On Fri, Jun 10, 2016 at 06:57:26PM +0700, Nguyễn Thái Ngọc Duy wrote:
> If the given string list has strdup_strings set (*), the string will be
> duplicated again. Pointless and leak memory. Ignore that flag.
>
> (*) only interpret-trailers.c does it at the moment
>
> Signed-off-by: Nguyễn Thái Ngọc Duy <[email protected]>
> ---
> parse-options-cb.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/parse-options-cb.c b/parse-options-cb.c
> index 239898d..8a1b6e6 100644
> --- a/parse-options-cb.c
> +++ b/parse-options-cb.c
> @@ -144,7 +144,7 @@ int parse_opt_string_list(const struct option *opt, const
> char *arg, int unset)
> if (!arg)
> return -1;
>
> - string_list_append(v, xstrdup(arg));
> + string_list_append_nodup(v, xstrdup(arg));
Hmm. So I agree this is an improvement, in the sense that we are
double-allocating when v->strdup_strings is set. But I think there's a
deeper issue here. Why are we always allocating in the first place?
If the memory we are getting in "arg" is not stable, then we _do_ need
to make a copy of it. But in that case, we want "strdup_strings" to be
set; without it any time we later run string_list_clear(), we leak the
allocated memory, because the struct has no idea that it is the owner of
the memory (and we do call string_list_clear() when we see "--no-foo").
If the memory _is_ stable, then we are fine to add a direct reference to
it, and can lose the extra xstrdup() here. Only the caller knows for
sure, so we should be respecting their value of strdup_strings (so lose
the xstrdup, but keep calling string_list_append()).
In practice, I suspect the memory _is_ stable, because we are generally
parsing command-line arguments. But it does not hurt to stay on the
conservative side, and always make a copy (in case we are parsing
something besides the global argv array) . Apparently I am the original
author of this code, in c8ba163 (parse-options: add OPT_STRING_LIST
helper, 2011-06-09), but there's no mention of this point there, in the
list archives, or in my brain.
So if we are doing the conservative thing, then I think the resulting
code should either look like:
if (!v->strdup_strings)
die("BUG: OPT_STRING_LIST should always use strdup_strings");
string_list_append(v, arg);
or:
/* silently enable for convenience */
v->strdup_strings = 1;
string_list_append(v, arg);
Of the two, I like the top one as it is less magical, but it would
require adjusting the initialization of the string-list for most of the
callers.
-Peff
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