ioctl_userfaultfd.2: Rework formatting of structures for each ioctl() operation

Trying to place structure names on the same line as the ioctl()
operation names makes the lines two busy. And, conventionally,
the space after a hanging-list constant name is optionally used
to indicate the kernel version number where the constant was
introduced..

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/ioctl_userfaultfd.2

@@ -60,11 +60,13 @@ operations described below are used to configure userfaultfd behavior.
 They allow the caller to choose what features will be enabled and
 what kinds of events will be delivered to the application.
 .TP
-.BR "UFFDIO_API 	struct uffdio_api *" argp
+.BR UFFDIO_API
 Enable operation of the userfaultfd and perform API handshake.
 The
-.I uffdio_api
-structure is defined as:
+.I argp
+argument is a pointer to a
+.IR uffdio_api
+structure, defined as:
 .in +4n
 .nf
 
@@ -105,11 +107,13 @@ The
 operation has already been performed on this userfaultfd file descriptor.
 .RE
 .TP
-.BI "UFFDIO_REGISTER 	struct uffdio_register *" argp
+.B UFFDIO_REGISTER
 Register a memory address range with the userfaultfd object.
 The
+.I argp
+argument is a pointer to a
 .I uffdio_register
-structure is defined as:
+structure, defined as:
 .in +4n
 .nf
 
@@ -160,7 +164,7 @@ range in the
 field.
 .\"
 .TP
-.BI "UFFDIO_UNREGISTER  	struct uffdio_register *" argp
+.B UFFDIO_UNREGISTER
 Unregister a memory address range from userfaultfd.
 The address range to unregister is specified in the
 .IR uffdio_range
@@ -199,14 +203,16 @@ operations enable the calling application to resolve page fault
 events in a consistent way.
 .\" FIXME What does "consistent" mean?
 .TP
-.BI "UFFDIO_COPY 	struct uffdio_copy *" argp
+.B UFFDIO_COPY
 Atomically copy a continuous memory chunk into the userfault registered
 range and optionally wake up the blocked thread.
 The source and destination addresses and the number of bytes to copy are
 specified by the
 .IR src ", " dst ", and " len
-fields of
-.IR "struct uffdio_copy" :
+fields of the
+.I uffdio_copy
+structure pointed to by
+.IR argp :
 
 .in +4n
 .nf
@@ -263,13 +269,14 @@ it is not read by the
 operation.
 .\"
 .TP
-.BI "UFFDIO_ZERO 	struct uffdio_zero *" argp
+.B UFFDIO_ZERO
 Zero out a part of memory range registered with userfaultfd.
 The requested range is specified by the
 .I range
 field of the
 .I uffdio_zeropage
-structure:
+structure pointed to by
+.IR argp :
 
 .in +4n
 .nf
@@ -303,8 +310,13 @@ or an error in the same manner as
 .IR uffdio_copy.copy .
 .\"
 .TP
-.BI "UFFDIO_WAKE 	struct uffdio_range *" argp
+.B UFFDIO_WAKE
 Wake up the thread waiting for page-fault resolution.
+The
+.I argp
+argument is a pointer to a
+.I uffdio_range
+structure (shown above).
 .\" FIXME: Need more detail here. What is the purpose of the
 .\" 'struct uffdio_range *' argument?