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From Jim Jagielski <...@jaguNET.com>
Subject shared mem and apr_file_seek
Date Sat, 25 Jan 2014 17:37:18 GMT
As can be seen, I'm trying to do some work on shm; in
case we keep using ftok(...,1) for SysV, I want to make
posix shm a viable alternative, but I'm running into
some issues.

One semi-immediate on is that we do the following:

    tmpfd = shm_open(shm_name, O_RDWR | O_CREAT | O_EXCL, 0644);
       ...
    status = apr_os_file_put(&file, &tmpfd,
       ...
    status = apr_file_trunc(file, new_m->realsize);

And the apr_file_trunc fails for me with an Illegal
seek. In apr_file_trunc we do:

    if (ftruncate(fp->filedes, offset) == -1) {
        return errno;
    }
    return apr_file_seek(fp, APR_SET, &offset);

and apr_file_seek() does a lseek(). And that's where
the problem is because lseek() returns -1 with ESPIPE.

That seems like a valid error in this case, which begs
the following questions:

  1. Why are we doing the apr_file_trunc() in shm?
  2. Assuming it's required, why do we expect the lseek
     on it to succeed?
  3. Assuming the failure is NOT expected, or is system
     dependent, how should apr_file_seek handle it?



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