Tribblix: manual page: mac_hcksum

MAC_HCKSUM_GET(9F) Kernel Functions for Drivers MAC_HCKSUM_GET(9F)

NAME

mac_hcksum_get, mac_hcksum_set - get and set checksum information on
message blocks

SYNOPSIS

#include <sys/mac_provider.h>

void
mac_hcksum_get(const mblk_t *mp, uint32_t *start, uint32_t *stuff,
uint32_t *end, uint32_t *value, uint32_t *flags);

void
mac_hcksum_set(mblk_t *mp, uint32_t start, uint32_t stuff,
uint32_t end, uint32_t value, uint32_t flags);

INTERFACE LEVEL

illumos DDI specific

PARAMETERS

mp A pointer to a mblk(9S) structure that contains a frame.

start The value or a pointer to it that contains the offset
from the L3 header, generally IP, of the first byte
that's covered by the checksum.

stuff The value or a pointer to it that contains the offset
from the L3 header of where the L4 checksum is. For
example, if using IPv4 and TCP, this would contain the
offset from the start of the IPv4 header to the first
byte of the TCP checksum.

end The value or a pointer to it that contains the offset
from the L3 header, generally IP, of the last byte that's
covered by the checksum.

value The value or a pointer to it that contains the actual
value of the checksum.

flags A series of one or more flags that have bitwise inclusive
ORed together. The set of flags have different meanings
depending on whether mp is being transmitted or received.

DESCRIPTION

The mac_hcksum_get() and mac_hcksum_set() functions are provided to
device drivers to get and set checksum related information. When a
device driver indicates that it supports the MAC_CAPAB_HCKSUM
capability as part of its mc_getcapab(9E) entry point, then it is
responsible for calling these functions appropriately during the
transmit and receive paths.

While both functions operate on an mblk_t, this function should only be
called on the first mblk_t that begins a given individual frame in a
chain. In other words, it only works on entries where it is the first
of many possible entries linked together by the b_cont member. The
first mblk_t received from any mac(9E) API or pointed to by a b_next
pointer should be used.

Receiving Data

When a device driver is receiving data, it is its responsibility to set
checksum information when it has indicated that it supports the
MAC_CAPAB_HCKSUM capability. Device drivers will call the
mac_hcksum_set() function to indicate what checksum information has
occurred.

The proper values to set depend on the flags passed in. The following
flags are supported when receiving data, note that they may have
different meanings from when transmitting data. The driver should set
the flags argument to the bitwise inclusive OR of the following values:

HCK_IPV4_HDRCKSUM_OK
This flag indicates that the hardware has verified the IPv4
header is correct and that the networking stack does not need
to verify it.

HCK_PARTIALCKSUM
This flag indicates that the hardware has computed a partial
checksum. When this flag is set, the driver is responsible for
passing in the partial checksum in the value argument as well
as the start and ending bytes of the checksum in the start and
end arguments.

HCK_FULLCKSUM
This flag indicates that the hardware has calculated the full
L4 header checksum; however, it wants the system to verify it.
The checksum should be passed in the value argument.

HCK_FULLCKSUM_OK
This flag indicates that the hardware has calculated the full
L4 header checksum and verified that it is correct. The
networking stack does not need to verify it.

The HCK_PARTIALCKSUM, HCK_FULLCKSUM, and HCK_FULLCKSUM_OK flags are all
mutually exclusive. A device driver should only set one of the three
flags.

If one of the arguments is not required based on the specified value of
flags, then the device driver should set any remaining arguments to 0.

Transmitting Data

When a device driver is transmitting data and it has advertised that it
supports the MAC_CAPAB_HCKSUM capability, then it must call the
mac_hcksum_get() function to determine what hardware checksumming
options are required to be performed by the hardware. While the device
driver may need the other fields, it must check the flags argument to
determine what it is being requested to do. The following values may
be set in flags:

HCK_IPV4_HDRCKSUM
The device driver must compute the IPv4 header checksum. No
other fields have been filled in.

HCK_PARTIALCKSUM
The device driver needs to compute the partial ones' complement
of the checksum. The system has filled in the start, stuff,
and end arguments to assist the device driver.

HCK_FULLCKSUM
The device driver should compute the full L4 checksum. No
other fields have been filled in for the device driver.

The flags that the device driver will get will depend on what the
device driver has advertised that it supports in response to the
mc_getcapab(9E) query for the MAC_CAPAB_HCKSUM capability.

The HCK_PARTIALCKSUM and HCK_FULLCKSUM flags are mutually exclusive.

CONTEXT

The mac_hcksum_get() and mac_hcksum_set() functions may be called from
any context.