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Date: Tue, 14 Jul 2020 13:08:55 -0500 From: "Gustavo A. R. Silva" <gustavoars@...nel.org> To: "Winkler, Tomas" <tomas.winkler@...el.com> Cc: Arnd Bergmann <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH][next] mei: Avoid the use of one-element arrays On Tue, Jul 14, 2020 at 05:54:32PM +0000, Winkler, Tomas wrote: > > > > There is a regular need in the kernel to provide a way to declare having a > > dynamically sized set of trailing elements in a structure. > > Kernel code should always use “flexible array members”[1] for these cases > > or, as in this particular case, replace the one-element array with a simple > > value type u8 reserved once this is just a placeholder for alignment. The older > > style of one-element or zero-length arrays should no longer be used[2]. > > > > 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://en.wikipedia.org/wiki/Flexible_array_member > > [2] https://github.com/KSPP/linux/issues/79 > > > > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org> > I'm okay with the patch but in this case the description is a bit off. > In this case there was no intention for a flexible arrays its just a reserved field. > The reserved field is actually mentioned in the description: "... or, as in this particular case, replace the one-element array with a simple value type u8 reserved once this is just a placeholder for alignment." Thanks -- Gustavo > > --- > > 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; > > 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 > > @@ -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; > > > > /** > > -- > > 2.27.0 >
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