[Qemu-devel] Abnormal function exit message in Qemu block drivers code

[shu ming <shuming@linux.vnet.ibm.com>]

Hi,
   After reading the block driver code in,  it was found that the error 
exit code behaved in different ways.  Here are some examples.  It seems 
that way 3 is a better way to log the error message.  In fact,  It is 
pretty important for a administrator to know what is going on and be 
informed the error when that happens. I believe  we should convert all 
the error exit code to way 3 gradually and make all the new code to 
follow an unique standard.
   Further more, really, some errors can be ignored while others can 
not.  So we can have a more flexible function to classify the level of 
the error message like
error_report(log_level,  "string format", string);

1)The error code exited silently.

case QCOW2_EXT_MAGIC_BACKING_FORMAT:
             if (ext.len >= sizeof(bs->backing_format)) {
                 fprintf(stderr, "ERROR: ext_backing_format: len=%u too 
large"
                         " (>=%zu)\n",
                         ext.len, sizeof(bs->backing_format));
                 return 2;
             }

2)  fprintf() to emit the error message

case QCOW2_EXT_MAGIC_BACKING_FORMAT:
             if (ext.len >= sizeof(bs->backing_format)) {
                 fprintf(stderr, "ERROR: ext_backing_format: len=%u too 
large"
                         " (>=%zu)\n",
                         ext.len, sizeof(bs->backing_format));
                 return 2;

3) A error_report() function to emit the error message.

/* Find driver and parse its options */
     drv = bdrv_find_format(fmt);
     if (!drv) {
         error_report("Unknown file format '%s'", fmt);
         ret = -EINVAL;
         goto out;
     }