linux-kernel - Re: [PATCH 13/13] libnvdimm, namespace: Publish page structure init state / control

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Message-ID: <CAPcyv4jHG9jCWz_hVc8DPxxALQ2JyD=AJKuYn6-ZMhB_fot1-Q@mail.gmail.com>
Date:   Thu, 5 Jul 2018 12:52:07 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Johannes Thumshirn <jthumshirn@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Jeff Moyer <jmoyer@...hat.com>, Christoph Hellwig <hch@....de>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 13/13] libnvdimm, namespace: Publish page structure init
 state / control

On Thu, Jul 5, 2018 at 12:49 PM, Matthew Wilcox <willy@...radead.org> wrote:
> On Thu, Jul 05, 2018 at 07:46:05AM -0700, Dan Williams wrote:
>> On Thu, Jul 5, 2018 at 1:29 AM, Johannes Thumshirn <jthumshirn@...e.de> wrote:
>> > On Wed, Jul 04, 2018 at 11:50:13PM -0700, Dan Williams wrote:
>> >> +static ssize_t memmap_state_store(struct device *dev,
>> >> +             struct device_attribute *attr, const char *buf, size_t len)
>> >> +{
>> >> +     int i;
>> >> +     struct nd_pfn *nd_pfn = to_nd_pfn_safe(dev);
>> >> +     struct memmap_async_state *async = &nd_pfn->async;
>> >> +
>> >> +     if (strcmp(buf, "sync") == 0)
>> >> +             /* pass */;
>> >> +     else if (strcmp(buf, "sync\n") == 0)
>> >> +             /* pass */;
>> >> +     else
>> >> +             return -EINVAL;
>> >
>> > Hmm what about:
>> >
>> >         if (strncmp(buf, "sync", 4))
>> >            return -EINVAL;
>> >
>> > This collapses 6 lines into 4.
>>
>> ...but that also allows 'echo "syncAndThenSomeGarbage" >
>> /sys/.../memmap_state' to succeed.
>
>         if (strncmp(buf, "sync", 4))
>                 return -EINVAL;
>         if (buf[4] != '\0' && buf[4] != '\n')
>                 return -EINVAL;
>

Not sure that's a win either, I'd rather just:

+       if (strcmp(buf, "sync") == 0 || strcmp(buf, "sync\n") == 0)
+               /* pass */;
+       else
+               return -EINVAL;

If we're trying to save those 2 lines.