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

[Collin L. Walling]

On 10/20/2017 07:37 AM, Halil Pasic wrote:

On 10/20/2017 12:25 PM, Christian Borntraeger wrote:

From: "Collin L. Walling" <wall...@linux.vnet.ibm.com>

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

The check for buffer overflow was not there previously, or?

Maybe integrate that in the commit message too.

Good point.

Signed-off-by: Collin L. Walling <wall...@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com>
---
  pc-bios/s390-ccw/s390-ccw.h |  3 +++
  pc-bios/s390-ccw/sclp.c     | 17 ++++++++++++++---
  2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/pc-bios/s390-ccw/s390-ccw.h b/pc-bios/s390-ccw/s390-ccw.h
index 25d4d21..a8bd204 100644
--- a/pc-bios/s390-ccw/s390-ccw.h
+++ b/pc-bios/s390-ccw/s390-ccw.h
@@ -33,6 +33,9 @@ typedef unsigned long long __u64;
  #ifndef EBUSY
  #define EBUSY   2
  #endif
+#ifndef EFBIG
+#define EFBIG   3
+#endif
  #ifndef NULL
  #define NULL    0
  #endif
diff --git a/pc-bios/s390-ccw/sclp.c b/pc-bios/s390-ccw/sclp.c
index b1fc8ff..4795259 100644
--- a/pc-bios/s390-ccw/sclp.c
+++ b/pc-bios/s390-ccw/sclp.c
@@ -76,17 +76,28 @@ static int _strlen(const char *str)
  long write(int fd, const void *str, size_t len)
  {
      WriteEventData *sccb = (void *)_sccb;
+    const char *p;
+    size_t data_len = 0;

      if (fd != 1 && fd != 2) {
          return -EIO;
      }

-    sccb->h.length = sizeof(WriteEventData) + len;
+    for (p = str; *p; ++p) {
+        if (data_len > SCCB_DATA_LEN - 1) {
+            return -EFBIG;
+        }

We could also do a partial write or do more that one
sclp_service_call calls.

I don't think EFBIG is entirely correct here. From the man page:
"""
        EFBIG  An attempt was made to write a file that exceeds the implementa-
               tion-defined maximum file size or the process’s file size limit,
               or to write at a position past the maximum allowed offset.
"""

That's not what we have here IMHO.

From my perspective, the error code was a tie between EFBIG (consider
max sccb size as the maximum allowed offset) and ENOSPC:


"""
ENOSPC The device containing the file referred to by /fd/has no room
for the data.
"""


(consider "the file" as the sccb data buffer)

However, I extremely doubt we'll ever encounter an overflow from
printing during the bios (why would we print something that large?)
... perhaps the check is redundant?

+        if (*p == '\n') {
+            sccb->data[data_len++] = '\r';
+        }
+        sccb->data[data_len++] = *p;
+    }
+
+    sccb->h.length = sizeof(WriteEventData) + data_len;
      sccb->h.function_code = SCLP_FC_NORMAL_WRITE;
-    sccb->ebh.length = sizeof(EventBufferHeader) + len;
+    sccb->ebh.length = sizeof(EventBufferHeader) + data_len;
      sccb->ebh.type = SCLP_EVENT_ASCII_CONSOLE_DATA;
      sccb->ebh.flags = 0;
-    memcpy(sccb->data, str, len);

      sclp_service_call(SCLP_CMD_WRITE_EVENT_DATA, sccb);

Otherwise LGTM

Halil

--
- Collin L Walling