[libvirt] [PATCH] log: actually do substring matches with fnmatch

[Erik Skultety]

On Mon, May 14, 2018 at 02:53:49PM +0100, Daniel P. Berrangé wrote:
> Historically we matched log filters with strstr(), and when switching to
> fnmatch in cbb0fd3cfdc287f6f4653ef1f04a7cfb2ea51b27, it was stated that
> we would continue to match substrings, with "foo" being equivalent to
> "*foo*". Unfortuntely I forget to provide the code to actually make that
> happen. This fixes it to prepend and append "*" if not already present in
> the user's pattern.
>
> Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
> ---
>  src/util/virlog.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/src/util/virlog.c b/src/util/virlog.c
> index be9fc0cf78..d548010b10 100644
> --- a/src/util/virlog.c
> +++ b/src/util/virlog.c
> @@ -1409,6 +1409,8 @@ virLogFilterNew(const char *match,
>  {
>      virLogFilterPtr ret = NULL;
>      char *mdup = NULL;
> +    size_t mlen = strlen(match);
> +    size_t off = 0;
>
>      virCheckFlags(VIR_LOG_STACK_TRACE, NULL);
>
> @@ -1418,9 +1420,19 @@ virLogFilterNew(const char *match,
>          return NULL;
>      }
>
> -    if (VIR_STRDUP_QUIET(mdup, match) < 0)
> +    if (VIR_ALLOC_N_QUIET(mdup, mlen + 3) < 0)
>          return NULL;
>

At first glance it's not very clear why we need the hunk below, so I'd add a
comment stating that we treat a match 'foo' to be equal to '*foo*' for the
purposes of fnmatch() use.

Also, now that I see commit 8ccee910f5, I know we say
we treat the match always as substring, but I'd go even further and enhance the
sentence in that config (could be a separate patch) that not just 'foo', but
also '*foo' and 'foo*' are in fact equal to '*foo*' for that matter. But this
config change is not a deal-breaker to me.

> +    if (match[0] != '*') {
> +        mdup[off++] = '*';
> +    }

^Braces around a single line body...

> +    memcpy(mdup + off, match, mlen + 1);

Why do you copy the null byte too? 'mlen' should suffice.

> +    off += mlen;
> +    if (match[mlen - 1] != '*') {
> +        mdup[off++] = '*';
> +        mdup[off++] = '\0';

You won't need ^this extra null byte assignment, because we always use calloc
to allocate a block.

> +    }
> +
>      if (VIR_ALLOC_QUIET(ret) < 0) {
>          VIR_FREE(mdup);
>          return NULL;

With the nit-picks fixed and a commentary added right before the hunk this
patch adds:
Reviewed-by: Erik Skultety <eskultet at redhat.com>