Re: [Qemu-devel] [PATCH v2] s390-ccw: print carriage return with new lines

["Collin L. Walling" <walling@linux.vnet.ibm.com>]

On 10/26/2017 04:48 PM, Alexander Graf wrote:
>
> On 26.10.17 22:37, Collin L. Walling wrote:
>> On 10/26/2017 04:25 PM, Alexander Graf wrote:
>>> On 26.10.17 20:52, Collin L. Walling wrote:
>>>> The sclp console in the s390 bios writes raw data,
>>>> leading console emulators (such as virsh console) to
>>>> treat a new line ('\n') as just a new line instead
>>>> of as a Unix line feed. Because of this, output
>>>> appears in a "stair case" pattern.
>>>>
>>>> Let's print \r\n on every occurrence of a new line
>>>> in the string passed to write to amend this issue.
>>>>
>>>> This is in sync with the guest Linux code in
>>>> drivers/s390/char/sclp_vt220.c which also does a line feed
>>>> conversion  in the console part of the driver.
>>>>
>>>> This fixes the s390-ccw and s390-netboot output like
>>>> $ virsh start test --console
>>>> Domain test started
>>>> Connected to domain test
>>>> Escape character is ^]
>>>> Network boot starting...
>>>>                             Using MAC address: 02:01:02:03:04:05
>>>>                                                                  
>>>> Requesting information via DHCP:  010
>>>>
>>>> Signed-off-by: Collin L. Walling <walling@linux.vnet.ibm.com>
>>>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>>>> ---
>>>>    pc-bios/s390-ccw/sclp.c | 16 +++++++++++++---
>>>>    1 file changed, 13 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/pc-bios/s390-ccw/sclp.c b/pc-bios/s390-ccw/sclp.c
>>>> index 486fce1..f8ad5ae 100644
>>>> --- a/pc-bios/s390-ccw/sclp.c
>>>> +++ b/pc-bios/s390-ccw/sclp.c
>>>> @@ -68,17 +68,27 @@ void sclp_setup(void)
>>>>    long write(int fd, const void *str, size_t len)
>>>>    {
>>>>        WriteEventData *sccb = (void *)_sccb;
>>>> +    const char *p = str;
>>>> +    size_t data_len = 0;
>>>> +    size_t i;
>>>>          if (fd != 1 && fd != 2) {
>>>>            return -EIO;
>>>>        }
>>>>    -    sccb->h.length = sizeof(WriteEventData) + len;
>>>> +    for (i = len; i > 0; i--) {
>>> Where did the bounds check go? If you write(max) before, you were
>>> writing max bytes. If you do it now, you end up writing max + n bytes
>>> and potentially overflow the array, no?
>>>
>>>
>>> Alex
>> I wasn't a fan of the code aesthetics and being that the SCCB write buffer
>> allows about 4k bytes of data to be written to it, I felt it was safe to
>> remove it.  It's unlikely we'd be writing that much data in the bios, plus
>> that check did not exist prior to this fixup.
>>
>> Though, reading that out loud, it probably isn't the best idea to sacrifice
>> code robustness for code aesthetics.
>>
>> for (i = len; i > 0; i--) {
>>      if (data_len > SCCB_DATA_LEN - 1) {
>>          return -SOME_ERROR
>>      }
>>      if (*p == '\n') {
>>          sccb->data[data_len++] = '\r';
>>      }
>>      sccb->data[data_len++] = *p;
>>      p++;
>> }
>>
>> What do you think?
> Normally write() would just write less bytes than it was requested to
> write and tell you that in the return value. So how about
>
> for (i = 0; i < len; i++) {
>      if ((data_len + 1) >= SCCB_DATA_LEN) {
>          /* We would overflow the sccb buffer, abort early */
>          len = i;
>          break;
>      }
>
>      if (*p == '\n') {
>          /* Terminal emulators might need \r\n, so generate it */
>          sccb->data[data_len++] = '\r';
>      }
>
>      sccb->data[data_len++] = *p;
>      p++;
> }
>
>
> Alex
>
Makes sense to me.  I'll let this patch sit on the list for a little
while longer before fixing up for v3 in case Imight have missed
something else :)

Thanks for your time, Alex.

-- 
- Collin L Walling