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Date: Tue, 10 Oct 2023 15:36:48 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Jiri Pirko <jiri@...nulli.us>
CC: <netdev@...r.kernel.org>, "David S . Miller" <davem@...emloft.net>, "Eric
Dumazet" <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
<pabeni@...hat.com>, Shannon Nelson <shannon.nelson@....com>, Michael Chan
<michael.chan@...adcom.com>, Edwin Peer <edwin.peer@...adcom.com>, "Cai
Huoqing" <cai.huoqing@...ux.dev>, George Cherian
<george.cherian@...vell.com>, Danielle Ratson <danieller@...dia.com>, "Moshe
Shemesh" <moshe@...dia.com>, Saeed Mahameed <saeedm@...dia.com>, Brett
Creeley <brett.creeley@....com>, Sunil Goutham <sgoutham@...vell.com>, Linu
Cherian <lcherian@...vell.com>, Geetha sowjanya <gakula@...vell.com>, Jerin
Jacob <jerinj@...vell.com>, hariprasad <hkelam@...vell.com>, Subbaraya
Sundeep <sbhatta@...vell.com>, Ido Schimmel <idosch@...dia.com>, Petr Machata
<petrm@...dia.com>, Eran Ben Elisha <eranbe@...dia.com>, Aya Levin
<ayal@...lanox.com>, Leon Romanovsky <leon@...nel.org>, Jesse Brandeburg
<jesse.brandeburg@...el.com>
Subject: Re: [PATCH net-next v1 1/8] devlink: retain error in struct
devlink_fmsg
On 10/10/23 13:34, Jiri Pirko wrote:
> Tue, Oct 10, 2023 at 12:43:11PM CEST, przemyslaw.kitszel@...el.com wrote:
>> Retain error value in struct devlink_fmsg, to relieve drivers from
>> checking it after each call.
>> Note that fmsg is an in-memory builder/buffer of formatted message,
>> so it's not the case that half baked message was sent somewhere.
>>
>> We could find following scheme in multiple drivers:
>> err = devlink_fmsg_obj_nest_start(fmsg);
>> if (err)
>> return err;
>> err = devlink_fmsg_string_pair_put(fmsg, "src", src);
>> if (err)
>> return err;
>> err = devlink_fmsg_something(fmsg, foo, bar);
>> if (err)
>> return err;
>> // and so on...
>> err = devlink_fmsg_obj_nest_end(fmsg);
>>
>> With retaining error API that translates to:
>> devlink_fmsg_obj_nest_start(fmsg);
>> devlink_fmsg_string_pair_put(fmsg, "src", src);
>> devlink_fmsg_something(fmsg, foo, bar);
>> // and so on...
>> err = devlink_fmsg_obj_nest_end(fmsg);
>
> I like this approach. But it looks a bit odd that you store error and
> return it as well, leaving the caller to decide what to do in his code.
> It is not desirable to leave the caller wondering.
>
> Also, it is customary to check the return value if the function returns
> it. This approach confuses the customs.
>
> Also, eventually, the fmsg is getting send. That is the point where the
> error could be checked and handled properly, for example by filling nice
> extack message.
>
> What I'm saying is, please convert them all to return void, store the
> error and check that before fmsg send. That makes the approach unified
> for all callers, code nicer. Even the custom in-driver put functions
> would return void. The callbacks (e. g. dump) would also return void.
I was also thinking about that,
what about cases that you want to exit early, say inside of some loop?
add also devlink_fmsg_is_err()?
anyway, I like results more with ultimate unification :), only then all
the drivers require conversion at the very same time
>
> + a small nit below:
>
>
>>
>> What means we check error just at the end
>> (one could return it directly of course).
>>
>> Possible error scenarios are developer error (API misuse) and memory
>> exhaustion, both cases are good candidates to choose readability
>> over fastest possible exit.
>>
>> This commit itself is an illustration of benefits for the dev-user,
>> more of it will be in separate commits of the series.
>>
>> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
>> Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
>> ---
>> add/remove: 2/4 grow/shrink: 11/9 up/down: 325/-646 (-321)
>> ---
>> net/devlink/health.c | 255 ++++++++++++++++---------------------------
>> 1 file changed, 92 insertions(+), 163 deletions(-)
>>
>> diff --git a/net/devlink/health.c b/net/devlink/health.c
>> index 638cad8d5c65..2d26479e9dbe 100644
>> --- a/net/devlink/health.c
>> +++ b/net/devlink/health.c
>> @@ -19,6 +19,7 @@ struct devlink_fmsg_item {
>>
>> struct devlink_fmsg {
>> struct list_head item_list;
>> + int err; /* first error encountered on some devlink_fmsg_XXX() call */
>> bool putting_binary; /* This flag forces enclosing of binary data
>> * in an array brackets. It forces using
>> * of designated API:
>> @@ -565,10 +566,8 @@ static int devlink_health_do_dump(struct devlink_health_reporter *reporter,
>> return 0;
>>
>> reporter->dump_fmsg = devlink_fmsg_alloc();
>> - if (!reporter->dump_fmsg) {
>> - err = -ENOMEM;
>> - return err;
>> - }
>> + if (!reporter->dump_fmsg)
>> + return -ENOMEM;
>>
>> err = devlink_fmsg_obj_nest_start(reporter->dump_fmsg);
>> if (err)
>> @@ -673,43 +672,59 @@ int devlink_nl_cmd_health_reporter_recover_doit(struct sk_buff *skb,
>> return devlink_health_reporter_recover(reporter, NULL, info->extack);
>> }
>>
>> -static int devlink_fmsg_nest_common(struct devlink_fmsg *fmsg,
>> - int attrtype)
>> +static bool _devlink_fmsg_err_or_binary(struct devlink_fmsg *fmsg)
>
> No need for "_" here. Drop it.
>
>
>> +{
>> + if (!fmsg->err && fmsg->putting_binary)
>> + fmsg->err = -EINVAL;
>> +
>> + return fmsg->err;
>> +}
>> +
>
> [...]
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