btrfs: add ioctls to query/change feature bits online

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, as well as querying for which features are changeable with mounted.
- BTRFS_IOC_SET_FEATURES: change features on a per-fs basis.

We introduce two new masks per feature set (_SAFE_SET and _SAFE_CLEAR) that
allow us to define which features are safe to change at runtime.

The failure modes for BTRFS_IOC_SET_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

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 45e618921c61..b4d69092fbdb 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -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
@@ -606,5 +612,11 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
                                     struct btrfs_ioctl_dev_replace_args)
 #define BTRFS_IOC_FILE_EXTENT_SAME _IOWR(BTRFS_IOCTL_MAGIC, 54, \
                                          struct btrfs_ioctl_same_args)
+#define BTRFS_IOC_GET_FEATURES _IOR(BTRFS_IOCTL_MAGIC, 57, \
+                                   struct btrfs_ioctl_feature_flags)
+#define BTRFS_IOC_SET_FEATURES _IOW(BTRFS_IOCTL_MAGIC, 57, \
+                                   struct btrfs_ioctl_feature_flags[2])
+#define BTRFS_IOC_GET_SUPPORTED_FEATURES _IOR(BTRFS_IOCTL_MAGIC, 57, \
+                                   struct btrfs_ioctl_feature_flags[3])
 
 #endif /* _UAPI_LINUX_BTRFS_H */