MySQL Bugs: #26978: s->z_err not assigned a value?

Bug #26978	s->z_err not assigned a value?
Submitted:	9 Mar 2007 0:33	Modified:	9 Apr 2008 15:54
Reporter:	Chongfeng Hu	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Archive storage engine	Severity:	S3 (Non-critical)
Version:	5.1.17-BK, 5.2.0 falcon-alpha	OS:	Any (any)
Assigned to:	Sergey Vojtovich	CPU Architecture:	Any
Tags:	z_err

Description:
I found that whenever there's an error in processing, azio_stream->z_err should always contain an error number. However, in file storage/archive/azio.c, function int get_byte(s)  azio_stream *s;, I saw the following piece of code:

    if (s->stream.avail_in == 0)
    { 
      s->z_eof = 1;
      /* if (ferror(s->file)) s->z_err = Z_ERRNO; */
      return EOF;
    }

Here, the assignment to z_err is commented out. Should it still be assigned an appropriate value?

How to repeat:
I found this spot with the help of a code-analysis tool.

Thank you for a problem report. Verified by code review also on 5.1.17-BK. We have:

/* ===========================================================================
  Read a byte from a azio_stream; update next_in and avail_in. Return EOF
  for end of file.
  IN assertion: the stream s has been sucessfully opened for reading.
*/
int get_byte(s)
  azio_stream *s;
{
  if (s->z_eof) return EOF;
  if (s->stream.avail_in == 0)
  {
    errno = 0;
    s->stream.avail_in = my_read(s->file, (byte *)s->inbuf, AZ_BUFSIZE, MYF(0));
    if (s->stream.avail_in == 0)
    {
      s->z_eof = 1;
      /* if (ferror(s->file)) s->z_err = Z_ERRNO; */
      return EOF;
    }
    s->stream.next_in = s->inbuf;
  }
  s->stream.avail_in--;
  return *(s->stream.next_in)++;
}

So, even if it is not a bug (EOF may be just returned in case of any problem intentionally), this comment should be removed as misleading.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/39774

ChangeSet@1.2638, 2007-12-12 17:16:59+04:00, svoj@mysql.com +1 -0
  BUG#26978 - s->z_err not assigned a value?
  
  azio didn't handle situation when my_read() returns error.
  
  Added handling of situation when my_read() returns error.
  
  No test case for this fix.

Pushed into 5.1.24-rc

Pushed into 6.0.5-alpha

This is too low level change and it is very unlikely that somebody would experience this problem. Leaving the decision, whether to document this issue or not, to docs team with explanation below.

Memory corruption and/or server crash may occur when low-level I/O error occurs during opening an archive table.

Documented in the 5.1.24 and 6.0.5 changelogs as follows:

        Memory corruption, a crash of the MySQL server, or both, could take
        place if a low-level I/O error occurred while an ARCHIVE table was being
        opened.