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C Library Reference
I
inet6_rthdr_space()
Determine the space required by an IPv6 routing header

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        Internet Control Message Protocol for IP6
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        Internet protocol version 6 family
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        Append IPv6 hop-by-hop or destination options into ancillary data object
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        Append an IPv6 hop-by-hop or destination option to an ancillary data object
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        Search for IPv6 hop-by-hop and destination options
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        Initialize an ancillary data object that contains IPv6 hop-by-hop and destination options
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        Find the next IPv6 hop-by-hop or destination option
      - inet6_option_space()
        Determine how much space an IPv6 hop-by-hop or destination option requires
      - inet6_rthdr_add()
        Add an address to an IPv6 routing header
      - inet6_rthdr_getaddr()
        Get a pointer to an IPv6 address in the routing header
      - inet6_rthdr_getflags()
        Get the flags for a segment in an IPv6 routing header
      - inet6_rthdr_init()
        Initialize an IPv6 routing header
      - inet6_rthdr_lasthop()
        Specify the Strict/Loose flag for the final hop of an IPv6 routing header
      - inet6_rthdr_reverse()
        Reverse the list of addresses in an IPv6 router header
      - inet6_rthdr_segments()
        Count the segments in an IPv6 routing header
      - inet6_rthdr_space()
        Determine the space required by an IPv6 routing header
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        Check access permissions
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        Handle an _IO_CHMOD message
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        Default handler for _IO_CHMOD messages
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        Default handler for _IO_DEVCTL messages
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        Handle an _IO_FDINFO message
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        Default handler for _IO_FDINFO messages
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        Default handler for _IO_CONNECT messages
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        Increment count and locking flags
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        Default handler for _IO_OPENFD messages
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        Support pathconf() requests
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        Default handler for _IO_PATHCONF messages
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        Default handler for _IO_READ messages
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        Verify a client's read access to a resource
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        Verify the attributes being used to read a link
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        Do permission checks for a _IO_CONNECT_RENAME message
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        Do permission checks for the _IO_SPACE message
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        Populate a stat structure
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        Default handler for _IO_STAT messages
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        Indicate if synchronization is needed
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        Default handler for _IO_SYNC messages
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        Verify permissions to sync
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        Update time stamps
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        Unblock OCBs
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        Default unblock handler
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        Verify that an entry can be unlinked
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        Default handler for the unlock_ocb callout
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        Update time stamps
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        Default handler for _IO_UTIME messages
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        Default handler for _IO_WRITE messages
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        Verify a client's write access to a resource
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        Arm a resource manager
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        Internet Protocol
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        Internet security protocol
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        Generate a readable string from an IPsec policy specification
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        Get the length of the IPsec policy
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        Generate an IPsec policy specification structure from a readable string
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        Error messages for IPsec policy manipulation library
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        Internet Protocol version 6
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        Test a character to see if it's alphanumeric
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        Test a character to see if it's a 7-bit ASCII character
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        Test to see if a file descriptor is associated with a terminal
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        Test a character to see if it's a blank character
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        Test a character to see if it's a control character
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        Test a character to see if it's a decimal digit
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        Test the file type of a file descriptor
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        Determine if a number is finite
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        Test a character to see if it's any printable character except a space
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        Determine whether one floating-point number is greater than another
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        Determine whether one floating-point number is greater than or equal to another
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        Test for infinity
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        Determine whether one floating-point number is less than another
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        Determine whether one floating-point number is less than or equal to another
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        Determine whether one floating-point number is less than or greater than another
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        Test a character to see if it's a lowercase letter
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        Test for not-a-number (NaN)
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        Determine whether a floating-point number is normal
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        Test a character to see if it's a whitespace character
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        Determine whether two floating-point numbers are unordered
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        Convert an integer into a string, using a given base
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inet6_rthdr_space()

Determine the space required by an IPv6 routing header

Synopsis:

#include <netinet/in.h>

size_t inet6_rthdr_space(int type, 
                         int segments);

Arguments:

type: The type of IPv6 routing header (e.g., Type 0 as defined in <netinet/in.h>).
segments: The number of segments (addresses) in the routing header.

Library:

libsocket

Use the -l socket option to qcc to link against this library.

Description:

This function returns the number of bytes required to hold a routing header of the specified type containing a specified number of segments (addresses). For an IPv6 Type 0 routing header, the number of segments must be between 1 and 23, inclusive. The return value includes the size of the cmsghdr structure that precedes the routing header, and any required padding.

Note:

This function returns the size but doesn't allocate the space required for the ancillary data. This allows an application to allocate a larger buffer, if other ancillary data objects are desired. All the ancillary data objects must be specified to sendmsg() as a single msg_control buffer in the msghdr structure msg_control member.

Based on:

W. Stevens and M. Thomas, Advanced Sockets API for IPv6, RFC 2292, February 1998. Contains good examples.
S. Deering and R. Hinden, Internet Protocol, Version 6 (IPv6) Specification, RFC 2460, December 1998.

Returns:

The number of bytes required, or 0 if the type of the routing header isn't supported by this implementation or the number of segments is invalid for this type of routing header.

Classification:


Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Yes

Page updated: March 12, 2026