RFR: 8262491: AArch64: CPU description should contain compatible board list [v6]

[Yasumasa Suenaga]

On Thu, 11 Mar 2021 10:08:33 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> I updated PR, but it is different from your suggestion a bit. This version would return empty string when `open()` or `read()` returns error, and also `close()` would be called when `open()` succeeded.
>> 
>> Did you say we can call `read()` and `close()` even if `open()` failed? According to manpage, it seems to work (just return EBADF), but I feel strange a bit. If it is ok, I will do so.
>
> No, if `open()` fails we should return straight away, with an empty string. That needs an addition.
> We must, however, terminate the string with 0 at the correct point, at the end of the bytes read. Otherwise ` strlen() `reads uninitialized memory. If the `read()` fails, we must return an empty string.

I think my latest commit includes your suggestion:

* returns empty string ( `\0` ) when `open()` failed.
* returns empty string when `read()` failed or read nothing (returns `0` )
* add `\0` to `buf[read_sz]` just after `read()` call, and skip it at the loop - it can be assumed `\0` is set to tail of `buf`

Or should I change as following for readability?

int fd = open("/proc/device-tree/compatible", O_RDONLY);
if (fd == -1) {
  *buf = '\0';
  return;
}

ssize_t read_sz = read(fd, buf, buflen - 1);
if (read_sz <= 0) {
  *buf = '\0';
  return;
}

// Add '\0' to the tail
buf[read_sz] = '\0';
// Replace '\0' to ' '
for (char *ch = buf; ch < buf + read_sz; ch++) {
  if (*ch == '\0') {
    *ch = ' ';
  }
}

close(fd);

-------------

PR: https://git.openjdk.java.net/jdk/pull/2759