You can't spell "evil" without "vi".

[Rob Landley]

On Sunday 12 October 2008 23:48:22 Rob Landley wrote:
> Next time it reads a buffer, it starts with the last character of a cursor
> left sequence: capital D.  Capital D is "delete to end of line", which it
> does.
>
> So basically, busybox vi is corrupting your data when you cursor around in
> a file on a loaded system.  Wheee...

Hmmm...  I redid the readit() code to only read ahead when processing an 
escape sequence.  (This let me shrink the readahead buffer to 8 bytes, 
actually 5 but with 32 bit alignment 8 makes more sense.  Bloatcheck says I 
shrunk the code by 17 bytes.)

Unfortunately, this mitigated the problem a bit, but didn't actually _fix_ it.  
It happens less often, but I can still trigger it.

I _think_ this is actually a qemu issue.  The escape sequences are being 
generated by the host Linux, which are then sent to the qemu process over a 
virtual serial console, which breaks them down into individual bytes with an 
interrupt for each.

This means that the blocking we're depending on to parse escape sequences 
doesn't work over a serial console.  You _can get an escape character by 
itself with poll saying there's no more data, and then on the next clock 
cycle you can get a "[D".

Hmmm...

Ok, making poll wait 300 miliseconds before deciding there's no next character 
in a pending escape sequence seems to have fixed it.  (At least I can't 
reproduce the problem under qemu anymore.)  The downside is that when you hit 
escape with nothing after it, the gui won't update for 1/3 of a second, but 
that's way better than corrupting data.

Rob