Re: [PATCH] btrfs: join DEV_STATS ioctls to one

[Stefan Behrens <sbehrens@giantdisaster.de>]

On Fri, 22 Jun 2012 14:30:39 +0200, David Sterba wrote:
> Hi Chris,
> 
> please consider this patch for 3.5-rc before it goes final. Thanks.
> 
> From: David Sterba <dsterba@suse.cz>
> 
> Commit c11d2c236cc260b36 (Btrfs: add ioctl to get and reset the device
> stats) introduced two ioctls doing almost the same thing distinguished
> by just the ioctl number which encodes "do reset after read". I have
> suggested
> 
> http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg16604.html
> 
> to implement it via the ioctl args. This hasn't happen, and I think we
> should use a more clean way to pass flags and should not waste ioctl
> numbers.
> 
> CC: Stefan Behrens <sbehrens@giantdisaster.de>
> Signed-off-by: David Sterba <dsterba@suse.cz>
> ---
>  fs/btrfs/ioctl.c   |   16 ++++++++--------
>  fs/btrfs/ioctl.h   |    6 ++++--
>  fs/btrfs/volumes.c |    5 ++---
>  fs/btrfs/volumes.h |    3 +--
>  4 files changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 0e92e57..670c5d2 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3063,19 +3063,21 @@ static long btrfs_ioctl_scrub_progress(struct btrfs_root *root,
>  }
>  
>  static long btrfs_ioctl_get_dev_stats(struct btrfs_root *root,
> -				      void __user *arg, int reset_after_read)
> +				      void __user *arg)
>  {
>  	struct btrfs_ioctl_get_dev_stats *sa;
>  	int ret;
>  
> -	if (reset_after_read && !capable(CAP_SYS_ADMIN))
> -		return -EPERM;
> -
>  	sa = memdup_user(arg, sizeof(*sa));
>  	if (IS_ERR(sa))
>  		return PTR_ERR(sa);
>  
> -	ret = btrfs_get_dev_stats(root, sa, reset_after_read);
> +	if ((sa->flags & BTRFS_DEV_STATS_RESET) && !capable(CAP_SYS_ADMIN)) {
> +		kfree(sa);
> +		return -EPERM;
> +	}
> +
> +	ret = btrfs_get_dev_stats(root, sa);
>  
>  	if (copy_to_user(arg, sa, sizeof(*sa)))
>  		ret = -EFAULT;
> @@ -3473,9 +3475,7 @@ long btrfs_ioctl(struct file *file, unsigned int
>  	case BTRFS_IOC_BALANCE_PROGRESS:
>  		return btrfs_ioctl_balance_progress(root, argp);
>  	case BTRFS_IOC_GET_DEV_STATS:
> -		return btrfs_ioctl_get_dev_stats(root, argp, 0);
> -	case BTRFS_IOC_GET_AND_RESET_DEV_STATS:
> -		return btrfs_ioctl_get_dev_stats(root, argp, 1);
> +		return btrfs_ioctl_get_dev_stats(root, argp);
>  	}
>  
>  	return -ENOTTY;
> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
> index 497c530..c4089c5 100644
> --- a/fs/btrfs/ioctl.h
> +++ b/fs/btrfs/ioctl.h
> @@ -285,9 +285,13 @@ enum btrfs_dev_stat_values {
>  	BTRFS_DEV_STAT_VALUES_MAX
>  };
>  
> +/* Reset statistics after reading; needs SYS_ADMIN capability */
> +#define	BTRFS_DEV_STATS_RESET		(1ULL << 0)
> +
>  struct btrfs_ioctl_get_dev_stats {
>  	__u64 devid;				/* in */
>  	__u64 nr_items;				/* in/out */
> +	__u64 flags;				/* in/out */
>  
>  	/* out values: */
>  	__u64 values[BTRFS_DEV_STAT_VALUES_MAX];
> @@ -361,7 +365,5 @@ struct btrfs_ioctl_get_dev_stats {
>  					struct btrfs_ioctl_ino_path_args)
>  #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
>  				      struct btrfs_ioctl_get_dev_stats)
> -#define BTRFS_IOC_GET_AND_RESET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 53, \
> -					struct btrfs_ioctl_get_dev_stats)
>  
>  #endif
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 8a3d259..661e6ca 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -4871,8 +4871,7 @@ static void btrfs_dev_stat_print_on_load(struct btrfs_device *dev)
>  }
>  
>  int btrfs_get_dev_stats(struct btrfs_root *root,
> -			struct btrfs_ioctl_get_dev_stats *stats,
> -			int reset_after_read)
> +			struct btrfs_ioctl_get_dev_stats *stats)
>  {
>  	struct btrfs_device *dev;
>  	struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
> @@ -4890,7 +4889,7 @@ int btrfs_get_dev_stats(struct btrfs_root *root,
>  		printk(KERN_WARNING
>  		       "btrfs: get dev_stats failed, not yet valid\n");
>  		return -ENODEV;
> -	} else if (reset_after_read) {
> +	} else if (stats->flags & BTRFS_DEV_STATS_RESET) {
>  		for (i = 0; i < BTRFS_DEV_STAT_VALUES_MAX; i++) {
>  			if (stats->nr_items > i)
>  				stats->values[i] =
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index 74366f2..e673589 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -292,8 +292,7 @@ struct btrfs_device *btrfs_find_device_for_logical(struct btrfs_root *root,
>  void btrfs_dev_stat_print_on_error(struct btrfs_device *device);
>  void btrfs_dev_stat_inc_and_print(struct btrfs_device *dev, int index);
>  int btrfs_get_dev_stats(struct btrfs_root *root,
> -			struct btrfs_ioctl_get_dev_stats *stats,
> -			int reset_after_read);
> +			struct btrfs_ioctl_get_dev_stats *stats);
>  int btrfs_init_dev_stats(struct btrfs_fs_info *fs_info);
>  int btrfs_run_dev_stats(struct btrfs_trans_handle *trans,
>  			struct btrfs_fs_info *fs_info);
> 

I still do not understand your reason and the benefit of your change.
The reset command and the read command are two completely different
operations. Therefore I assigned two different ioctl commands. Then you
can use strace to see which command is sent, and you can also grep the
sources without additional effort.