[PATCH][next] misc: bcm-vk: Replace zero-length array with flexible array member

[PATCH][next] misc: bcm-vk: Replace zero-length array with flexible array member

[Gustavo A. R. Silva]

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. The older style of one-element or zero-length arrays should
no longer be used[2].

Also, make use of the struct_size() helper in kzalloc().

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/misc/bcm-vk/bcm_vk_msg.c | 3 +--
 drivers/misc/bcm-vk/bcm_vk_msg.h | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/bcm-vk/bcm_vk_msg.c b/drivers/misc/bcm-vk/bcm_vk_msg.c
index f40cf08a6192..6efc52b49af6 100644
--- a/drivers/misc/bcm-vk/bcm_vk_msg.c
+++ b/drivers/misc/bcm-vk/bcm_vk_msg.c
@@ -701,8 +701,7 @@ int bcm_vk_send_shutdown_msg(struct bcm_vk *vk, u32 shut_type,
 		return -EINVAL;
 	}
 
-	entry = kzalloc(sizeof(*entry) +
-			sizeof(struct vk_msg_blk), GFP_KERNEL);
+	entry = kzalloc(struct_size(entry, to_v_msg, 1), GFP_KERNEL);
 	if (!entry)
 		return -ENOMEM;
 
diff --git a/drivers/misc/bcm-vk/bcm_vk_msg.h b/drivers/misc/bcm-vk/bcm_vk_msg.h
index 4eaad84825d6..56784c8896d8 100644
--- a/drivers/misc/bcm-vk/bcm_vk_msg.h
+++ b/drivers/misc/bcm-vk/bcm_vk_msg.h
@@ -116,7 +116,7 @@ struct bcm_vk_wkent {
 	u32 usr_msg_id;
 	u32 to_v_blks;
 	u32 seq_num;
-	struct vk_msg_blk to_v_msg[0];
+	struct vk_msg_blk to_v_msg[];
 };
 
 /* queue stats counters */
-- 
2.27.0

Re: [PATCH][next] misc: bcm-vk: Replace zero-length array with flexible array member

[Scott Branden]

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Looks fine to me.

On 2021-05-14 4:08 p.m., Gustavo A. R. Silva 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. The older style of one-element or zero-length arrays should
> no longer be used[2].
> 
> Also, make use of the struct_size() helper in kzalloc().
> 
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Scott Branden <scott.branden@broadcom.com>
> ---
>  drivers/misc/bcm-vk/bcm_vk_msg.c | 3 +--
>  drivers/misc/bcm-vk/bcm_vk_msg.h | 2 +-
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/misc/bcm-vk/bcm_vk_msg.c b/drivers/misc/bcm-vk/bcm_vk_msg.c
> index f40cf08a6192..6efc52b49af6 100644
> --- a/drivers/misc/bcm-vk/bcm_vk_msg.c
> +++ b/drivers/misc/bcm-vk/bcm_vk_msg.c
> @@ -701,8 +701,7 @@ int bcm_vk_send_shutdown_msg(struct bcm_vk *vk, u32 shut_type,
>  		return -EINVAL;
>  	}
>  
> -	entry = kzalloc(sizeof(*entry) +
> -			sizeof(struct vk_msg_blk), GFP_KERNEL);
> +	entry = kzalloc(struct_size(entry, to_v_msg, 1), GFP_KERNEL);
>  	if (!entry)
>  		return -ENOMEM;
>  
> diff --git a/drivers/misc/bcm-vk/bcm_vk_msg.h b/drivers/misc/bcm-vk/bcm_vk_msg.h
> index 4eaad84825d6..56784c8896d8 100644
> --- a/drivers/misc/bcm-vk/bcm_vk_msg.h
> +++ b/drivers/misc/bcm-vk/bcm_vk_msg.h
> @@ -116,7 +116,7 @@ struct bcm_vk_wkent {
>  	u32 usr_msg_id;
>  	u32 to_v_blks;
>  	u32 seq_num;
> -	struct vk_msg_blk to_v_msg[0];
> +	struct vk_msg_blk to_v_msg[];
>  };
>  
>  /* queue stats counters */
> 


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