Re: canonicalize_filename_mode memory usage

[Eric Blake]

Sergey Poznyakoff <gray <at> gnu.org.ua> writes:

> A user of tar reported a suboptimal memory usage by the
> canonicalize_filename_mode.  Attached is the patch he
> proposed.  Any comments?

Who do we use as --author and/or reporter in the git commit?  The patch first 
appeared on the tar list in an email by Solar Designer, but it is not clear 
whether he wrote it, or whether we should attribute yet some other person.

>    *dest = '\0';
> 
> +  actual_size = strlen(rname) + 1;

Quite wasteful.  Rather than calling strlen and redoing an O(n) walk of the 
string, the actual length can be obtained via O(1) calculation using known 
values.

> +  if (rname_limit - rname > actual_size)
> +    rname = xrealloc (rname, actual_size);

For that matter, the temporary variable actual_size is not even needed.  I'd 
write the patch as just a 2-line addition:

if (rname_limit != dest + 1)
  rname = xrealloc (rname, dest - rname + 1);

But yes, it is probably a good idea to use the xrealloc to avoid the memory 
waste, since 4k is disproportionately larger than the typical canonical name, 
unless Jim has any other preferences as module owner.

-- 
Eric Blake