f2fs: add ioctl to expose current features

This patch adds an ioctl to provide feature information to user.
For exapmle, SQLite can use this ioctl to detect whether f2fs support atomic
write or not.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -112,6 +112,7 @@ struct f2fs_mount_info {
 
 #define F2FS_FEATURE_ENCRYPT	0x0001
 #define F2FS_FEATURE_BLKZONED	0x0002
+#define F2FS_FEATURE_ATOMIC_WRITE 0x0004
 
 #define F2FS_HAS_FEATURE(sb, mask)					\
 	((F2FS_SB(sb)->raw_super->feature & cpu_to_le32(mask)) != 0)
@@ -308,6 +309,7 @@ static inline bool __has_cursum_space(struct f2fs_journal *journal,
 						struct f2fs_flush_device)
 #define F2FS_IOC_GARBAGE_COLLECT_RANGE	_IOW(F2FS_IOCTL_MAGIC, 11,	\
 						struct f2fs_gc_range)
+#define F2FS_IOC_GET_FEATURES		_IOR(F2FS_IOCTL_MAGIC, 12, __u32)
 
 #define F2FS_IOC_SET_ENCRYPTION_POLICY	FS_IOC_SET_ENCRYPTION_POLICY
 #define F2FS_IOC_GET_ENCRYPTION_POLICY	FS_IOC_GET_ENCRYPTION_POLICY

fs/f2fs/file.c

@@ -2401,6 +2401,16 @@ out:
 	return ret;
 }
 
+static int f2fs_ioc_get_features(struct file *filp, unsigned long arg)
+{
+	struct inode *inode = file_inode(filp);
+	u32 sb_feature = le32_to_cpu(F2FS_I_SB(inode)->raw_super->feature);
+
+	/* Must validate to set it with SQLite behavior in Android. */
+	sb_feature |= F2FS_FEATURE_ATOMIC_WRITE;
+
+	return put_user(sb_feature, (u32 __user *)arg);
+}
 
 long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
@@ -2443,6 +2453,8 @@ long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return f2fs_ioc_move_range(filp, arg);
 	case F2FS_IOC_FLUSH_DEVICE:
 		return f2fs_ioc_flush_device(filp, arg);
+	case F2FS_IOC_GET_FEATURES:
+		return f2fs_ioc_get_features(filp, arg);
 	default:
 		return -ENOTTY;
 	}
@@ -2508,6 +2520,7 @@ long f2fs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	case F2FS_IOC_DEFRAGMENT:
 	case F2FS_IOC_MOVE_RANGE:
 	case F2FS_IOC_FLUSH_DEVICE:
+	case F2FS_IOC_GET_FEATURES:
 		break;
 	default:
 		return -ENOIOCTLCMD;