[SLOF] [PATCH] slof/fs/accept: Allow Unix LF line endings, too

Segher Boessenkool segher at kernel.crashing.org
Mon Aug 30 23:55:34 AEST 2021

On Mon, Aug 30, 2021 at 11:28:15PM +1000, Alexey Kardashevskiy wrote:
> On 30/08/2021 23:10, Segher Boessenkool wrote:
> >On Mon, Aug 30, 2021 at 12:53:08PM +0200, Thomas Huth wrote:
> >>Currently SLOF only accepts CR (0x0d) line endings at the command prompt,
> >>since this is the default line ending used on serial consoles.
> >
> >>However,
> >>sometimes people try to connect to SLOF directly in a way that uses the
> >>typical Unix LF line endings (0x0a) which are then completely ignored,
> >>for example running QEMU like this:
> >>
> >>  qemu-system-ppc64 -nodefaults \
> >>     -chardev socket,path=/tmp/mysocket,wait=off,id=cs0,server=on \
> >>     -device spapr-vty,id=serial0,reg=0x30000000,chardev=cs0
> >>
> >>and then connect to that Unix socket via "nc -U /tmp/mysocket".
> >>
> >>For such use cases, allow the 0x0a line ending in SLOF, too.
> >
> >How does that work if you feed text with CRLF combos?  If it does accept
> >a new line at both CR and LF, that is problematic (it violates both the
> >OF and ANS specifications of ACCEPT).
> Is it in of1275 somewhere? I looked but did not spot quickly.

Hrm, the text skirts the issues somewhat :-)  7.2, in any case.

1275 doesn't really say what to do with input from another source I

If you accept a new line at both CR and LF it will accept an empty line
after every "real" input line.  This breaks various things (and is super
annoying in the first place).

> >A "real" terminal sends CR only, by default, and can be switched to
> >send CRLF instead (by CSI 20h; switch back with CSI 20l).  You cannot do
> >only LF on a standard terminal.
> "strace cat" shows this on "enter":
> read(0, "\n", 131072)   = 1
> write(1, "\n", 1)       = 1
> What do I miss?

You didn't use a communications terminal.  You used a UNIX program :-)


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