is that the current GDM (2.20.2)
will clear the message buffer (rather than simply appending to it) if
an empty string is received - therefore if pam_fprint writes an empty
string after a successful login, then the buffer is cleared - and no
dialog appears.

The only side effect this creates is that you get an extra blank line
when using it at the console, e.g.

eddie at eddies-lappy ~ $ sudo -k
eddie at eddies-lappy ~ $ sudo echo hello
Scan right index finger on UPEK TouchStrip
upekts:error [read_msg] non-zero bytes in cmd response
upekts:error [read_msg28] expected response, got -1 seq=b4

hello
eddie at eddies-lappy ~ $

Hope this helps,

Eddie