On Tue, 27 Aug 2013 15:17:54 -0400, Jeff Mahoney wrote:
> There are some feature bits that require no offline setup and can
> be enabled online. I've only reviewed extended irefs, but there will
> probably be more.
>
> We introduce three new ioctls:
> - BTRFS_IOC_GET_SUPPORTED_FEATURES: query the kernel for supported features
> - BTRFS_IOC_GET_FEATURES: query the kernel for enabled features on a per-fs
> basis.
> - BTRFS_IOC_ADD_FEATURES: enable new features on a per-fs basis.
>
> We introduce a new mask _SAFE_ONLINE that allows us to define which
> features are safe to enable at runtime.
>
> The failure modes for BTRFS_IOC_ADD_FEATURES are as follows:
> - Enabling a completely unsupported feature: warns and returns -ENOTSUPP
> - Enabling a feature that can only be done offline: warns and returns -EPERM
>
> The structure passed in is not modified on return since it is possible
> to isolate which features would bounce a -EPERM by subtracting the features
> provided by a GET_SUPPORTED_FEATURES call.
>
> Signed-off-by: Jeff Mahoney <je...@suse.com>
[...]
> --- a/include/uapi/linux/btrfs.h 2013-08-27 11:02:35.062626912 -0400
> +++ b/include/uapi/linux/btrfs.h 2013-08-27 11:03:32.006352802 -0400
> @@ -184,6 +184,12 @@ struct btrfs_ioctl_fs_info_args {
> __u64 reserved[124]; /* pad to 1k */
> };
>
> +struct btrfs_ioctl_feature_flags {
> + __u64 compat_flags;
> + __u64 compat_ro_flags;
> + __u64 incompat_flags;
> +};
> +
> /* balance control ioctl modes */
> #define BTRFS_BALANCE_CTL_PAUSE 1
> #define BTRFS_BALANCE_CTL_CANCEL 2
> @@ -579,4 +585,10 @@ static inline char *btrfs_err_str(enum b
> struct btrfs_ioctl_get_dev_stats)
> #define BTRFS_IOC_DEV_REPLACE _IOWR(BTRFS_IOCTL_MAGIC, 53, \
> struct btrfs_ioctl_dev_replace_args)
> +#define BTRFS_IOC_GET_FEATURES _IOR(BTRFS_IOCTL_MAGIC, 54, \
> + struct btrfs_ioctl_feature_flags)
> +#define BTRFS_IOC_ADD_FEATURES _IOW(BTRFS_IOCTL_MAGIC, 55, \
> + struct btrfs_ioctl_feature_flags)
#define BTRFS_IOC_ADD_FEATURES _IOW(BTRFS_IOCTL_MAGIC, 54, \
struct btrfs_ioctl_feature_flags)
Using 54 for both would also be possible since the directions are
different. _IOR(54) for the get ioctl and _IOW(54) for the set/add ioctl.
> +#define BTRFS_IOC_GET_SUPPORTED_FEATURES _IOR(BTRFS_IOCTL_MAGIC, 56, \
> + struct btrfs_ioctl_feature_flags[2])
This could share the type value 54 too, since the parameter size is
different. There are only 8 bits for the type field.
And in order to support clearing feature bits you could replace the add
ioctl with a set ioctl and use a mask + value scheme.
#define BTRFS_IOC_SET_FEATURES _IOW(BTRFS_IOCTL_MAGIC, 54, \
struct btrfs_ioctl_feature_flags[2])
btrfs_ioctl_feature_flags[0] is the mask and
btrfs_ioctl_feature_flags[1] is the value. Only bits that are set to one
in the mask are taken from the value and modified in the filesystem flags.
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