linux-kernel - Re: [PATCH] RDMA: usnic: Fix misuse of sysfs_emit

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Date:   Fri, 15 Jan 2021 16:21:40 -0800
From:   Joe Perches <joe@...ches.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        Christian Benvenuti <benve@...co.com>,
        Nelson Escobar <neescoba@...co.com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-rdma@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Greg KH <greg@...ah.com>
Subject: Re: [PATCH] RDMA: usnic: Fix misuse of sysfs_emit_at

On Fri, 2021-01-15 at 14:15 -0800, James Bottomley wrote:
> On Fri, 2021-01-15 at 13:23 -0800, Joe Perches wrote:
> > In commit e28bf1f03b01 ("RDMA: Convert various random sprintf sysfs
> > _show
> > uses to sysfs_emit") I mistakenly used len = sysfs_emit_at to
> > overwrite
> > the last trailing space of potentially multiple entry output.
> > 
> > The length of the last sysfs_emit_at call is 1 and it should instead
> > be
> > ignored.  Do so.
> > 
> > Fixes: e28bf1f03b01 ("RDMA: Convert various random sprintf sysfs
> > _show uses to sysfs_emit")
> > 
> > Reported-by: James Bottomley <James.Bottomley@...senPartnership.com>
> > Signed-off-by: Joe Perches <joe@...ches.com>
> > ---
> >  drivers/infiniband/hw/usnic/usnic_ib_sysfs.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/infiniband/hw/usnic/usnic_ib_sysfs.c
> > b/drivers/infiniband/hw/usnic/usnic_ib_sysfs.c
> > index e59615a4c9d9..fc077855b46c 100644
> > --- a/drivers/infiniband/hw/usnic/usnic_ib_sysfs.c
> > +++ b/drivers/infiniband/hw/usnic/usnic_ib_sysfs.c
> > @@ -231,7 +231,7 @@ static ssize_t summary_show(struct
> > usnic_ib_qp_grp *qp_grp, char *buf)
> >  		}
> >  	}
> >  
> > 
> > -	len = sysfs_emit_at(buf, len, "\n");
> > +	sysfs_emit_at(buf, len, "\n");	/* Overwrite the last
> > trailing space */
> 
> len is the offset of where the next character gets written, isn't it?
> so if you're overwriting the last character emitted into buf, shouldn't
> the offset point at that character rather than one beyond it?  So
> 
> sysfs_emit_at(buf, len - 1, "\n");	/* Overwrite the last trailing
> space */

<sigh> quite right, thanks for catching yet another braino from me today.

I'll step away from the keyboard and go back to doing other things today
after submitting a V2 with a more typical style without the silly
backspace/newline by trimming the trailing space from the formats...