Re: [PATCH] kvm tools: Sanitize output characters in serial console

[walimis <walimisdev@gmail.com>]

On Wed, Aug 10, 2011 at 02:15:45PM +0800, Asias He wrote:
>On 08/10/2011 01:55 PM, Pekka Enberg wrote:
>> On Wed, Aug 10, 2011 at 8:43 AM, Asias He <asias.hejun@gmail.com> wrote:
>>> On 08/10/2011 01:30 PM, Pekka Enberg wrote:
>>>> On 8/10/11 2:56 AM, Asias He wrote:
>>>>> This patch fixes strange characters in serial console.
>>>>>
>>>>> Before:
>>>>>
>>>>> [    0.448000] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
>>>>> �[    0.695000] serial8250: ttyS0 at I/O 0x3f8 (irq = 0) is a 16550A
>>>>> �[    0.942000] serial8250: ttyS1 at I/O 0x2f8 (irq = 0) is a 16550A
>>>>> �[    1.189000] serial8250: ttyS2 at I/O 0x3e8 (irq = 0) is a 16550A
>>>>> [    1.194000] Non-volatile memory driver v1.3
>>>>>
>>>>> After:
>>>>>
>>>>> [    0.541000] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
>>>>> [    0.788000] serial8250: ttyS0 at I/O 0x3f8 (irq = 0) is a 16550A
>>>>> [    1.041000] serial8250: ttyS1 at I/O 0x2f8 (irq = 0) is a 16550A
>>>>> [    1.294000] serial8250: ttyS2 at I/O 0x3e8 (irq = 0) is a 16550A
>>>>> [    1.309000] Non-volatile memory driver v1.3
>>>>>
>>>>> Signed-off-by: Asias He<asias.hejun@gmail.com>
>>>>> ---
>>>>>   tools/kvm/term.c |    7 +++++--
>>>>>   1 files changed, 5 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/tools/kvm/term.c b/tools/kvm/term.c
>>>>> index 2a3e1f0..85b41e7 100644
>>>>> --- a/tools/kvm/term.c
>>>>> +++ b/tools/kvm/term.c
>>>>> @@ -5,6 +5,7 @@
>>>>>   #include<unistd.h>
>>>>>   #include<sys/uio.h>
>>>>>   #include<signal.h>
>>>>> +#include<ctype.h>
>>>>>
>>>>>   #include "kvm/read-write.h"
>>>>>   #include "kvm/term.h"
>>>>> @@ -57,8 +58,10 @@ int term_putc(int who, char *addr, int cnt)
>>>>>       if (who != active_console)
>>>>>           return -1;
>>>>>
>>>>> -    while (cnt--)
>>>>> -        fprintf(stdout, "%c", *addr++);
>>>>> +    while (cnt--) {
>>>>> +        if (isascii(*addr))
>>>>
>>>> Do things like backspace still work with this?
>>>
>>> Sure. Have a try ;-)
>>>
>>> http://en.wikipedia.org/wiki/ASCII
>> 
>> OK, cool. Do we know what the extra characters are and why the guest
>> is sending them?
I think the reason is not important here. I use qemu to test
and it also outputs that extra characters. They seem to be outputted by
driver or kernel of guest os.

It's not sane to change the output of guest os. Suppose if we just 
want to see what "cat /dev/urandom" prints, then only 
allow ascii characters to be outputted? I think that's not what we expect.

walimis
>> 
>
>
>This tells us
>
>        while (cnt--) {
>               if (isascii(*addr))
>                       fprintf(stdout, "%c", *addr++);
>               else
>                       fprintf(stdout, "\n---%x---\n", *addr++);
>        }
>
>the extra chars is 0xff.
>
>The reason is not understood.
>
>-- 
>Best Regards,
>Asias He
>--
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