Re: [PATCH 1/5] btrfs: Make async snapshot ioctl more generic

[Goffredo Baroncelli <kreijack@libero.it>]

Hi Li,

great work, but I have some suggestions:

On Monday, 29 November, 2010, Li Zefan wrote:
> So we don't have to add new structures as we create more ioctls
> for snapshots.
> 
> Now to create async snapshot, set BTRFS_SNAPSHOT_CREATE_ASYNC bit of
> vol_arg_v2->flags, and then call ioctl(BTRFS_IOCT_SNAP_CREATE_V2).
> 
> Note: this changes the async snapshot ioctl ABI, which was merged
> in .37 merge window, so we have to make this change into .37.
> 
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
>  fs/btrfs/ioctl.c |   34 +++++++++++++++++++++-------------
>  fs/btrfs/ioctl.h |   12 ++++++++----
>  2 files changed, 29 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 463d91b..d3f1a60 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -935,23 +935,31 @@ out:
>  
>  static noinline int btrfs_ioctl_snap_create(struct file *file,
>  					    void __user *arg, int subvol,
> -					    int async)
> +					    bool v2)

This is a aesthetic suggestion: instead of passing a flag called v2 I suggest 
to add two wrapper functions, which extract the parameters and passes all 
available parameter to the "generic" function. Something like:

static inline btrfs_ioctl_snap_create_v1(struct file *file, 
						void __user *arg, int subvol)
{
                vol_args = memdup_user(arg, sizeof(*vol_args));
                if (IS_ERR(vol_args))
                        return PTR_ERR(vol_args);
                name = vol_args->name;
                fd = vol_args->fd;
                vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';

		btrfs_ioctl_snap_create_generic(file, subvol, name, fd, 0, 0);

}

static inline btrfs_ioctl_snap_create_v2(struct file *file, 
						void __user *arg, int subvol,
						)
{
                vol_args_v2 = memdup_user(arg, sizeof(*vol_args_v2));
                if (IS_ERR(vol_args_v2))
                        return PTR_ERR(vol_args_v2);

                ret = snap_check_flags(vol_args_v2->flags, true);
                if (ret)
                        goto out;

                name = vol_args_v2->name;
                fd = vol_args_v2->fd;
                vol_args_v2->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
                if (vol_args_v2->flags & BTRFS_SNAPSHOT_CREATE_ASYNC)
                        async = true;
                if (vol_args_v2->flags & BTRFS_SNAPSHOT_RDONLY)
                        readonly = true;

		btrfs_ioctl_snap_create_generic(file, subvol, name, fd, async,
			 readonly);

}

and 

  	case BTRFS_IOC_SNAP_CREATE:
  		return btrfs_ioctl_snap_create_v1(file, argp, 0);
	case BTRFS_IOC_SNAP_CREATE_V2:
  		return btrfs_ioctl_snap_create_v2(file, argp, 0);


Frankly speaking, we could get rid of the subvol parameter adding another 
wrapper function like "btrfs_ioctl_subvol_create( )", but this would be 
another story :)

>  {
>  	struct btrfs_ioctl_vol_args *vol_args = NULL;
> -	struct btrfs_ioctl_async_vol_args *async_vol_args = NULL;
> +	struct btrfs_ioctl_vol_args_v2 *vol_args_v2 = NULL;
>  	char *name;
>  	u64 fd;
>  	u64 transid = 0;
> +	bool async = false;
>  	int ret;
>  
> -	if (async) {
> -		async_vol_args = memdup_user(arg, sizeof(*async_vol_args));
> -		if (IS_ERR(async_vol_args))
> -			return PTR_ERR(async_vol_args);
> +	if (v2) {
> +		vol_args_v2 = memdup_user(arg, sizeof(*vol_args_v2));
> +		if (IS_ERR(vol_args_v2))
> +			return PTR_ERR(vol_args_v2);
>  
> -		name = async_vol_args->name;
> -		fd = async_vol_args->fd;
> -		async_vol_args->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
> +		if (vol_args_v2->flags & ~BTRFS_SNAPSHOT_CREATE_ASYNC) {
> +			ret = -EINVAL;
> +			goto out;
> +		}
> +
> +		name = vol_args_v2->name;
> +		fd = vol_args_v2->fd;
> +		vol_args_v2->name[BTRFS_SNAPSHOT_NAME_MAX] = '\0';
> +		if (vol_args_v2->flags & BTRFS_SNAPSHOT_CREATE_ASYNC)
> +			async = true;
>  	} else {
>  		vol_args = memdup_user(arg, sizeof(*vol_args));
>  		if (IS_ERR(vol_args))
> @@ -966,13 +974,13 @@ static noinline int btrfs_ioctl_snap_create(struct 
file *file,
>  
>  	if (!ret && async) {
>  		if (copy_to_user(arg +
> -				offsetof(struct btrfs_ioctl_async_vol_args,
> +				offsetof(struct btrfs_ioctl_vol_args_v2,
>  				transid), &transid, sizeof(transid)))
>  			return -EFAULT;
>  	}
> -
> +out:
>  	kfree(vol_args);
> -	kfree(async_vol_args);
> +	kfree(vol_args_v2);
>  
>  	return ret;
>  }
> @@ -2235,7 +2243,7 @@ long btrfs_ioctl(struct file *file, unsigned int
>  		return btrfs_ioctl_getversion(file, argp);
>  	case BTRFS_IOC_SNAP_CREATE:
>  		return btrfs_ioctl_snap_create(file, argp, 0, 0);
> -	case BTRFS_IOC_SNAP_CREATE_ASYNC:
> +	case BTRFS_IOC_SNAP_CREATE_V2:
>  		return btrfs_ioctl_snap_create(file, argp, 0, 1);
>  	case BTRFS_IOC_SUBVOL_CREATE:
>  		return btrfs_ioctl_snap_create(file, argp, 1, 0);
> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
> index 17c99eb..bc70584 100644
> --- a/fs/btrfs/ioctl.h
> +++ b/fs/btrfs/ioctl.h
> @@ -30,10 +30,14 @@ struct btrfs_ioctl_vol_args {
>  	char name[BTRFS_PATH_NAME_MAX + 1];
>  };
>  
> -#define BTRFS_SNAPSHOT_NAME_MAX 4079
> -struct btrfs_ioctl_async_vol_args {
> +#define BTRFS_SNAPSHOT_CREATE_ASYNC	(1ULL << 0)
> +
> +#define BTRFS_SNAPSHOT_NAME_MAX 4039
> +struct btrfs_ioctl_vol_args_v2 {
>  	__s64 fd;
>  	__u64 transid;
> +	__u64 flags;
> +	__u64 unused[4];
>  	char name[BTRFS_SNAPSHOT_NAME_MAX + 1];
>  };

Why the unused fields ? What happens if you use a more recent btrfs-tools 
which take advantage of these fields but the kernel is an old one ? At the 
minimum please check the flags so
	(flags^(BTRFS_SNAPSHOT_CREATE_ASYNC|BTRFS_SNAPSHOT_RDONLY)) == 0
and
	unused[0..3] == 0

For future expansion I suggest to use a different ioctl. To me it seems a more 
robust API.

>  
> @@ -187,6 +191,6 @@ struct btrfs_ioctl_space_args {
>  				    struct btrfs_ioctl_space_args)
>  #define BTRFS_IOC_START_SYNC _IOR(BTRFS_IOCTL_MAGIC, 24, __u64)
>  #define BTRFS_IOC_WAIT_SYNC  _IOW(BTRFS_IOCTL_MAGIC, 22, __u64)
> -#define BTRFS_IOC_SNAP_CREATE_ASYNC _IOW(BTRFS_IOCTL_MAGIC, 23, \
> -				   struct btrfs_ioctl_async_vol_args)
> +#define BTRFS_IOC_SNAP_CREATE_V2 _IOW(BTRFS_IOCTL_MAGIC, 23, \
> +				   struct btrfs_ioctl_vol_args_v2)

I repeat: great work, please take my comments only a suggestion to improve 
instead of an empty criticism.

Regards
G.Baroncelli

>  #endif
> -- 
> 1.6.3
> 
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