linux-kernel - Re: [KJ] kmalloc to kzalloc patches for drivers/block [sane version]

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Date:	Thu, 21 Sep 2006 22:40:10 -0700
From:	"Om Narasimhan" <om.turyx@...il.com>
To:	"Nishanth Aravamudan" <nacc@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, kernel-janitors@...ts.osdl.org
Subject: Re: [KJ] kmalloc to kzalloc patches for drivers/block [sane version]

Thanks for the comments.
> >
> > Signed off by Om Narasimhan <om.turyx@...il.com>
>
> This is not the canonical format, per SubmittingPatches. It should be:
>
> Signed-off-by: Random J Developer <random@...eloper.example.org>
OK. I would take care of it.
>
> >  drivers/block/cciss.c    |    4 +--
> >  drivers/block/cpqarray.c |   72 +++++++++++++++-------------------------------
> >  drivers/block/loop.c     |    4 +--
> >  3 files changed, 25 insertions(+), 55 deletions(-)
>
> Your diffstat should have indicated to you that this should be split up
> better. Please (re-)read SubmittingPatches. *One* logical change per
> patch, most importantly.
OK. I would resubmit.
> >
> > diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
> > index 2cd3391..a800a69 100644
> > --- a/drivers/block/cciss.c
> > +++ b/drivers/block/cciss.c
> > @@ -900,7 +900,7 @@ #if 0                             /* 'buf_size' member is 16-bits
> >                               return -EINVAL;
> >  #endif
> >                       if (iocommand.buf_size > 0) {
> > -                             buff = kmalloc(iocommand.buf_size, GFP_KERNEL);
> > +                             buff = kzalloc(iocommand.buf_size, GFP_KERNEL);
> >                               if (buff == NULL)
> >                                       return -EFAULT;
> >                       }
> > @@ -911,8 +911,6 @@ #endif
> >                                       kfree(buff);
> >                                       return -EFAULT;
> >                               }
> > -                     } else {
> > -                             memset(buff, 0, iocommand.buf_size);
> >                       }
> >                       if ((c = cmd_alloc(host, 0)) == NULL) {
> >                               kfree(buff);
>
> This changes performance potentially, no? The memset before was
> conditional upon (iocommand.Request.Type.Direction == XFER_WRITE) and
> now the memory will always be zero'd.
Yes, but not the functionality.
if (iocommand.buf_size > 0), code allocates using kmalloc. if
direction is XFER_WRITE, it does a copy_from_user(), and free()s the
allocated buffer, not really caring what data came in from userspace.
Else, it does memset(). So I could safely replace the kmalloc() with
kzalloc() without compromising functionality.

Thanks,
Om.
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