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Date: Thu, 19 Oct 2023 23:49:29 +0200
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Simon Horman <horms@...nel.org>
CC: Jiri Pirko <jiri@...nulli.us>, <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>,
"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>,
Ariel Elior <aelior@...vell.com>,
Manish Chopra <manishc@...vell.com>,
Igor Russkikh <irusskikh@...vell.com>,
Coiby Xu <coiby.xu@...il.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>,
<linux-kernel@...r.kernel.org>,
Jesse Brandeburg <jesse.brandeburg@...el.com>,
Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next v3 01/11] devlink: retain error in struct
devlink_fmsg
On 10/19/23 15:00, Simon Horman wrote:
> On Wed, Oct 18, 2023 at 10:26:37PM +0200, Przemek Kitszel 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...
>> devlink_fmsg_obj_nest_end(fmsg);
>>
>> What means we check error just when is time to send.
>>
>> Possible error scenarios are developer error (API misuse) and memory
>> exhaustion, both cases are good candidates to choose readability
>> over fastest possible exit.
>>
>> Note that this patch keeps returning errors, to allow per-driver conversion
>> to the new API, but those are not needed at this point already.
>>
>> 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>
>> Reviewed-by: Jiri Pirko <jiri@...dia.com>
>> Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>
>
> ...
>
>> @@ -1027,14 +934,12 @@ int devlink_fmsg_binary_pair_put(struct devlink_fmsg *fmsg, const char *name,
>
> Hi Przemek,
>
> The line before this hunk is:
>
> err = devlink_fmsg_binary_put(fmsg, value + offset, data_size);
>
> And, as of this patch, the implementation of
> devlink_fmsg_binary_pair_nest_start() looks like this:
>
> int devlink_fmsg_binary_put(struct devlink_fmsg *fmsg, const void *value,
> u16 value_len)
> {
> if (!fmsg->putting_binary)
> return -EINVAL;
>
> return devlink_fmsg_put_value(fmsg, value, value_len, NLA_BINARY);
> }
>
> Which may return an error, if the if condition is met, without setting
> fmsg->err.
>
>> if (err)
>> break;
>> /* Exit from loop with a break (instead of
>> - * return) to make sure putting_binary is turned off in
>> - * devlink_fmsg_binary_pair_nest_end
>> + * return) to make sure putting_binary is turned off
>> */
>> }
>>
>> - end_err = devlink_fmsg_binary_pair_nest_end(fmsg);
>> - if (end_err)
>> - err = end_err;
>
> Prior to this patch, the value of err from the loop above was preserved,
> unless devlink_fmsg_binary_pair_nest_end generated an error.
>
>> + err = devlink_fmsg_binary_pair_nest_end(fmsg);
>
> But now it looks like this is only the case if fmsg->err corresponds to err
> when the loop was exited.
>
> Or in other words, the err returned by devlink_fmsg_binary_put()
> is not propagated to the caller if !fmsg->putting_binary.
>
> If so, is this intentional?
In scope of devlink_fmsg_binary_pair_put() all it's fine, and perhaps
that lead me into thinking that it's fine in *general*, which is not,
as devlink_fmsg_binary_put() is exported (so it's return value should
be preserved).
On the other note, it's called in two places (one of which was just
covered, and the second place is mlx5e_health_rsc_fmsg_binary(), which
really just mimics what we have here. So this is also fine in practice.
Last patch of the series fixes it for general case, so barring
pathological cherry-picks or reverts we are safe.
Do you want a v4 with that fixed?
Other thing is that this function could be changed into some internal
helper without export.
>
>> + fmsg->putting_binary = false;
>>
>> return err;
>> }
>> --
>> 2.38.1
>>
>
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