summaryrefslogtreecommitdiffhomepage
path: root/pkg/tcpip/stack
AgeCommit message (Collapse)Author
2020-01-14Changes TCP packet dispatch to use a pool of goroutines.Bhasker Hariharan
All inbound segments for connections in ESTABLISHED state are delivered to the endpoint's queue but for every segment delivered we also queue the endpoint for processing to a selected processor. This ensures that when there are a large number of connections in ESTABLISHED state the inbound packets are all handled by a small number of goroutines and significantly reduces the amount of work the goscheduler has to perform. We let connections in other states follow the current path where the endpoint's goroutine directly handles the segments. Updates #231 PiperOrigin-RevId: 289728325
2020-01-14Implement {g,s}etsockopt(IP_RECVTOS) for UDP socketsTamir Duberstein
PiperOrigin-RevId: 289718534
2020-01-13Do Source Address Selection when choosing an IPv6 source addressGhanan Gowripalan
Do Source Address Selection when choosing an IPv6 source address as per RFC 6724 section 5 rules 1-3: 1) Prefer same address 2) Prefer appropriate scope 3) Avoid deprecated addresses. A later change will update Source Address Selection to follow rules 4-8. Tests: Rule 1 & 2: stack.TestIPv6SourceAddressSelectionScopeAndSameAddress, Rule 3: stack.TestAutoGenAddrTimerDeprecation, stack.TestAutoGenAddrDeprecateFromPI PiperOrigin-RevId: 289559373
2020-01-13Allow dual stack sockets to operate on AF_INETTamir Duberstein
Fixes #1490 Fixes #1495 PiperOrigin-RevId: 289523250
2020-01-10Automated rollback of changelist 288990597Ghanan Gowripalan
PiperOrigin-RevId: 289169518
2020-01-09New sync package.Ian Gudger
* Rename syncutil to sync. * Add aliases to sync types. * Replace existing usage of standard library sync package. This will make it easier to swap out synchronization primitives. For example, this will allow us to use primitives from github.com/sasha-s/go-deadlock to check for lock ordering violations. Updates #1472 PiperOrigin-RevId: 289033387
2020-01-09Inform NDPDispatcher when Stack learns about available configurations via DHCPv6Ghanan Gowripalan
Inform the Stack's NDPDispatcher when it receives an NDP Router Advertisement that updates the available configurations via DHCPv6. The Stack makes sure that its NDPDispatcher isn't informed unless the avaiable configurations via DHCPv6 for a NIC is updated. Tests: Test that a Stack's NDPDispatcher is informed when it receives an NDP Router Advertisement that informs it of new configurations available via DHCPv6. PiperOrigin-RevId: 289001283
2020-01-09Separate NDP tests into its own packageGhanan Gowripalan
Internal tools timeout after 60s during tests that are required to pass before changes can be submitted. Separate out NDP tests into its own package to help prevent timeouts when testing. PiperOrigin-RevId: 288990597
2020-01-09Change BindToDeviceOption to store NICIDEyal Soha
This makes it possible to call the sockopt from go even when the NIC has no name. PiperOrigin-RevId: 288955236
2020-01-09Allow clients to store an opaque NICContext with NICsBert Muthalaly
...retrievable later via stack.NICInfo(). Clients of this library can use it to add metadata that should be tracked alongside a NIC, to avoid having to keep a map[tcpip.NICID]metadata mirroring stack.Stack's nic map. PiperOrigin-RevId: 288924900
2020-01-08CancellableTimer to encapsulate the work of safely stopping timersGhanan Gowripalan
Add a new CancellableTimer type to encapsulate the work of safely stopping timers when it fires at the same time some "related work" is being handled. The term "related work" is some work that needs to be done while having obtained some common lock (L). Example: Say we have an invalidation timer that may be extended or cancelled by some event. Creating a normal timer and simply cancelling may not be sufficient as the timer may have already fired when the event handler attemps to cancel it. Even if the timer and event handler obtains L before doing work, once the event handler releases L, the timer will eventually obtain L and do some unwanted work. To prevent the timer from doing unwanted work, it checks if it should early return instead of doing the normal work after obtaining L. When stopping the timer callers must have L locked so the timer can be safely informed that it should early return. Test: Tests that CancellableTimer fires and resets properly. Test to make sure the timer fn is not called after being stopped within the lock L. PiperOrigin-RevId: 288806984
2020-01-08Introduce tcpip.SockOptBoolTamir Duberstein
...and port V6OnlyOption to it. PiperOrigin-RevId: 288789451
2020-01-08Combine various Create*NIC methods into CreateNICWithOptions.Bert Muthalaly
PiperOrigin-RevId: 288779416
2020-01-08Rename tcpip.SockOpt{,Int}Tamir Duberstein
PiperOrigin-RevId: 288772878
2020-01-08Remove redundant function argumentTamir Duberstein
PacketLooping is already a member on the passed Route. PiperOrigin-RevId: 288721500
2020-01-08Add NIC.isLoopback()Bert Muthalaly
...enabling us to remove the "CreateNamedLoopbackNIC" variant of CreateNIC and all the plumbing to connect it through to where the value is read in FindRoute. PiperOrigin-RevId: 288713093
2020-01-07Support deprecating SLAAC addresses after the preferred lifetimeGhanan Gowripalan
Support deprecating network endpoints on a NIC. If an endpoint is deprecated, it should not be used for new connections unless a more preferred endpoint is not available, or unless the deprecated endpoint was explicitly requested. Test: Test that deprecated endpoints are only returned when more preferred endpoints are not available and SLAAC addresses are deprecated after its preferred lifetime PiperOrigin-RevId: 288562705
2020-01-07Disable auto-generation of IPv6 link-local addresses for loopback NICsGhanan Gowripalan
Test: Test that an IPv6 link-local address is not auto-generated for loopback NICs, even when it is enabled for non-loopback NICS. PiperOrigin-RevId: 288519591
2020-01-06Pass the NIC-internal name to the NIC name function when generating opaque IIDsGhanan Gowripalan
Pass the NIC-internal name to the NIC name function when generating opaque IIDs so implementations can use the name that was provided when the NIC was created. Previously, explicit NICID to NIC name resolution was required from the netstack integrator. Tests: Test that the name provided when creating a NIC is passed to the NIC name function when generating opaque IIDs. PiperOrigin-RevId: 288395359
2020-01-03Use opaque interface identifiers when generating IPv6 addresses via SLAACGhanan Gowripalan
Support using opaque interface identifiers when generating IPv6 addresses via SLAAC when configured to do so. Note, this change does not handle retries in response to DAD conflicts yet. That will also come in a later change. Test: Test that when SLAAC addresses are generated, they use opaque interface identifiers when configured to do so. PiperOrigin-RevId: 288078605
2020-01-03Support generating opaque interface identifiers as defined by RFC 7217Ghanan Gowripalan
Support generating opaque interface identifiers as defined by RFC 7217 for auto-generated IPv6 link-local addresses. Opaque interface identifiers will also be used for IPv6 addresses auto-generated via SLAAC in a later change. Note, this change does not handle retries in response to DAD conflicts yet. That will also come in a later change. Tests: Test that when configured to generated opaque IIDs, they are properly generated as outlined by RFC 7217. PiperOrigin-RevId: 288035349
2019-12-26Automated rollback of changelist 287029703gVisor bot
PiperOrigin-RevId: 287217899
2019-12-24Enable IP_RECVTOS socket option for datagram socketsRyan Heacock
Added the ability to get/set the IP_RECVTOS socket option on UDP endpoints. If enabled, TOS from the incoming Network Header passed as ancillary data in the ControlMessages. Test: * Added unit test to udp_test.go that tests getting/setting as well as verifying that we receive expected TOS from incoming packet. * Added a syscall test PiperOrigin-RevId: 287029703
2019-12-23Clear any host-specific NDP state when becoming a routerGhanan Gowripalan
This change supports clearing all host-only NDP state when NICs become routers. All discovered routers, discovered on-link prefixes and auto-generated addresses will be invalidated when becoming a router. This is because normally, routers do not process Router Advertisements to discover routers or on-link prefixes, and do not do SLAAC. Tests: Unittest to make sure that all discovered routers, discovered prefixes and auto-generated addresses get invalidated when transitioning from a host to a router. PiperOrigin-RevId: 286902309
2019-12-18Allow 'out-of-line' routing table updates for Router and Prefix discovery eventsGhanan Gowripalan
This change removes the requirement that a new routing table be provided when a router or prefix discovery event happens so that an updated routing table may be provided to the stack at a later time from the event. This change is to address the use case where the netstack integrator may need to obtain a lock before providing updated routes in response to the events above. As an example, say we have an integrator that performs the below two operations operations as described: A. Normal route update: 1. Obtain integrator lock 2. Update routes in the integrator 3. Call Stack.SetRouteTable with the updated routes 3.1. Obtain Stack lock 3.2. Update routes in Stack 3.3. Release Stack lock 4. Release integrator lock B. NDP event triggered route update: 1. Obtain Stack lock 2. Call event handler 2.1. Obtain integrator lock 2.2. Update routes in the integrator 2.3. Release integrator lock 2.4. Return updated routes to update Stack 3. Update routes in Stack 4. Release Stack lock A deadlock may occur if a Normal route update was attemped at the same time an NDP event triggered route update was attempted. With threads T1 and T2: 1) T1 -> A.1, A.2 2) T2 -> B.1 3) T1 -> A.3 (hangs at A.3.1 since Stack lock is taken in step 2) 4) T2 -> B.2 (hangs at B.2.1 since integrator lock is taken in step 1) Test: Existing tests were modified to not provide or expect routing table changes in response to Router and Prefix discovery events. PiperOrigin-RevId: 286274712
2019-12-18Cleanup NDP TestsGhanan Gowripalan
This change makes sure that test variables are captured before running tests in parallel, and removes unneeded buffered channel allocations. This change also removes unnecessary timeouts. PiperOrigin-RevId: 286255066
2019-12-13Properly generate the EUI64 interface identifier from an Ethernet addressGhanan Gowripalan
Fixed a bug where the interface identifier was not properly generated from an Ethernet address. Tests: Unittests to make sure the functions generating the EUI64 interface identifier are correct. PiperOrigin-RevId: 285494562
2019-12-10Inform the integrator on receipt of an NDP Recursive DNS Server optionGhanan Gowripalan
This change adds support to let an integrator know when it receives an NDP Router Advertisement message with the NDP Recursive DNS Server option with at least one DNS server's address. The stack will not maintain any state related to the DNS servers - the integrator is expected to maintain any required state and invalidate the servers after its valid lifetime expires, or refresh the lifetime when a new one is received for a known DNS server. Test: Unittest to make sure that an event is sent to the integrator when an NDP Recursive DNS Server option is received with at least one address. PiperOrigin-RevId: 284890502
2019-12-06Do IPv6 Stateless Address Auto-Configuration (SLAAC)Ghanan Gowripalan
This change allows the netstack to do SLAAC as outlined by RFC 4862 section 5.5. Note, this change will not break existing uses of netstack as the default configuration for the stack options is set in such a way that SLAAC will not be performed. See `stack.Options` and `stack.NDPConfigurations` for more details. This change reuses 1 option and introduces a new one that is required to take advantage of SLAAC, all available under NDPConfigurations: - HandleRAs: Whether or not NDP RAs are processes - AutoGenGlobalAddresses: Whether or not SLAAC is performed. Also note, this change does not deprecate SLAAC generated addresses after the preferred lifetime. That will come in a later change (b/143713887). Currently, only the valid lifetime is honoured. Tests: Unittest to make sure that SLAAC generates and adds addresses only when configured to do so. Tests also makes sure that conflicts with static addresses do not modify the static address. PiperOrigin-RevId: 284265317
2019-12-05Add a type to represent the NDP Recursive DNS Server optionGhanan Gowripalan
This change adds a type to represent the NDP Recursive DNS Server option, as defined by RFC 8106 section 5.1. PiperOrigin-RevId: 284005493
2019-11-23Cleanup visibility.Adin Scannell
PiperOrigin-RevId: 282194656
2019-11-22Use PacketBuffers with GSO.Kevin Krakauer
PiperOrigin-RevId: 282045221
2019-11-14Use PacketBuffers for outgoing packets.Kevin Krakauer
PiperOrigin-RevId: 280455453
2019-11-12Do not handle TCP packets that include a non-unicast IP addressGhanan Gowripalan
This change drops TCP packets with a non-unicast IP address as the source or destination address as TCP is meant for communication between two endpoints. Test: Make sure that if the source or destination address contains a non-unicast address, no TCP packet is sent in response and the packet is dropped. PiperOrigin-RevId: 280073731
2019-11-12Discover on-link prefixes from Router Advertisements' Prefix Information optionsGhanan Gowripalan
This change allows the netstack to do NDP's Prefix Discovery as outlined by RFC 4861 section 6.3.4. If configured to do so, when a new on-link prefix is discovered, the routing table will be updated with a device route through the nic the RA arrived at. Likewise, when such a prefix gets invalidated, the device route will be removed. Note, this change will not break existing uses of netstack as the default configuration for the stack options is set in such a way that Prefix Discovery will not be performed. See `stack.Options` and `stack.NDPConfigurations` for more details. This change reuses 1 option and introduces a new one that is required to take advantage of Prefix Discovery, all available under NDPConfigurations: - HandleRAs: Whether or not NDP RAs are processes - DiscoverOnLinkPrefixes: Whether or not Prefix Discovery is performed (new) Another note: for a NIC to process Prefix Information options (in Router Advertisements), it must not be a router itself. Currently the netstack does not have per-interface routing configuration; the routing/forwarding configuration is controlled stack-wide. Therefore, if the stack is configured to enable forwarding/routing, no router Advertisements (and by extension the Prefix Information options) will be processed. Tests: Unittest to make sure that Prefix Discovery and updates to the routing table only occur if explicitly configured to do so. Unittest to make sure at max stack.MaxDiscoveredOnLinkPrefixes discovered on-link prefixes are remembered. PiperOrigin-RevId: 280049278
2019-11-07Add support for TIME_WAIT timeout.Bhasker Hariharan
This change adds explicit support for honoring the 2MSL timeout for sockets in TIME_WAIT state. It also adds support for the TCP_LINGER2 option that allows modification of the FIN_WAIT2 state timeout duration for a given socket. It also adds an option to modify the Stack wide TIME_WAIT timeout but this is only for testing. On Linux this is fixed at 60s. Further, we also now correctly process RST's in CLOSE_WAIT and close the socket similar to linux without moving it to error state. We also now handle SYN in ESTABLISHED state as per RFC5961#section-4.1. Earlier we would just drop these SYNs. Which can result in some tests that pass on linux to fail on gVisor. Netstack now honors TIME_WAIT correctly as well as handles the following cases correctly. - TCP RSTs in TIME_WAIT are ignored. - A duplicate TCP FIN during TIME_WAIT extends the TIME_WAIT and a dup ACK is sent in response to the FIN as the dup FIN indicates potential loss of the original final ACK. - An out of order segment during TIME_WAIT generates a dup ACK. - A new SYN w/ a sequence number > the highest sequence number in the previous connection closes the TIME_WAIT early and opens a new connection. Further to make the SYN case work correctly the ISN (Initial Sequence Number) generation for Netstack has been updated to be as per RFC. Its not a pure random number anymore and follows the recommendation in https://tools.ietf.org/html/rfc6528#page-3. The current hash used is not a cryptographically secure hash function. A separate change will update the hash function used to Siphash similar to what is used in Linux. PiperOrigin-RevId: 279106406
2019-11-06Rename nicid to nicID to follow go-readability initialismsGhanan Gowripalan
https://github.com/golang/go/wiki/CodeReviewComments#initialisms This change does not introduce any new functionality. It just renames variables from `nicid` to `nicID`. PiperOrigin-RevId: 278992966
2019-11-06Discover default routers from Router AdvertisementsGhanan Gowripalan
This change allows the netstack to do NDP's Router Discovery as outlined by RFC 4861 section 6.3.4. Note, this change will not break existing uses of netstack as the default configuration for the stack options is set in such a way that Router Discovery will not be performed. See `stack.Options` and `stack.NDPConfigurations` for more details. This change introduces 2 options required to take advantage of Router Discovery, all available under NDPConfigurations: - HandleRAs: Whether or not NDP RAs are processes - DiscoverDefaultRouters: Whether or not Router Discovery is performed Another note: for a NIC to process Router Advertisements, it must not be a router itself. Currently the netstack does not have per-interface routing configuration; the routing/forwarding configuration is controlled stack-wide. Therefore, if the stack is configured to enable forwarding/routing, no Router Advertisements will be processed. Tests: Unittest to make sure that Router Discovery and updates to the routing table only occur if explicitly configured to do so. Unittest to make sure at max stack.MaxDiscoveredDefaultRouters discovered default routers are remembered. PiperOrigin-RevId: 278965143
2019-11-06Use PacketBuffers, rather than VectorisedViews, in netstack.Kevin Krakauer
PacketBuffers are analogous to Linux's sk_buff. They hold all information about a packet, headers, and payload. This is important for: * iptables to access various headers of packets * Preventing the clutter of passing different net and link headers along with VectorisedViews to packet handling functions. This change only affects the incoming packet path, and a future change will change the outgoing path. Benchmark Regular PacketBufferPtr PacketBufferConcrete -------------------------------------------------------------------------------- BM_Recvmsg 400.715MB/s 373.676MB/s 396.276MB/s BM_Sendmsg 361.832MB/s 333.003MB/s 335.571MB/s BM_Recvfrom 453.336MB/s 393.321MB/s 381.650MB/s BM_Sendto 378.052MB/s 372.134MB/s 341.342MB/s BM_SendmsgTCP/0/1k 353.711MB/s 316.216MB/s 322.747MB/s BM_SendmsgTCP/0/2k 600.681MB/s 588.776MB/s 565.050MB/s BM_SendmsgTCP/0/4k 995.301MB/s 888.808MB/s 941.888MB/s BM_SendmsgTCP/0/8k 1.517GB/s 1.274GB/s 1.345GB/s BM_SendmsgTCP/0/16k 1.872GB/s 1.586GB/s 1.698GB/s BM_SendmsgTCP/0/32k 1.017GB/s 1.020GB/s 1.133GB/s BM_SendmsgTCP/0/64k 475.626MB/s 584.587MB/s 627.027MB/s BM_SendmsgTCP/0/128k 416.371MB/s 503.434MB/s 409.850MB/s BM_SendmsgTCP/0/256k 323.449MB/s 449.599MB/s 388.852MB/s BM_SendmsgTCP/0/512k 243.992MB/s 267.676MB/s 314.474MB/s BM_SendmsgTCP/0/1M 95.138MB/s 95.874MB/s 95.417MB/s BM_SendmsgTCP/0/2M 96.261MB/s 94.977MB/s 96.005MB/s BM_SendmsgTCP/0/4M 96.512MB/s 95.978MB/s 95.370MB/s BM_SendmsgTCP/0/8M 95.603MB/s 95.541MB/s 94.935MB/s BM_SendmsgTCP/0/16M 94.598MB/s 94.696MB/s 94.521MB/s BM_SendmsgTCP/0/32M 94.006MB/s 94.671MB/s 94.768MB/s BM_SendmsgTCP/0/64M 94.133MB/s 94.333MB/s 94.746MB/s BM_SendmsgTCP/0/128M 93.615MB/s 93.497MB/s 93.573MB/s BM_SendmsgTCP/0/256M 93.241MB/s 95.100MB/s 93.272MB/s BM_SendmsgTCP/1/1k 303.644MB/s 316.074MB/s 308.430MB/s BM_SendmsgTCP/1/2k 537.093MB/s 584.962MB/s 529.020MB/s BM_SendmsgTCP/1/4k 882.362MB/s 939.087MB/s 892.285MB/s BM_SendmsgTCP/1/8k 1.272GB/s 1.394GB/s 1.296GB/s BM_SendmsgTCP/1/16k 1.802GB/s 2.019GB/s 1.830GB/s BM_SendmsgTCP/1/32k 2.084GB/s 2.173GB/s 2.156GB/s BM_SendmsgTCP/1/64k 2.515GB/s 2.463GB/s 2.473GB/s BM_SendmsgTCP/1/128k 2.811GB/s 3.004GB/s 2.946GB/s BM_SendmsgTCP/1/256k 3.008GB/s 3.159GB/s 3.171GB/s BM_SendmsgTCP/1/512k 2.980GB/s 3.150GB/s 3.126GB/s BM_SendmsgTCP/1/1M 2.165GB/s 2.233GB/s 2.163GB/s BM_SendmsgTCP/1/2M 2.370GB/s 2.219GB/s 2.453GB/s BM_SendmsgTCP/1/4M 2.005GB/s 2.091GB/s 2.214GB/s BM_SendmsgTCP/1/8M 2.111GB/s 2.013GB/s 2.109GB/s BM_SendmsgTCP/1/16M 1.902GB/s 1.868GB/s 1.897GB/s BM_SendmsgTCP/1/32M 1.655GB/s 1.665GB/s 1.635GB/s BM_SendmsgTCP/1/64M 1.575GB/s 1.547GB/s 1.575GB/s BM_SendmsgTCP/1/128M 1.524GB/s 1.584GB/s 1.580GB/s BM_SendmsgTCP/1/256M 1.579GB/s 1.607GB/s 1.593GB/s PiperOrigin-RevId: 278940079
2019-11-06Validate incoming NDP Router Advertisements, as per RFC 4861 section 6.1.2Ghanan Gowripalan
This change validates incoming NDP Router Advertisements as per RFC 4861 section 6.1.2. It also includes the skeleton to handle Router Advertiements that arrive on some NIC. Tests: Unittest to make sure only valid NDP Router Advertisements are received/ not dropped. PiperOrigin-RevId: 278891972
2019-10-30Deep copy dispatcher views.Kevin Krakauer
When VectorisedViews were passed up the stack from packet_dispatchers, we were passing a sub-slice of the dispatcher's views fields. The dispatchers then immediately set those views to nil. This wasn't caught before because every implementer copied the data in these views before returning. PiperOrigin-RevId: 277615351
2019-10-30Store endpoints inside multiPortEndpoint in a sorted orderAndrei Vagin
It is required to guarantee the same order of endpoints after save/restore. PiperOrigin-RevId: 277598665
2019-10-29Add Close and Wait methods to stack.Ian Gudger
Link endpoints still don't have a unified way to be requested to stop. Updates #837 PiperOrigin-RevId: 277398952
2019-10-29Add endpoint tracking to the stack.Ian Gudger
In the future this will replace DanglingEndpoints. DanglingEndpoints must be kept for now due to issues with save/restore. This is arguably a cleaner design and allows the stack to know which transport endpoints might still be using its link endpoints. Updates #837 PiperOrigin-RevId: 277386633
2019-10-29Allow waiting for Endpoint worker goroutines to finish.Ian Gudger
Updates #837 PiperOrigin-RevId: 277325162
2019-10-28Use the user supplied TCP MSS when creating a new active socketGhanan Gowripalan
This change supports using a user supplied TCP MSS for new active TCP connections. Note, the user supplied MSS must be less than or equal to the maximum possible MSS for a TCP connection's route. If it is greater than the maximum possible MSS, the maximum possible MSS will be used as the connection's MSS instead. This change does not use this user supplied MSS for connections accepted from listening sockets - that will come in a later change. Test: Test that outgoing TCP SYN segments contain a TCP MSS option with the user supplied MSS if it is not greater than the maximum possible MSS for the route. PiperOrigin-RevId: 277185125
2019-10-24Use interface-specific NDP configurations instead of the stack-wide default.Ghanan Gowripalan
This change makes it so that NDP work is done using the per-interface NDP configurations instead of the stack-wide default NDP configurations to correctly implement RFC 4861 section 6.3.2 (note here, a host is a single NIC operating as a host device), and RFC 4862 section 5.1. Test: Test that we can set NDP configurations on a per-interface basis without affecting the configurations of other interfaces or the stack-wide default. Also make sure that after the configurations are updated, the updated configurations are used for NDP processes (e.g. Duplicate Address Detection). PiperOrigin-RevId: 276525661
2019-10-23Inform netstack integrator when Duplicate Address Detection completesGhanan Gowripalan
This change introduces a new interface, stack.NDPDispatcher. It can be implemented by the netstack integrator to receive NDP related events. As of this change, only DAD related events are supported. Tests: Existing tests were modified to use the NDPDispatcher's DAD events for DAD tests where it needed to wait for DAD completing (failing and resolving). PiperOrigin-RevId: 276338733
2019-10-22Respect new PrimaryEndpointBehavior when addresses gets promoted to permanentGhanan Gowripalan
This change makes sure that when an address which is already known by a NIC and has kind = permanentExpired gets promoted to permanent, the new PrimaryEndpointBehavior is respected. PiperOrigin-RevId: 276136317
2019-10-22netstack/tcp: software segmentation offloadAndrei Vagin
Right now, we send each tcp packet separately, we call one system call per-packet. This patch allows to generate multiple tcp packets and send them by sendmmsg. The arguable part of this CL is a way how to handle multiple headers. This CL adds the next field to the Prepandable buffer. Nginx test results: Server Software: nginx/1.15.9 Server Hostname: 10.138.0.2 Server Port: 8080 Document Path: /10m.txt Document Length: 10485760 bytes w/o gso: Concurrency Level: 5 Time taken for tests: 5.491 seconds Complete requests: 100 Failed requests: 0 Total transferred: 1048600200 bytes HTML transferred: 1048576000 bytes Requests per second: 18.21 [#/sec] (mean) Time per request: 274.525 [ms] (mean) Time per request: 54.905 [ms] (mean, across all concurrent requests) Transfer rate: 186508.03 [Kbytes/sec] received sw-gso: Concurrency Level: 5 Time taken for tests: 3.852 seconds Complete requests: 100 Failed requests: 0 Total transferred: 1048600200 bytes HTML transferred: 1048576000 bytes Requests per second: 25.96 [#/sec] (mean) Time per request: 192.576 [ms] (mean) Time per request: 38.515 [ms] (mean, across all concurrent requests) Transfer rate: 265874.92 [Kbytes/sec] received w/o gso: $ ./tcp_benchmark --client --duration 15 --ideal [SUM] 0.0-15.1 sec 2.20 GBytes 1.25 Gbits/sec software gso: $ tcp_benchmark --client --duration 15 --ideal --gso $((1<<16)) --swgso [SUM] 0.0-15.1 sec 3.99 GBytes 2.26 Gbits/sec PiperOrigin-RevId: 276112677