linux-kernel - Re: [PATCH -next v2 2/9] blk-iocost: improve hanlder of match

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Message-ID: <Y4h9MEd3q4LXDGQq@slm.duckdns.org>
Date:   Thu, 1 Dec 2022 00:08:48 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     Li Nan <linan122@...wei.com>, josef@...icpanda.com,
        axboe@...nel.dk, cgroups@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next v2 2/9] blk-iocost: improve hanlder of match_u64()

On Thu, Dec 01, 2022 at 10:15:53AM +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2022/12/01 4:32, Tejun Heo 写道:
> > On Wed, Nov 30, 2022 at 09:21:49PM +0800, Li Nan wrote:
> > > From: Yu Kuai <yukuai3@...wei.com>
> > > 
> > > 1) There are one place that return value of match_u64() is not checked.
> > > 2) If match_u64() failed, return value is set to -EINVAL despite that
> > >     there are other possible errnos.
> > 
> > Ditto. Does this matter?
> > 
> 
> It's not a big deal, but I think at least return value of match_u64()
> should be checked, we don't want to continue with invalid input, right?

Yeah, sure.

> By the way, match_u64() can return -ERANGE, which can provide more
> specific error messge to user.

I'm really not convinced going over 64bit range would be all that difficult
to spot whether the error code is -EINVAL or -ERANGE. There isn't anything
wrong with returning -ERANGE but the fact that that particular function
returns an error code doesn't necessarily mean that it *must* be forwarded.

Imagine that we used sscanf(buf, "%llu", &value) to parse the number
instead. We'd only know whether the parsing would have succeeded or not and
would probably return -EINVAL on failure and the behavior would be just
fine. This does not matter *at all*.

So, idk, I'm not necessarily against it but changing -EINVAL to -ERANGE is
pure churn. Nothing material is being improved by that change.

Thanks.

-- 
tejun