syscalls.2: Add system calls that are new in 5.13

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

man1/ldd.1

@@ -23,14 +23,11 @@ ldd \- print shared object dependencies
 prints the shared objects (shared libraries) required by each program or
 shared object specified on the command line.
 An example of its use and output
-(using
-.BR sed (1)
-to trim leading white space for readability in this page)
 is the following:
 .PP
 .in +4n
 .EX
-$ \fBldd /bin/ls | sed \(aqs/^ */    /\(aq\fP
+$ \fBldd /bin/ls\fP
     linux\-vdso.so.1 (0x00007ffcc3563000)
     libselinux.so.1 => /lib64/libselinux.so.1 (0x00007f87e5459000)
     libcap.so.2 => /lib64/libcap.so.2 (0x00007f87e5254000)

man1/localedef.1

@@ -245,7 +245,8 @@ and
 .IR intcurrsym .
 .TP
 .B \-\-posix
-Conform strictly to POSIX.  Implies
+Conform strictly to POSIX.
+Implies
 .BR \-\-verbose .
 This option currently has no other effect.
 POSIX conformance is assumed if the environment variable

man2/access.2

@@ -358,8 +358,8 @@ call will still fail.
 These calls
 may not work correctly on NFSv2 filesystems with UID mapping enabled,
 because UID mapping is done on the server and hidden from the client,
-which checks permissions.  (NFS versions 3 and higher perform the check on
-the server.)
+which checks permissions.
+(NFS versions 3 and higher perform the check on the server.)
 Similar problems can occur to FUSE mounts.
 .\"
 .\"

man2/close_range.2

@@ -33,9 +33,6 @@ close_range \- close all file descriptors in a given range
 .BI "int close_range(unsigned int " first ", unsigned int " last ,
 .BI "                unsigned int " flags );
 .fi
-.PP
-.IR Note :
-There is no glibc wrapper for this system call; see NOTES.
 .SH DESCRIPTION
 The
 .BR close_range ()
@@ -100,8 +97,6 @@ Library support was added in glibc in version 2.34.
 .BR close_range ()
 is a nonstandard function that is also present on FreeBSD.
 .SH NOTES
-Glibc does not provide a wrapper for this system call; call it using
-.BR syscall (2).
 .SS Closing all open file descriptors
 .\" 278a5fbaed89dacd04e9d052f4594ffd0e0585de
 To avoid blindly closing file descriptors

man2/ioctl_console.2

@@ -685,7 +685,8 @@ These are legal only for the superuser or the owner of the current terminal.
 .TP
 .B "TIOCLINUX, subcode=0"
 Dump the screen.
-Disappeared in Linux 1.1.92.  (With kernel 1.1.92 or later, read from
+Disappeared in Linux 1.1.92.
+(With kernel 1.1.92 or later, read from
 .I /dev/vcsN
 or
 .I /dev/vcsaN

man2/ioctl_fslabel.2

@@ -43,7 +43,8 @@ The
 operation requires privilege
 .RB ( CAP_SYS_ADMIN ).
 .SH RETURN VALUE
-On success zero is returned.  On error, \-1 is returned, and
+On success zero is returned.
+On error, \-1 is returned, and
 .I errno
 is set to indicate the error.
 .SH ERRORS
@@ -77,7 +78,8 @@ The maximum string length for this interface is
 .BR FSLABEL_MAX ,
 including the terminating null byte (\(aq\\0\(aq).
 Filesystems have differing maximum label lengths, which may or
-may not include the terminating null.  The string provided to
+may not include the terminating null.
+The string provided to
 .B FS_IOC_SETFSLABEL
 must always be null-terminated, and the string returned by
 .B FS_IOC_GETFSLABEL

man2/ioctl_tty.2

@@ -71,6 +71,67 @@ Equivalent to
 Allow the output buffer to drain, discard pending input, and
 set the current serial port settings.
 .PP
+The following four ioctls, added in Linux 2.6.20,
+.\" commit 64bb6c5e1ddcd47c951740485026ef08975ee2e6
+.\" commit 592ee3a5e5e2a981ef2829a0380093006d045661
+are just like
+.BR TCGETS ,
+.BR TCSETS ,
+.BR TCSETSW ,
+.BR TCSETSF ,
+except that they take a
+.I "struct termios2\ *"
+instead of a
+.IR "struct termios\ *" .
+If the structure member
+.B c_cflag
+contains the flag
+.BR BOTHER ,
+then the baud rate is stored in the structure members
+.B c_ispeed
+and
+.B c_ospeed
+as integer values.
+These ioctls are not supported on all architectures.
+.RS
+.TS
+lb l.
+TCGETS2	\fBstruct termios2 *\fPargp
+TCSETS2	\fBconst struct termios2 *\fPargp
+TCSETSW2	\fBconst struct termios2 *\fPargp
+TCSETSF2	\fBconst struct termios2 *\fPargp
+.TE
+.RE
+.PP
+The following four ioctls are just like
+.BR TCGETS ,
+.BR TCSETS ,
+.BR TCSETSW ,
+.BR TCSETSF ,
+except that they take a
+.I "struct termios2\ *"
+instead of a
+.IR "struct termios\ *" .
+If the structure member
+.B c_cflag
+contains the flag
+.B BOTHER
+then, the baud rate is stored in the structure members
+.B c_ispeed
+and
+.B c_ospeed
+as integer values.
+These ioctls are not supported on all architectures.
+.RS
+.TS
+lb l.
+TCGETS2	\fBstruct termios2 *\fPargp
+TCSETS2	\fBconst struct termios2 *\fPargp
+TCSETSW2	\fBconst struct termios2 *\fPargp
+TCSETSF2	\fBconst struct termios2 *\fPargp
+.TE
+.RE
+.PP
 The following four ioctls are just like
 .BR TCGETS ,
 .BR TCSETS ,
@@ -701,7 +762,8 @@ Insufficient permission.
 Check the condition of DTR on the serial port.
 .PP
 .EX
-#include <termios.h>
+#include <stdio.h>
+#include <unistd.h>
 #include <fcntl.h>
 #include <sys/ioctl.h>
 

man2/openat2.2

@@ -439,7 +439,8 @@ call.
 .B EAGAIN
 .BR RESOLVE_CACHED
 was set, and the open operation cannot be performed using only cached
-information. The caller should retry without
+information.
+The caller should retry without
 .B RESOLVE_CACHED
 set in
 .I how.resolve .

man2/readv.2

@@ -141,9 +141,7 @@ are atomic: the data written by
 .\" Regarding atomicity, see https://bugzilla.kernel.org/show_bug.cgi?id=10596
 .BR writev ()
 is written as a single block that is not intermingled with output
-from writes in other processes (but see
-.BR pipe (7)
-for an exception);
+from writes in other processes;
 analogously,
 .BR readv ()
 is guaranteed to read a contiguous block of data from the file,

man2/sigaction.2

@@ -261,6 +261,44 @@ This flag is meaningful only when establishing a signal handler.
 .\" .I sa_sigaction
 .\" field was added in Linux 2.1.86.)
 .\"
+.TP
+.B SA_UNSUPPORTED
+Used to dynamically probe for flag bit support.
+.IP
+If an attempt to register a handler succeeds with this flag set in
+.I act\->sa_flags
+alongside other flags that are potentially unsupported by the kernel,
+and an immediately subsequent
+.BR sigaction ()
+call specifying the same signal number and with a non-NULL
+.I oldact
+argument yields
+.B SA_UNSUPPORTED
+.I clear
+in
+.IR oldact->sa_flags ,
+then
+.I oldact->sa_flags
+may be used as a bitmask
+describing which of the potentially unsupported flags are,
+in fact, supported.
+See the section "Dynamically probing for flag bit support"
+below for more details.
+.TP
+.BR SA_EXPOSE_TAGBITS " (since Linux 5.11)"
+Normally, when delivering a signal,
+an architecture-specific set of tag bits are cleared from the
+.I si_addr
+field of
+.IR siginfo_t .
+If this flag is set,
+an architecture-specific subset of the tag bits will be preserved in
+.IR si_addr .
+.IP
+Programs that need to be compatible with Linux versions older than 5.11
+must use
+.B SA_UNSUPPORTED
+to probe for support.
 .SS The siginfo_t argument to a SA_SIGINFO handler
 When the
 .B SA_SIGINFO
@@ -846,6 +884,61 @@ Triggered by a
 .BR seccomp (2)
 filter rule.
 .RE
+.SS Dynamically probing for flag bit support
+The
+.BR sigaction ()
+call on Linux accepts unknown bits set in
+.I act\->sa_flags
+without error.
+The behavior of the kernel starting with Linux 5.11 is that a second
+.BR sigaction ()
+will clear unknown bits from
+.IR oldact\->sa_flags .
+However, historically, a second
+.BR sigaction ()
+call would typically leave those bits set in
+.IR oldact\->sa_flags .
+.PP
+This means that support for new flags cannot be detected
+simply by testing for a flag in
+.IR sa_flags ,
+and a program must test that
+.B SA_UNSUPPORTED
+has been cleared before relying on the contents of
+.IR sa_flags .
+.PP
+Since the behavior of the signal handler cannot be guaranteed
+unless the check passes,
+it is wise to either block the affected signal
+while registering the handler and performing the check in this case,
+or where this is not possible,
+for example if the signal is synchronous, to issue the second
+.BR sigaction ()
+in the signal handler itself.
+.PP
+In kernels that do not support a specific flag,
+the kernel's behavior is as if the flag was not set,
+even if the flag was set in
+.IR act\->sa_flags .
+.PP
+The flags
+.BR SA_NOCLDSTOP ,
+.BR SA_NOCLDWAIT ,
+.BR SA_SIGINFO ,
+.BR SA_ONSTACK ,
+.BR SA_RESTART ,
+.BR SA_NODEFER ,
+.BR SA_RESETHAND ,
+and, if defined by the architecture,
+.B SA_RESTORER
+may not be reliably probed for using this mechanism,
+because they were introduced before Linux 5.11.
+However, in general, programs may assume that these flags are supported,
+since they have all been supported since Linux 2.6,
+which was released in the year 2003.
+.PP
+See EXAMPLES below for a demonstration of the use of
+.BR SA_UNSUPPORTED .
 .SH RETURN VALUE
 .BR sigaction ()
 returns 0 on success; on error, \-1 is returned, and
@@ -1051,6 +1144,49 @@ This bug was fixed in kernel 2.6.14.
 .SH EXAMPLES
 See
 .BR mprotect (2).
+.SS Probing for flag support
+The following example program exits with status
+.B EXIT_SUCCESS
+if
+.B SA_EXPOSE_TAGBITS
+is determined to be supported, and
+.B EXIT_FAILURE
+otherwise.
+.PP
+.EX
+#include <signal.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+
+void
+handler(int signo, siginfo_t *info, void *context)
+{
+    struct sigaction oldact;
+
+    if (sigaction(SIGSEGV, NULL, &oldact) == \-1 ||
+            (oldact.sa_flags & SA_UNSUPPORTED) ||
+            !(oldact.sa_flags & SA_EXPOSE_TAGBITS)) {
+        _exit(EXIT_FAILURE);
+    }
+    _exit(EXIT_SUCCESS);
+}
+
+int
+main(void)
+{
+    struct sigaction act = { 0 };
+
+    act.sa_flags = SA_SIGINFO | SA_UNSUPPORTED | SA_EXPOSE_TAGBITS;
+    act.sa_sigaction = &handler;
+    if (sigaction(SIGSEGV, &act, NULL) == \-1) {
+        perror("sigaction");
+        exit(EXIT_FAILURE);
+    }
+
+    raise(SIGSEGV);
+}
+.EE
 .SH SEE ALSO
 .BR kill (1),
 .BR kill (2),

man2/syscalls.2

@@ -412,6 +412,10 @@ T}
 .\" Was named sys_kexec_load() from 2.6.7 to 2.6.16
 \fBkeyctl\fP(2)	2.6.10
 \fBkill\fP(2)	1.0
+\fBlandlock_add_rule\fP(2)	5.13
+\fBlandlock_create_ruleset\fP(2)	5.13
+\fBlandlock_restrict_self\fP(2)	5.13
+\fBlandlock_add_rule\fP(2)	5.13
 \fBlchown\fP(2)	1.0	T{
 See \fBchown\fP(2) for
 version details
@@ -562,6 +566,7 @@ T}
 \fBpwritev2\fP(2)	4.6
 \fBquery_module\fP(2)	2.2	Removed in 2.6
 \fBquotactl\fP(2)	1.0
+\fBquotactl_path\fP(2)	5.13
 \fBread\fP(2)	1.0
 \fBreadahead\fP(2)	2.4.13
 \fBreaddir\fP(2)	1.0

man2/write.2

@@ -293,7 +293,8 @@ returning the number of bytes actually transferred.
 An error return value while performing
 .BR write ()
 using direct I/O does not mean the
-entire write has failed. Partial data may be written
+entire write has failed.
+Partial data may be written
 and the data at the file offset on which the
 .BR write ()
 was attempted should be considered inconsistent.

man3/dlsym.3

@@ -153,12 +153,15 @@ There are several scenarios when the address of a global symbol is NULL.
 For example, a symbol can be placed at zero address by the linker, via
 a linker script or with
 .I \-\-defsym
-command-line option. Undefined weak symbols also have NULL value.
+command-line option.
+Undefined weak symbols also have NULL value.
 Finally, the symbol value may be the result of
 a GNU indirect function (IFUNC) resolver function that returns
-NULL as the resolved value. In the latter case,
+NULL as the resolved value.
+In the latter case,
 .BR dlsym ()
-also returns NULL without error. However, in the former two cases, the
+also returns NULL without error.
+However, in the former two cases, the
 behavior of GNU dynamic linker is inconsistent: relocation processing
 succeeds and the symbol can be observed to have NULL value, but
 .BR dlsym ()

man3/getopt.3

@@ -130,7 +130,7 @@ A legitimate option character is any visible one byte
 .BR ascii (7)
 character (for which
 .BR isgraph (3)
-would return nonzero) that is not \(aq\-\(aq or \(aq:\(aq.
+would return nonzero) that is not \(aq\-\(aq, \(aq:\(aq, or \(aq;\(aq.
 If such a
 character is followed by a colon, the option requires an argument, so
 .BR getopt ()
@@ -166,9 +166,18 @@ If the first character of
 .B POSIXLY_CORRECT
 is set, then option processing stops as soon as a nonoption argument is
 encountered.
+If \(aq+\(aq is not the first character of
+.IR optstring ,
+it is treated as a normal option.
+If
+.B POSIXLY_CORRECT
+behaviour is required in this case
+.I optstring
+will contain two \(aq+\(aq symbols.
 If the first character of \fIoptstring\fP is \(aq\-\(aq, then
 each nonoption \fIargv\fP-element is handled as if it were the argument of
-an option with character code 1.  (This is used by programs that were
+an option with character code 1.
+(This is used by programs that were
 written to expect options and other \fIargv\fP-elements in any order
 and that care about the ordering of the two.)
 The special argument "\-\-" forces an end of option-scanning regardless

man3/nl_langinfo.3

@@ -111,7 +111,7 @@ conversion specification.)
 .BR T_FMT_AMPM \ (LC_TIME)
 Return a string that can be used as a format string for
 .BR strftime (3)
-to represent a time in a.m. or p.m. notation a locale-specific way
+to represent a time in a.m. or p.m. notation in a locale-specific way
 .RB ( %r
 conversion specification).
 .TP
@@ -200,7 +200,8 @@ for alternative representation of a time in a locale-specific way
 conversion specification).
 .TP
 .BR DAY_ "{1\(en7} (LC_TIME)"
-Return name of the \fIn\fP-th day of the week. [Warning: this follows
+Return name of the \fIn\fP-th day of the week.
+[Warning: this follows
 the US convention DAY_1 = Sunday, not the international convention
 (ISO 8601) that Monday is the first day of the week.]
 (Used in

man3/regex.3

@@ -66,8 +66,8 @@ All regular expression searching must be done via a compiled pattern
 buffer, thus
 .BR regexec ()
 must always be supplied with the address of a
-.BR regcomp ()
-initialized pattern buffer.
+.BR regcomp ()-initialized
+pattern buffer.
 .PP
 .I cflags
 is the

man3/termios.3

@@ -331,7 +331,8 @@ Ignore modem control lines.
 .TP
 .B LOBLK
 (not in POSIX) Block output from a noncurrent shell layer.
-For use by \fBshl\fP (shell layers).  (Not implemented on Linux.)
+For use by \fBshl\fP (shell layers).
+(Not implemented on Linux.)
 .TP
 .B CIBAUD
 (not in POSIX) Mask for input speeds.
@@ -945,24 +946,76 @@ to by \fItermios_p\fP to \fIspeed\fP, which must be one of these constants:
 	B57600
 	B115200
 	B230400
+	B460800
+	B500000
+	B576000
+	B921600
+	B1000000
+	B1152000
+	B1500000
+	B2000000
 .ft P
 .fi
 .PP
-The zero baud rate, \fBB0\fP,
+These constants are additionally supported on the SPARC architecture:
+.PP
+.nf
+.ft B
+	B76800
+	B153600
+	B307200
+	B614400
+.ft P
+.fi
+.PP
+These constants are additionally supported on non-SPARC architectures:
+.PP
+.nf
+.ft B
+	B2500000
+	B3000000
+	B3500000
+	B4000000
+.ft P
+.fi
+.PP
+Due to differences between architectures, portable applications should check
+if a particular
+.BI B nnn
+constant is defined prior to using it.
+.PP
+The zero baud rate,
+.BR B0 ,
 is used to terminate the connection.
 If B0 is specified, the modem control lines shall no longer be asserted.
 Normally, this will disconnect the line.
-\fBCBAUDEX\fP is a mask
+.B CBAUDEX
+is a mask
 for the speeds beyond those defined in POSIX.1 (57600 and above).
-Thus, \fBB57600\fP & \fBCBAUDEX\fP is nonzero.
+Thus,
+.BR B57600 " & " CBAUDEX
+is nonzero.
+.PP
+Setting the baud rate to a value other than those defined by
+.BI B nnn
+constants is possible via the
+.B TCSETS2
+ioctl; see
+.BR ioctl_tty (2).
 .PP
 .BR cfgetispeed ()
-returns the input baud rate stored in the \fItermios\fP structure.
+returns the input baud rate stored in the
+.I termios
+structure.
 .PP
 .BR cfsetispeed ()
-sets the input baud rate stored in the \fItermios\fP structure to
+sets the input baud rate stored in the
+.I termios
+structure to
 .IR speed ,
-which must be specified as one of the \fBBnnn\fP constants listed above for
+which must be specified as one of the
+.BI B nnn
+constants listed above for
 .BR cfsetospeed ().
 If the input baud rate is set to zero, the input baud rate will be
 equal to the output baud rate.
@@ -1056,8 +1109,14 @@ and
 are nonstandard, but available on the BSDs.
 .SH NOTES
 UNIX\ V7 and several later systems have a list of baud rates
-where after the fourteen values B0, ..., B9600 one finds the
-two constants EXTA, EXTB ("External A" and "External B").
+where after the values
+.BR B0
+through
+.B B9600
+one finds the two constants
+.BR EXTA ,
+.B EXTB
+("External A" and "External B").
 Many systems extend the list with much higher baud rates.
 .PP
 The effect of a nonzero \fIduration\fP with

man3/xcrypt.3

@@ -24,8 +24,8 @@ xencrypt, xdecrypt, passwd2des \- RFS password encryption
 .fi
 .SH DESCRIPTION
 .BR WARNING :
-Do not use these functions in new code. They do not achieve
-any type of acceptable cryptographic security guarantees.
+Do not use these functions in new code.
+They do not achieve any type of acceptable cryptographic security guarantees.
 .PP
 The function
 .BR passwd2des ()

man5/hosts.equiv.5

@@ -38,7 +38,8 @@ You can explicitly deny access to a host by preceding the
 .I hostname
 by a minus (\-) sign.
 Users from that host must always supply additional credentials,
-including possibly a password. For security reasons you should always
+including possibly a password.
+For security reasons you should always
 use the FQDN of the hostname and not the short hostname.
 .PP
 The

man5/nsswitch.conf.5

@@ -102,9 +102,10 @@ Shadow user passwords, used by
 .BR getspnam (3)
 and related functions.
 .PP
-The GNU C Library ignores databases with unknown names.  Some
-applications use this to implement special handling for their own
-databases.  For example,
+The GNU C Library ignores databases with unknown names.
+Some applications use this to implement special handling for their own
+databases.
+For example,
 .BR sudo (8)
 consults the
 .B sudoers

man7/cgroups.7

@@ -92,8 +92,8 @@ was eventually made official with the release of Linux 4.5.
 Differences between the two versions are described in the text below.
 The file
 .IR cgroup.sane_behavior ,
-present in cgroups v1, is a relic of this mount option. The file
-always reports "0" and is only retained for backward compatibility.
+present in cgroups v1, is a relic of this mount option.
+The file always reports "0" and is only retained for backward compatibility.
 .PP
 Although cgroups v2 is intended as a replacement for cgroups v1,
 the older system continues to exist

man7/man-pages.7

@@ -525,7 +525,8 @@ If there is a single such prototype that needs to be continued,
 then align the continuation line so that when the page is
 rendered on a fixed-width font device (e.g., on an xterm) the
 continuation line starts just below the start of the argument
-list in the line above.  (Exception: the indentation may be
+list in the line above.
+(Exception: the indentation may be
 adjusted if necessary to prevent a very long continuation line
 or a further continuation line where the function prototype is
 very long.)
@@ -541,7 +542,8 @@ As an example:
 But, where multiple functions in the SYNOPSIS require
 continuation lines, and the function names have different
 lengths, then align all continuation lines to start in the
-same column.  This provides a nicer rendering in PDF output
+same column.
+This provides a nicer rendering in PDF output
 (because the SYNOPSIS uses a variable width font where
 spaces render narrower than most characters).
 As an example:
@@ -638,7 +640,7 @@ makes it easier to write tools that parse man page source files.)
 .SS Use semantic newlines
 In the source of a manual page,
 new sentences should be started on new lines,
-and long sentences should split into lines at clause breaks
+and long sentences should be split into lines at clause breaks
 (commas, semicolons, colons, and so on).
 This convention, sometimes known as "semantic newlines",
 makes it easier to see the effect of patches,

man7/namespaces.7

@@ -71,7 +71,8 @@ Time	CLONE_NEWTIME	\fBtime_namespaces\fP(7)	T{
 Boot and monotonic
 clocks
 T}
-User	CLONE_NEWUSER	\fBuser_namespaces\fP(7)	T{User and group IDs
+User	CLONE_NEWUSER	\fBuser_namespaces\fP(7)	T{
+User and group IDs
 T}
 UTS	CLONE_NEWUTS	\fButs_namespaces\fP(7)	T{
 Hostname and NIS

man7/netlink.7

@@ -189,7 +189,8 @@ message signals an error and the payload contains an
 .I nlmsgerr
 structure,
 .B NLMSG_DONE
-message terminates a multipart message. Error messages get the
+message terminates a multipart message.
+Error messages get the
 original request appened, unless the user requests to cap the
 error message, and get extra error data if requested.
 .PP

man7/path_resolution.7

@@ -177,10 +177,11 @@ with the
 flag set (though note that this also restricts bind mount traversal).
 .SS Trailing slashes
 If a pathname ends in a \(aq/\(aq, that forces resolution of the preceding
-component as in Step 2: it has to exist and resolve to a directory.
+component as in Step 2:
+the component preceding the slash either exists and resolves to a directory
+of it names a directory that is to be created immediately after the
+pathname is resolved.
 Otherwise, a trailing \(aq/\(aq is ignored.
-(Or, equivalently, a pathname with a trailing \(aq/\(aq is equivalent to
-the pathname obtained by appending \(aq.\(aq to it.)
 .SS Final symlink
 If the last component of a pathname is a symbolic link, then it
 depends on the system call whether the file referred to will be

man7/pipe.7

@@ -244,9 +244,7 @@ and
 limits; see BUGS.
 .\"
 .SS PIPE_BUF
-POSIX.1 says that
-.BR write (2)s
-of less than
+POSIX.1 says that writes of less than
 .B PIPE_BUF
 bytes must be atomic: the output data is written to the pipe as a
 contiguous sequence.

man7/system_data_types.7

@@ -1247,7 +1247,8 @@ Alternatively,
 or
 .IR <wordexp.h> .
 .PP
-Used for a count of bytes.  It is the result of the
+Used for a count of bytes.
+It is the result of the
 .I sizeof
 operator.
 According to the C language standard,

man7/unix.7

@@ -819,7 +819,7 @@ reference to it is closed.
 To pass file descriptors or credentials over a
 .BR SOCK_STREAM
 socket, you must
-to send or receive at least one byte of nonancillary data in the same
+send or receive at least one byte of nonancillary data in the same
 .BR sendmsg (2)
 or
 .BR recvmsg (2)