linux-kernel - RE: [PATCH v2] mei: Avoid the use of one-element arrays

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Date:   Wed, 22 Jul 2020 19:04:25 +0000
From:   "Winkler, Tomas" <tomas.winkler@...el.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] mei: Avoid the use of one-element arrays


> 
> Hi all,
> 
> Friendly ping: who can take this? :)
> 
> Thanks
> --
> Gustavo
> 
> On 7/14/20 16:45, Gustavo A. R. Silva wrote:
> > One-element arrays are being deprecated[1]. Replace the one-element
> > arrays with a simple value type u8 reserved, once this is just a
> > placeholder for alignment.
> >
> > Also, while there, use the preferred form for passing a size of a struct.
> > The alternative form where struct name is spelled out hurts
> > readability and introduces an opportunity for a bug when the variable
> > type is changed but the corresponding sizeof that is passed as argument is
> not.
> >
> > [1] https://github.com/KSPP/linux/issues/79
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> > ---
> > Changes in v2:
> >  - Use a more concise changelog text.
> >
> >  drivers/misc/mei/hbm.c | 4 ++--
> >  drivers/misc/mei/hw.h  | 6 +++---
> >  2 files changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/misc/mei/hbm.c b/drivers/misc/mei/hbm.c index
> > a44094cdbc36..f020d5594154 100644
> > --- a/drivers/misc/mei/hbm.c
> > +++ b/drivers/misc/mei/hbm.c
> > @@ -408,14 +408,14 @@ static int mei_hbm_add_cl_resp(struct mei_device
> > *dev, u8 addr, u8 status)  {
> >  	struct mei_msg_hdr mei_hdr;
> >  	struct hbm_add_client_response resp;
> > -	const size_t len = sizeof(struct hbm_add_client_response);
> > +	const size_t len = sizeof(resp);
> >  	int ret;
> >
> >  	dev_dbg(dev->dev, "adding client response\n");
> >
> >  	mei_hbm_hdr(&mei_hdr, len);
> >
> > -	memset(&resp, 0, sizeof(struct hbm_add_client_response));
> > +	memset(&resp, 0, len);
> >  	resp.hbm_cmd = MEI_HBM_ADD_CLIENT_RES_CMD;
> >  	resp.me_addr = addr;
> >  	resp.status  = status;

This should be probably in a different patch it's not related to the second part.

> > diff --git a/drivers/misc/mei/hw.h b/drivers/misc/mei/hw.h index
> > b1a8d5ec88b3..8c0297f0e7f3 100644
> > --- a/drivers/misc/mei/hw.h
> > +++ b/drivers/misc/mei/hw.h
I have second thoughts of this part as all reserved fields in this file are of form u8 reserved[X], 
so we will lose that uniformity with this change, you have to look at the file as whole
not just at the patch.  So I prefer we drop that part of the patch. 

> > @@ -346,13 +346,13 @@ struct hbm_add_client_request {
> >   * @hbm_cmd: bus message command header
> >   * @me_addr: address of the client in ME
> >   * @status: if HBMS_SUCCESS then the client can now accept connections.
> > - * @reserved: reserved
> > + * @reserved: reserved for alignment.
> >   */
> >  struct hbm_add_client_response {
> >  	u8 hbm_cmd;
> >  	u8 me_addr;
> >  	u8 status;
> > -	u8 reserved[1];
> > +	u8 reserved;
> >  } __packed;
> >
> >  /**
> > @@ -461,7 +461,7 @@ struct hbm_notification {
> >  	u8 hbm_cmd;
> >  	u8 me_addr;
> >  	u8 host_addr;
> > -	u8 reserved[1];
> > +	u8 reserved;
> >  } __packed;
> >
> >  /**
> >