Revert "btrfs: add ioctl to export size of global metadata reservation"

This reverts commit 01e219e8.

David Sterba found a different way to provide these features without adding a new
ioctl.  We haven't released any progs with this ioctl yet, so I'm taking this out
for now until we finalize things.
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
CC: Jeff Mahoney <jeffm@suse.com>

fs/btrfs/ioctl.c

@@ -3559,20 +3559,6 @@ static long btrfs_ioctl_space_info(struct btrfs_root *root, void __user *arg)
 	return ret;
 }
 
-static long btrfs_ioctl_global_rsv(struct btrfs_root *root, void __user *arg)
-{
-	struct btrfs_block_rsv *block_rsv = &root->fs_info->global_block_rsv;
-	u64 reserved;
-
-	spin_lock(&block_rsv->lock);
-	reserved = block_rsv->reserved;
-	spin_unlock(&block_rsv->lock);
-
-	if (arg && copy_to_user(arg, &reserved, sizeof(reserved)))
-		return -EFAULT;
-	return 0;
-}
-
 /*
  * there are many ways the trans_start and trans_end ioctls can lead
  * to deadlocks.  They should only be used by applications that
@@ -4779,8 +4765,6 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_logical_to_ino(root, argp);
 	case BTRFS_IOC_SPACE_INFO:
 		return btrfs_ioctl_space_info(root, argp);
-	case BTRFS_IOC_GLOBAL_RSV:
-		return btrfs_ioctl_global_rsv(root, argp);
 	case BTRFS_IOC_SYNC: {
 		int ret;
 

include/uapi/linux/btrfs.h

@@ -558,7 +558,6 @@ static inline char *btrfs_err_str(enum btrfs_err_code err_code)
 #define BTRFS_IOC_DEFAULT_SUBVOL _IOW(BTRFS_IOCTL_MAGIC, 19, __u64)
 #define BTRFS_IOC_SPACE_INFO _IOWR(BTRFS_IOCTL_MAGIC, 20, \
 				    struct btrfs_ioctl_space_args)
-#define BTRFS_IOC_GLOBAL_RSV _IOR(BTRFS_IOCTL_MAGIC, 20, __u64)
 #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_V2 _IOW(BTRFS_IOCTL_MAGIC, 23, \