malformed serial data being sent from guest

[Patto]

When sending data through serial from guest each time 0x0A byte is sent 0x0D is sent before it. For example, when sending {0x29, 0x0A} on the other end I receive {0x29, 0x0D, 0x0A}.

[Peter Maydell (pmaydell)]

Something somewhere in the stack is converting LF to CRLF. This could be something inside your guest, or in QEMU, or in the host; to find out where we need more detail.

Can you describe your setup, including:
 * complete QEMU command line
 * how you're sending data inside the guest
 * how you're reading it on the host end
please?

[Patto (pt300)]

I am unable to provide complete QEMU command line as I'm using virt-manager to deal with configuration. I can say that two serial ports are linked with physical ones through the /dev/ttyS* files.
The guests I tested it with are Windows 98 and Windows XP. For the testing I connected one port to another. I could confirm through a kernel level serial monitor that I was indeed sending just \n but on the second port I received \r\n. I also received \r\n when the port was read by the host.
Host is Ubuntu Xenial.

[Patto (pt300)]

After doing a bit of research I think line 142 in file chardev/char-serial.c is problematic. https://github.com/qemu/qemu/blob/master/chardev/char-serial.c#L142

It enables output processing, which is something unwanted here. With a simple test program I found out that by default, besides OPOST, ONLCR flag is set in c_oflag. I guess fix would be removing OPOST flag, which would disable any output processing, or setting c_oflag to 0 just to be sure.

[Patto (pt300)]

Seems like the problems isn't really new and might be at least 6 years old if not more. https://robert.penz.name/550/mapping-a-serial-device-to-a-kvm-guest-may-lead-to-communication-problems/

[Thomas Huth (th-huth)]

It's even older than 6 years, see:
https://lists.nongnu.org/archive/html/qemu-devel/2006-06/msg00196.html
and:
https://bugs.launchpad.net/qemu/+bug/1407813
https://bugs.launchpad.net/qemu/+bug/1715296

[Thomas Huth (th-huth)]

Patch has now been committed here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=12fb0ac0575df83cec72ec