How to access /dev/ttyS* ?

Ryan Johnson ryan.johnson@cs.utoronto.ca
Thu Apr 26 23:58:00 GMT 2012


On 26/04/2012 4:04 PM, Corinna Vinschen wrote:
> On Apr 26 11:48, Ryan Johnson wrote:
>> Hi all,
>>
>> I'm trying to connect a VirtualBox guest's serial port to something
>> that cygwin/gdb can access for remote debugging, and am having
>> trouble connecting the pieces...
>>
>> One post from a couple of years ago [1] suggests using /dev/ttyS* to
>> access COM ports. This would work great... except there are no
>> /dev/ttyS* on my install.
> If the VM has a virtual HW serial port configured, you should see a
> /dev/ttyS0 entry.  If it's not there, you didn't configure it.  Cygwin
> in the guest can only access what is available in the guest OS.  If
> there's a COM1, Cygwin has a /dev/ttyS0.
Ah, I'm trying to debug a linux guest from cygwin/win7 host. I guess the 
problem is my laptop doesn't have a physical COM1 port, so there's no 
way to route anything to it (and nothing for cygwin to display in /dev).

>> The other VirtualBox option is to create a named pipe (as in Windows
>> NPFS), and then wrap it into a pty using socat [2], but I can't
>> figure out how to access such a pipe from cygwin -- the "\\.\pipe\*"
>> path doesn't seem to be supported by cygpath and there's nothing
>> obvious in /dev/.
> I don't know how that's supposed to work, but you could try to
> connect it via /proc/sys/Device/NamedPipe/<name-of-named-pipe>
> No guarantee that it works, though.
No love... I get "no such process." In retrospect I shouldn't have 
expected that to work, tho. Named pipes are undoubtedly very different 
beasts in Windows vs Posix.

It looks like my options are to run a second VM that points at the same 
named pipe and debug from within it, or use vmwaregateway [1] to convert 
it to TCP so my cygwin-based gdb can connect to it.  Both work.

[1] http://www.l4ka.org/91.php

Thanks anyway,
Ryan




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