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

From: Guillaume Nault <[email-masked]>
Date: Thu, 10 Jun 2021 09:58:57 +0200

On Wed, Jun 09, 2021 at 04:59:49PM -0700, Stephen Hemminger wrote:
> On Tue, 1 Jun 2021 19:09:31 +0200
> Guillaume Nault <[email-masked]> 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 <[email-masked]>
> 
> Good idea, but we should probably go further up to 512.
> Also, rather than keeping magic constant. Why not add value to
> utils.h.

Yes, right.

> 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.

Yes, 2M is probably overkill (and too much to allocate on the stack).

> 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 */
>  
> 

Is this a patch you're going to apply, or should I repost it formally?