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.