linux-kernel - Re: [RFC v8 01/10] mm/damon/debugfs: Allow users to set initial monitoring target regions

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Message-ID: <20200901063542.1290-1-sjpark@amazon.com>
Date:   Tue, 1 Sep 2020 08:35:42 +0200
From:   SeongJae Park <sjpark@...zon.com>
To:     Marco Elver <elver@...gle.com>
CC:     SeongJae Park <sjpark@...zon.com>, <akpm@...ux-foundation.org>,
        "SeongJae Park" <sjpark@...zon.de>, <Jonathan.Cameron@...wei.com>,
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Subject: Re: [RFC v8 01/10] mm/damon/debugfs: Allow users to set initial monitoring target regions

On Mon, 31 Aug 2020 20:08:44 +0200 Marco Elver <elver@...gle.com> wrote:

> On Mon, Aug 31, 2020 at 12:47PM +0200, SeongJae Park wrote:
> [...]
> > diff --git a/mm/damon.c b/mm/damon.c
> > index 7e3c8c82a010..9815d22fc4de 100644
> > --- a/mm/damon.c
> > +++ b/mm/damon.c
> > @@ -2001,6 +2001,147 @@ static ssize_t debugfs_record_write(struct file *file,
> >  	return ret;
> >  }
> >  
> > +static ssize_t sprint_init_regions(struct damon_ctx *c, char *buf, ssize_t len)
> > +{
> > +	struct damon_target *t;
> > +	struct damon_region *r;
> > +	int written = 0;
> > +	int rc;
> > +
> > +	damon_for_each_target(t, c) {
> > +		damon_for_each_region(r, t) {
> > +			rc = snprintf(&buf[written], len - written,
> > +					"%lu %lu %lu\n",
> > +					t->id, r->ar.start, r->ar.end);
> 
> This most likely will not work as intended, because snprintf() returns
> "[...] the number of characters which would be generated for the given
> input, excluding the trailing null [...]". Would scnprintf() -- which
> returns "[...] the number of characters written into @buf not including
> the trailing '\0' [...]" -- do what you intended?

Ah, you're right!  I will use 'scnprintf' instead, not only here but in other
relevant parts.


Thanks,
SeongJae Park

> 
> > +			if (!rc)
> > +				return -ENOMEM;
> > +			written += rc;
> > +		}
> > +	}
> > +	return written;
> > +}
> [...]