ioctl_userfaultfd.2: Rework list of ioctl() operations as subsections

Mainly, this means that we drop one level of indentation, which is
useful, since the error lists also add a level of indentation,
and the text overall becomes a little overindented.

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

man2/ioctl_userfaultfd.2

@@ -72,9 +72,8 @@ operations.
 These operations enable the calling application to resolve page fault
 events in a consistent way.
 .\" FIXME What does "consistent" mean?
-
-.TP
-.BR UFFDIO_API
+.\"
+.SS UFFDIO_API
 Enable operation of the userfaultfd and perform API handshake.
 The
 .I argp
@@ -113,15 +112,13 @@ On error, \-1 is returned and
 .I errno
 is set to indicate the cause of the error.
 Possible errors include:
-.RS
 .TP
 .B EINVAL
 The
 .B UFFDIO_API
 operation has already been performed on this userfaultfd file descriptor.
-.RE
-.TP
-.B UFFDIO_REGISTER
+.\"
+.SS UFFDIO_REGISTER
 Register a memory address range with the userfaultfd object.
 The
 .I argp
@@ -158,8 +155,6 @@ The
 field defines the mode of operation desired for this memory region.
 The following values may be bitwise ORed to set the userfaultfd mode for
 the specified range:
-
-.RS
 .TP
 .B UFFDIO_REGISTER_MODE_MISSING
 Track page faults on missing pages
@@ -168,8 +163,7 @@ Track page faults on missing pages
 Track page faults on write-protected pages.
 Currently, the only supported mode is
 .BR UFFDIO_REGISTER_MODE_MISSING .
-.RE
-.IP
+.PP
 .\" FIXME In the following, what does "answers" mean, and what are the bits?
 .\" (we need a list of the bits here).
 The kernel answers which ioctl commands are available for the requested
@@ -177,8 +171,7 @@ range in the
 .I ioctls
 field.
 .\"
-.TP
-.B UFFDIO_UNREGISTER
+.SS UFFDIO_UNREGISTER
 Unregister a memory address range from userfaultfd.
 The address range to unregister is specified in the
 .IR uffdio_range
@@ -192,7 +185,6 @@ On error, \-1 is returned and
 .I errno
 is set to indicate the cause of the error.
 Possible errors include:
-.RS
 .TP
 .B EINVAL
 Either the
@@ -208,9 +200,8 @@ There as an incompatible mapping in the specified address range.
 .TP
 .B EINVAL
 There was no mapping in the specified address range.
-.RE
-.TP
-.B UFFDIO_COPY
+.\"
+.SS 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
@@ -232,19 +223,16 @@ struct uffdio_copy {
 };
 .fi
 .in
-.IP
+.PP
 The following values may be bitwise ORed in
 .IR mode
 to change the behavior of the
 .B UFFDIO_COPY
 operation:
-
-.RS
 .TP
 .B UFFDIO_COPY_MODE_DONTWAKE
 Do not wake up the thread that waits for page fault resolution
-.RE
-.IP
+.PP
 The
 .I copy
 field of the
@@ -275,8 +263,7 @@ it is not read by the
 .B UFFDIO_COPY
 operation.
 .\"
-.TP
-.B UFFDIO_ZERO
+.SS UFFDIO_ZERO
 Zero out a part of memory range registered with userfaultfd.
 The requested range is specified by the
 .I range
@@ -294,19 +281,16 @@ struct uffdio_zeropage {
 };
 .fi
 .in
-.IP
+.PP
 The following values may be bitwise ORed in
 .IR mode
 to change the behavior of
 .B UFFDIO_ZERO
 operation:
-
-.RS
 .TP
 .B UFFDIO_ZEROPAGE_MODE_DONTWAKE
 Do not wake up the thread that waits for page-fault resolution.
-.RE
-.IP
+.PP
 The
 .I zeropage
 field of the
@@ -316,8 +300,7 @@ that was actually zeroed,
 or an error in the same manner as
 .IR uffdio_copy.copy .
 .\"
-.TP
-.B UFFDIO_WAKE
+.SS UFFDIO_WAKE
 Wake up the thread waiting for page-fault resolution.
 The
 .I argp
@@ -334,7 +317,6 @@ On error, \-1 is returned and
 .I errno
 is set to indicate the cause of the error.
 Possible errors include:
-.RS
 .TP
 .B EINVAL
 Either the
@@ -344,7 +326,6 @@ or the
 field of the
 .I ufdio_range
 structure was not a multiple of the system page size.
-.RE
 .SH RETURN VALUE
 See descriptions of the individual operations, above.
 .SH ERRORS