You can't spell "evil" without "vi".
rob at landley.net
Mon Oct 13 04:48:22 UTC 2008
If you use the cursor keys in vi, it adds three characters at a time. (The
ansi "move cursor" sequence for the direction you hit.) If you hold it down
so it repeats, on a slow system (such as qemu's arm emulation) or one that's
heavily loaded, you can easily have several of them queue up before VI gets
A dozen times 3 characters is 36 characters. If you look at editors/vi.c line
216 you'll see that the buffer you're reading into (readbuffer) is 32
characters. I.E. your buffer is not divisible by 3, so it'll read an even 10
cursor lefts, plus an escape left bracket pair which isn't part of a
recognized sequence, so is interpreted as separate characters. The escape
drops you out of insert mode and into edit mode.
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
So basically, busybox vi is corrupting your data when you cursor around in a
file on a loaded system. Wheee...
P.S. And no, making the buffer bigger isn't necessarily going to fix it, you
need a flag that remembers the last buffer was full so when you check for
more data you treat it as part of the same unit for multi-character
P.P.S. An additional complication is that the readahead code (circa line 2270)
to check for more characters specifically for an escape sequence fills the
buffer up to sizeof()-8 (I.E. 24), which by pure luck is divisible by 3,
although not all sequences are. But in any case, I'm not quite sure what
this is doing. Seems overcomplicated, but then the whole "#define G.thingy
thingy" bit copied into each file pretty much claimed "overcomplicated",
planeted a flag in it, an started reciting a national anthem. Is there
something wrong with just using G.thingy when that's what you mean? As for
copying G.chars_to_parse into n in readit(), if we didn't declare it volatile
that's exactly the sort of thing the optimizer should do _for_ us, isn't it?
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