Subject: Re: [PATCH net-next 4/4] tools: ynl: add --dbg-small-recv for easier kernel testing

From: Donald Hunter <[email-masked]>
Date: Mon, 04 Mar 2024 11:26:52 +0000

Jakub Kicinski <[email-masked]> writes:

> Most "production" netlink clients use large buffers to
> make dump efficient, which means that handling of dump
> continuation in the kernel is not very well tested.
>
> Add an option for debugging / testing handling of dumps.
> It enables printing of extra netlink-level debug and
> lowers the recv() buffer size in one go. When used
> without any argument (--dbg-small-recv) it picks
> a very small default (4000), explicit size can be set,
> too (--dbg-small-recv 5000).
>
> Example:
>
> $ ./cli.py [...] --dbg-small-recv
> Recv: read 3712 bytes, 29 messages
>    nl_len = 128 (112) nl_flags = 0x0 nl_type = 19
>  [...]
>    nl_len = 128 (112) nl_flags = 0x0 nl_type = 19
> Recv: read 3968 bytes, 31 messages
>    nl_len = 128 (112) nl_flags = 0x0 nl_type = 19
>  [...]
>    nl_len = 128 (112) nl_flags = 0x0 nl_type = 19
> Recv: read 532 bytes, 5 messages
>    nl_len = 128 (112) nl_flags = 0x0 nl_type = 19
>  [...]
>    nl_len = 128 (112) nl_flags = 0x0 nl_type = 19
>    nl_len = 20 (4) nl_flags = 0x2 nl_type = 3
>
> (the [...] are edits to shorten the commit message).
>
> Note that the first message of the dump is sized conservatively
> by the kernel.
>
> Signed-off-by: Jakub Kicinski <[email-masked]>
> ---
>  tools/net/ynl/cli.py | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/tools/net/ynl/cli.py b/tools/net/ynl/cli.py
> index 0f8239979670..e8a65fbc3698 100755
> --- a/tools/net/ynl/cli.py
> +++ b/tools/net/ynl/cli.py
> @@ -38,6 +38,8 @@ from lib import YnlFamily, Netlink
>                          const=Netlink.NLM_F_APPEND)
>      parser.add_argument('--process-unknown', action=argparse.BooleanOptionalAction)
>      parser.add_argument('--output-json', action='store_true')
> +    parser.add_argument('--dbg-small-recv', default=0, const=4000,
> +                        action='store', nargs='?', type=int)

This breaks ynl if you don't use '--dbg-small-recv', it passes 0 which
fails the _recv_size check.

>      args = parser.parse_args()
>  
>      def output(msg):
> @@ -53,7 +55,10 @@ from lib import YnlFamily, Netlink
>      if args.json_text:
>          attrs = json.loads(args.json_text)
>  
> -    ynl = YnlFamily(args.spec, args.schema, args.process_unknown)
> +    ynl = YnlFamily(args.spec, args.schema, args.process_unknown,
> +                    recv_size=args.dbg_small_recv)
> +    if args.dbg_small_recv:
> +        ynl.set_recv_dbg(True)
>  
>      if args.ntf:
>          ynl.ntf_subscribe(args.ntf)