netdev - Re: [PATCH iproute2] utils: bump max args number to 256 for batch files

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Date:   Wed, 9 Jun 2021 16:59:49 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Guillaume Nault <gnault@...hat.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH iproute2] utils: bump max args number to 256 for batch
 files

On Tue, 1 Jun 2021 19:09:31 +0200
Guillaume Nault <gnault@...hat.com> wrote:

> Large tc filters can have many arguments. For example the following
> filter matches the first 7 MPLS LSEs, pops all of them, then updates
> the Ethernet header and redirects the resulting packet to eth1.
> 
> filter add dev eth0 ingress handle 44 priority 100 \
>   protocol mpls_uc flower mpls                     \
>     lse depth 1 label 1040076 tc 4 bos 0 ttl 175   \
>     lse depth 2 label 89648 tc 2 bos 0 ttl 9       \
>     lse depth 3 label 63417 tc 5 bos 0 ttl 185     \
>     lse depth 4 label 593135 tc 5 bos 0 ttl 67     \
>     lse depth 5 label 857021 tc 0 bos 0 ttl 181    \
>     lse depth 6 label 239239 tc 1 bos 0 ttl 254    \
>     lse depth 7 label 30 tc 7 bos 1 ttl 237        \
>   action mpls pop protocol mpls_uc pipe            \
>   action mpls pop protocol mpls_uc pipe            \
>   action mpls pop protocol mpls_uc pipe            \
>   action mpls pop protocol mpls_uc pipe            \
>   action mpls pop protocol mpls_uc pipe            \
>   action mpls pop protocol mpls_uc pipe            \
>   action mpls pop protocol ipv6 pipe               \
>   action vlan pop_eth pipe                         \
>   action vlan push_eth                             \
>     dst_mac 00:00:5e:00:53:7e                      \
>     src_mac 00:00:5e:00:53:03 pipe                 \
>   action mirred egress redirect dev eth1
> 
> This filter has 149 arguments, so it can't be used with tc -batch
> which is limited to a 100.
> 
> Let's bump the limit to the next power of 2. That should leave a lot of
> room for big batch commands.
> 
> Signed-off-by: Guillaume Nault <gnault@...hat.com>

Good idea, but we should probably go further up to 512.
Also, rather than keeping magic constant. Why not add value to
utils.h.

I considered using sysconf(_SC_ARG_MAX) gut that is huge on modern
machines (2M). And we don't need to allocate for all possible args.

diff --git a/include/utils.h b/include/utils.h
index 187444d52b41..6c4c403fe6c2 100644
--- a/include/utils.h
+++ b/include/utils.h
@@ -50,6 +50,9 @@ void incomplete_command(void) __attribute__((noreturn));
 #define NEXT_ARG_FWD() do { argv++; argc--; } while(0)
 #define PREV_ARG() do { argv--; argc++; } while(0)
 
+/* upper limit for batch mode */
+#define MAX_ARGS 512
+
 #define TIME_UNITS_PER_SEC     1000000
 #define NSEC_PER_USEC 1000
 #define NSEC_PER_MSEC 1000000
diff --git a/lib/utils.c b/lib/utils.c
index 93ae0c55063a..0559923beced 100644
--- a/lib/utils.c
+++ b/lib/utils.c
@@ -1714,10 +1714,10 @@ int do_batch(const char *name, bool force,
 
        cmdlineno = 0;
        while (getcmdline(&line, &len, stdin) != -1) {
-               char *largv[100];
+               char *largv[MAX_ARGS];
                int largc;
 
-               largc = makeargs(line, largv, 100);
+               largc = makeargs(line, largv, MAX_ARGS);
                if (!largc)
                        continue;       /* blank line */