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[204.195.96.226]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-70b4397c50csm4458126b3a.147.2024.07.10.16.11.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Jul 2024 16:11:40 -0700 (PDT) Date: Wed, 10 Jul 2024 16:11:39 -0700 From: Stephen Hemminger To: Maks Mishin , Guillaume Nault Cc: netdev@vger.kernel.org Subject: Re: [PATCH] f_flower: Remove always zero checks Message-ID: <20240710161139.578d20dc@hermes.local> In-Reply-To: <20240707172741.30618-1-maks.mishinFZ@gmail.com> References: <20240707172741.30618-1-maks.mishinFZ@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sun, 7 Jul 2024 20:27:41 +0300 Maks Mishin wrote: > Expression 'ttl & ~(255 >> 0)' is always zero, because right operand > has 8 trailing zero bits, which is greater or equal than the size > of the left operand == 8 bits. > > Found by RASU JSC. > > Signed-off-by: Maks Mishin > --- > tc/f_flower.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/tc/f_flower.c b/tc/f_flower.c > index 08c1001a..244f0f7e 100644 > --- a/tc/f_flower.c > +++ b/tc/f_flower.c > @@ -1523,7 +1523,7 @@ static int flower_parse_mpls_lse(int *argc_p, char ***argv_p, > > NEXT_ARG(); > ret = get_u8(&ttl, *argv, 10); > - if (ret < 0 || ttl & ~(MPLS_LS_TTL_MASK >> MPLS_LS_TTL_SHIFT)) { > + if (ret < 0) { > fprintf(stderr, "Illegal \"ttl\"\n"); > return -1; > } > @@ -1936,7 +1936,7 @@ static int flower_parse_opt(const struct filter_util *qu, char *handle, > } > mpls_format_old = true; > ret = get_u8(&ttl, *argv, 10); > - if (ret < 0 || ttl & ~(MPLS_LS_TTL_MASK >> MPLS_LS_TTL_SHIFT)) { > + if (ret < 0) { > fprintf(stderr, "Illegal \"mpls_ttl\"\n"); > return -1; > } That is correct mathematically, but perhaps the original author had different idea. Could we have review from someone familiar with MPLS support please.