[Devel] [PATCH VZ9 3/3] block/blk-cbt: add BLKCBTLIST ioctl

[Pavel Tikhomirov]

On 1/20/25 16:34, Andrey Zhadchenko wrote:
> so user can query the list of active bitmaps.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-96269
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
> ---
>   block/blk-cbt.c         | 38 ++++++++++++++++++++++++++++++++++++++
>   block/ioctl.c           |  1 +
>   include/uapi/linux/fs.h |  9 +++++++++
>   3 files changed, 48 insertions(+)
> 
> diff --git a/block/blk-cbt.c b/block/blk-cbt.c
> index 8b0d07ee757c..af242633acc9 100644
> --- a/block/blk-cbt.c
> +++ b/block/blk-cbt.c
> @@ -979,6 +979,42 @@ static int cbt_ioc_set(struct block_device *bdev, struct blk_user_cbt_info __use
>   	return ret;
>   }
>   
> +static int cbt_ioc_list(struct block_device *bdev, void __user *arg)
> +{
> +	void __user *name_ptr = (void *)((size_t)arg + sizeof(struct blk_user_cbt_list));
> +	struct request_queue *q = bdev_get_queue(bdev);
> +	struct blk_user_cbt_list lst;
> +	__u32 total = 0, copied = 0;
> +	struct cbt_info *cbt;
> +
> +	if (copy_from_user(&lst, arg, sizeof(lst)))
> +		return -EFAULT;
> +
> +	if (!access_ok(name_ptr,
> +		       lst.count * CBT_NAME_LENGTH))
> +		return -EFAULT;
> +
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(cbt, &q->cbt_list, list) {
> +		if (copied < lst.count) {
> +			if (copy_to_user(name_ptr, cbt->name, CBT_NAME_LENGTH))
> +				return -EFAULT;
> +			copied++;
> +			name_ptr = (void *)((size_t)name_ptr + CBT_NAME_LENGTH);
> +		}
> +		total++;
> +	}
> +	rcu_read_unlock();
> +
> +	lst.count = copied;
> +	lst.total_count = total;
> +
> +	if (copy_to_user(arg, &lst, sizeof(lst)))
> +		return -EFAULT;
> +
> +	return 0;
> +}
> +
>   static int cbt_ioc_misc(struct block_device *bdev, void __user *arg)
>   {
>   	struct request_queue *q = bdev_get_queue(bdev);
> @@ -1024,6 +1060,8 @@ int blk_cbt_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
>   		return cbt_ioc_set(bdev, ucbt_ioc, 0);
>   	case BLKCBTMISC:
>   		return cbt_ioc_misc(bdev, arg);
> +	case BLKCBTLIST:
> +		return cbt_ioc_list(bdev, arg);
>   	default:
>   		BUG();
>   	}
> diff --git a/block/ioctl.c b/block/ioctl.c
> index b2d3dbe5bef5..6e76d55790ea 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -569,6 +569,7 @@ static int blkdev_common_ioctl(struct block_device *bdev, blk_mode_t mode,
>   	case BLKCBTSET:
>   	case BLKCBTCLR:
>   	case BLKCBTMISC:
> +	case BLKCBTLIST:
>   		return blk_cbt_ioctl(bdev, cmd, (char __user *)arg);
>   	default:
>   		return -ENOIOCTLCMD;
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 667157fe864a..d4641a8a70a7 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -169,12 +169,21 @@ struct blk_user_cbt_snap_create {
>   	__u64 size;
>   };
>   
> +struct blk_user_cbt_list {
> +	__u32 count;		/* Amount of name entries in names
> +				 * in - available, out - filled
> +				 */
> +	__u32 total_count;	/* Total bitmap count of this device (out) */

Why do we need to know how many cbts were filled? It would always be 
min(available, total). So it seems we can use just one "count" variable 
with the same effect.

Also it might be a good idea to consider actual name lengths, so that 
buffer size can be decreased, to save (CBT_NAME_LENGTH - strlen(name) - 
1) memory for each name (e.g. separating names with spaces).

Another idea is to make this ioctl iterative, remembering position, so 
that we can read the list one by one using relatively small buffer.

> +	__u8 names[0];		/* Array of CBT_NAME_LENGTH long names */
> +};
> +
>   #define BLKCBTSTART _IOR(0x12,200, struct blk_user_cbt_info)
>   #define BLKCBTSTOP _IOR(0x12, 201, struct blk_user_cbt_info)
>   #define BLKCBTGET _IOWR(0x12,202,struct blk_user_cbt_info)
>   #define BLKCBTSET _IOR(0x12,203,struct blk_user_cbt_info)
>   #define BLKCBTCLR _IOR(0x12,204,struct blk_user_cbt_info)
>   #define BLKCBTMISC _IOWR(0x12,205,struct blk_user_cbt_misc_info)
> +#define BLKCBTLIST _IOWR(0x12, 206, struct blk_user_cbt_list)
>   
>   /*
>    * Flags for the fsx_xflags field

-- 
Best regards, Tikhomirov Pavel
Senior Software Developer, Virtuozzo.