fs: Add new pre-allocation ioctls to vfs for compatibility with legacy xfs ioctls

This patch adds ioctls to vfs for compatibility with legacy XFS
pre-allocation ioctls (XFS_IOC_*RESVP*). The implementation
effectively invokes sys_fallocate for the new ioctls.
Also handles the compat_ioctl case.
Note: These legacy ioctls are also implemented by OCFS2.

[AV: folded fixes from hch]

Signed-off-by: Ankit Jain <me@ankitjain.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/falloc.h

diff --git a/include/linux/falloc.h b/include/linux/falloc.h
index 8e912ab..3c15510 100644
--- a/include/linux/falloc.h
+++ b/include/linux/falloc.h
@@ -3,4 +3,25 @@
 
 #define FALLOC_FL_KEEP_SIZE	0x01 /* default is extend size */
 
+#ifdef __KERNEL__
+
+/*
+ * Space reservation ioctls and argument structure
+ * are designed to be compatible with the legacy XFS ioctls.
+ */
+struct space_resv {
+	__s16		l_type;
+	__s16		l_whence;
+	__s64		l_start;
+	__s64		l_len;		/* len == 0 means until end of file */
+	__s32		l_sysid;
+	__u32		l_pid;
+	__s32		l_pad[4];	/* reserved area */
+};
+
+#define FS_IOC_RESVSP		_IOW('X', 40, struct space_resv)
+#define FS_IOC_RESVSP64		_IOW('X', 42, struct space_resv)
+
+#endif /* __KERNEL__ */
+
 #endif /* _FALLOC_H_ */