Ido Schimmel says:

====================
nexthop: Small changes

This patch set contains a few small changes that I split out of the RFC
I sent last week [1]. Main change is the conversion of the nexthop
notification chain to a blocking chain so that it could be reused by
device drivers for nexthop objects programming in the future.

Tested with fib_nexthops.sh:

Tests passed: 164
Tests failed:   0

[1] https://lore.kernel.org/netdev/20200908091037.2709823-1-idosch@idosch.org/
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Commit c7cdbe2e ("vxlan: support for nexthop notifiers") registered
a listener in the VXLAN driver to the nexthop notification chain. Its
purpose is to cleanup FDB entries that use a nexthop that is being
deleted.

Test that such FDB entries are removed when the nexthop group that they
use is deleted. Test that entries are not deleted when a single nexthop
in the group is deleted.
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Currently, the in-kernel delete notification is emitted from the error
path of nexthop_add() and replace_nexthop(), which can be confusing to
in-kernel listeners as they are not familiar with the nexthop.

Instead, only emit the notification when the nexthop is actually
deleted. The following sub-cases are covered:

1. User space deletes the nexthop
2. The nexthop is deleted by the kernel due to a netdev event (e.g.,
   nexthop device going down)
3. A group is deleted because its last nexthop is being deleted
4. The network namespace of the nexthop device is deleted
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Currently, the only listener of the nexthop notification chain is the
VXLAN driver. Subsequent patches will add more listeners (e.g., device
drivers such as netdevsim) that need to be able to block when processing
notifications.

Therefore, convert the notification chain to a blocking one. This is
safe as notifications are always emitted from process context.
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Not used anywhere.
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Suggested-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Not used or implemented anywhere.
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

As CHELSIO_INLINE_CRYPTO is bool, and CHELSIO_T4 is tristate, the
dependency of CHELSIO_INLINE_CRYPTO on CHELSIO_T4 is not sufficient to
protect CRYPTO_DEV_CHELSIO_TLS and CHELSIO_IPSEC_INLINE.  The latter two
are also tristate, hence if CHELSIO_T4=n, they cannot be builtin, as
that would lead to link failures like:

    drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_main.c:259: undefined reference to `cxgb4_port_viid'

and

    drivers/net/ethernet/chelsio/inline_crypto/ch_ipsec/chcr_ipsec.c:752: undefined reference to `cxgb4_reclaim_completed_tx'

Fix this by re-adding dependencies on CHELSIO_T4 to tristate symbols.
The dependency of CHELSIO_INLINE_CRYPTO on CHELSIO_T4 is kept to avoid
asking the user.

Fixes: 6bd860ac ("chelsio/chtls: CHELSIO_INLINE_CRYPTO should depend on CHELSIO_T4")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

-trigger-test-event'

Ido Schimmel says:

====================
mlxsw: Introduce fw_fatal health reporter and test cmd to trigger test event

Jiri says:

This patch set introduces a health reporter for mlxsw that reports FW
fatal events. Alongside that, it introduces a test command that is used
to trigger a dummy FW fatal event by user:

$ sudo devlink health test pci/0000:03:00.0 reporter fw_fatal

$ devlink health
pci/0000:03:00.0:
  reporter fw_fatal
    state error error 1 recover 0 last_dump_date 2020-07-27 last_dump_time 16:33:27 auto_dump true

$ sudo devlink health dump show pci/0000:03:00.0 reporter fw_fatal -j -p
{
    "irisc_id": 0,
    "event": [
        "id": 3 ],
    "method": "query",
    "long_process": false,
    "command_type": "mad",
    "reg_attr_id": 0
}

As a dependency, the FW validation and flashing is moved to core.c.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Introduce devlink health reporter to report FW fatal events. Implement
the event listener using MFDE trap and enable the events to be
propagated using MFGD register configuration.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Introduce a test command for health reporters. User might use this
command to trigger test event on a reporter if the reporter supports it.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Introduce MFGD register that is used to configure firmware debugging.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Introduce MFDE register that is passed through MFDE trap in case of
fatal FW event.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

As the fw flashing code was moved to core.c, move the param which is
related to it there as well. Remove unnecessary parentheses on the way.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Extract the code calling params register/unregister driver ops into
separate functions. Call publish/unpublish unconditionally.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

As the firmware flashing is not specific to Spectrum, move the code to
core.c and avoid one op call and 2 exported symbols. Also, this allows
to do flash before call of driver->init function and possibly do other
core calls in between.

Do some small renaming here and there on the way to be consistent with
the rest of core.c code.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Among other changes, this version supports FW monitoring.
Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Wong Vee Khee says:

====================
net: stmmac: Add ethtool support for get|set channels

This patch set is to add support for user to get or set Tx/Rx channel
via ethtool. There are two patches that fixes bug introduced on upstream
in order to have the feature work.

Tested on Intel Tigerlake Platform.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

The current implementation of stmmac_stop_all_queues() and
stmmac_start_all_queues() will not work correctly when the value of
tx_queues_to_use is changed through ethtool -L DEVNAME rx N tx M command.

Also, netif_tx_start|stop_all_queues() are only needed in driver open()
and close() only.

Fixes: c22a3f48 net: stmmac: adding multiple napi mechanism
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Voon Weifeng <weifeng.voon@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

netif_set_real_num_tx_queues() & netif_set_real_num_rx_queues() should be
used to inform network stack about the real Tx & Rx queue (active) number
in both stmmac_open() and stmmac_resume(), therefore, we move the code
from stmmac_dvr_probe() to stmmac_hw_setup().

Fixes: c02b7a91 net: stmmac: use netif_set_real_num_{rx,tx}_queues
Signed-off-by: Aashish Verma <aashishx.verma@intel.com>
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Restructure NAPI add and delete process so that we can call them
accordingly in open() and ethtool_set_channels() accordingly.

Introduced stmmac_reinit_queues() to handle the transition needed
for changing Rx & Tx channels accordingly.
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Jakub Kicinski says:

====================
ethtool: add pause frame stats

This is the first (small) series which exposes some stats via
the corresponding ethtool interface. Here (thanks to the
excitability of netlink) we expose pause frame stats via
the same interfaces as ethtool -a / -A.

In particular the following stats from the standard:
 - 30.3.4.2 aPAUSEMACCtrlFramesTransmitted
 - 30.3.4.3 aPAUSEMACCtrlFramesReceived

4 real drivers are converted, I believe we got confirmation
from maintainers that all exposed stats match the standard.

v3:
 - fix mlx5 build
 - adjust the init logic in patch 1
v2:
 - netdevsim: add missing static
 - bnxt: fix sparse warning
 - mlx5: address Saeed's comments
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Check if the pause stats are reported by HW by checking the bitmap.
Calculation is based on the order of strings in main_strings from
ethtool -S. Hopefully the semantics of these stats match the standard..
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Plumb through all the indirection and copy some code from
ethtool -S. The names of the group indicate that these are
the stats we are after (and Saeed confirms it).

v3:
 - fix build in mlx5_rep
v2:
 - drop the ethool helper and call stats directly
 - don't pass 0 as initialized to in buffer
 - use local buffer
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Report standard pause frame stats. They are already aggregated
in struct ixgbe_hw_stats.

The combination of the registers is suggested as equivalent to
PAUSEMACCtrlFramesTransmitted / PAUSEMACCtrlFramesReceived
by the Intel 82576EB datasheet, I could not find any information
in the HW actually supported by ixgbe.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

These stats are already reported in ethtool -S.
Michael confirms they are equivalent to standard stats.

v2: - fix sparse warning about endian by using the macro
    - use u64 for pointer type
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Make sure the empty nest is reported even without stats.
Make sure reporting only selected stats works fine.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Add minimal ethtool interface for testing ethtool pause stats.

v2: add missing static on nsim_ethtool_ops
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Tell people that there now is an interface for querying pause frames.
A little bit of restructuring is needed given this is a first source
of such statistics.
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Currently drivers have to report their pause frames statistics
via ethtool -S, and there is a wide variety of names used for
these statistics.

Add the two statistics defined in IEEE 802.3x to the standard
API. Create a new ethtool request header flag for including
statistics in the response to GET commands.

Always create the ETHTOOL_A_PAUSE_STATS nest in replies when
flag is set. Testing if driver declares the op is not a reliable
way of checking if any stats will actually be included and therefore
we don't want to give the impression that presence of
ETHTOOL_A_PAUSE_STATS indicates driver support.

Note that this patch does not include PFC counters, which may fit
better in dcbnl? But mostly I don't need them/have a setup to test
them so I haven't looked deeply into exposing them :)

v3:
 - add a helper for "uninitializing" stats, rather than a cryptic
   memset() (Andrew)
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Julian Wiedmann says:

====================
s390/qeth: updates 2020-09-10

subject to positive review by the bridge maintainers on patch 5,
please apply the following patch series to netdev's net-next tree.

Alexandra adds BR_LEARNING_SYNC support to qeth. In addition to the
main qeth changes (controlling the feature, and raising switchdev
events), this also needs
- Patch 1 and 2 for some s390/cio infrastructure improvements
  (acked by Heiko to go in via net-next), and
- Patch 5 to introduce a new switchdev_notifier_type, so that a driver
  can clear all previously learned entries from the bridge FDB in case
  things go out-of-sync later on.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/switchdev.txt and 'man bridge' indicate that the
learning_sync bridge attribute is used to control whether a given
device will sync MAC addresses learned on its device port to a master
bridge FDB, where they will show up as 'extern_learn offload'. So we map
qeth_l2_dev2br_an_set() to the learning_sync bridge link attribute.

Turning off learning_sync will flush all extern_learn entries from the
bridge fdb and all pending events from the card's work queue.

When the hardware interface goes offline with learning_sync on
(e.g. for HW recovery), all extern_learn entries will be flushed from the
bridge fdb and all pending events from the card's work queue. When the
interface goes online again, it will send new notifications for all then
valid MACs. learning_sync attribute can not be modified while interface is
offline. See
'commit e6e771b3 ("s390/qeth: detach netdevice while card is offline")'

An alternative implementation would be to always offload the 'learning'
attribute of a software bridge to the hardware interface attached to it
and thus implicitly enable fdb notification. This was not chosen for 2
reasons:
1) In our case the software bridge is NOT a representation of a hardware
switch. It is just connected to a smart NIC that is able to inform
about the addresses attached to it. It is not necessarily using source
MAC learning for this and other bridgeports can be attached to other
NICs with different properties.
2) We want a means to enable this notification explicitly. There may be
cases where a bridgeport is set to 'learning', but we do not want to
enable the notification.
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/switchdev.txt and 'man bridge' indicate that the
learning_sync bridge attribute is used to indicate whether a given
device will sync MAC addresses learned on its device port to a master
bridge FDB.

learning_sync attribute can not be read while interface is offline (down).
See
'commit e6e771b3 ("s390/qeth: detach netdevice while card is offline")'
We return EOPNOTSUPP and not EONODEV in this case, because EONOTSUPP is the
only rc that is tolerated by 'bridge -d link show'.
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

In case hardware sends more device-to-bridge-address-change notfications
than the qeth-l2 driver can handle, the hardware will send an overflow
event and then stop sending any events. It expects software to flush its
FDB and start over again. Re-enabling address-change-notification will
report all current addresses.

In order to re-enable address-change-notification this patch defines
the functions qeth_l2_dev2br_an_set() and qeth_l2_dev2br_an_set_cb
to enable or disable dev-to-bridge-address-notification.

A following patch will use the learning_sync bridgeport flag to trigger
enabling or disabling of address-change-notification, so we define
priv->brport_features to store the current setting. BRIDGE_INFO and
ADDR_INFO functionality are mutually exclusive, whereas ADDR_INFO and
qeth_l2_vnicc* can be used together.

Alternative implementations to handle buffer overflow:
Just re-enabling notification and adding all newly reported addresses
would cover any lost 'add' events, but not the lost 'delete' events.
Then these invalid addresses would stay in the bridge FDB as long as the
device exists.
Setting the net device down and up, would be an alternative, but is a bit
drastic. If the net device has many secondary addresses this will create
many delete/add events at its peers which could de-stabilize the
network segment.
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

so the switchdev can notifiy the bridge to flush non-permanent fdb entries
for this port. This is useful whenever the hardware fdb of the switchdev
is reset, but the netdev and the bridgeport are not deleted.

Note that this has the same effect as the IFLA_BRPORT_FLUSH attribute.

CC: Jiri Pirko <jiri@resnulli.us>
CC: Ivan Vecera <ivecera@redhat.com>
CC: Roopa Prabhu <roopa@nvidia.com>
CC: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Acked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Acked-by: Ivan Vecera <ivecera@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

A qeth-l2 HiperSockets card can show switch-ish behaviour in the sense,
that it can report all MACs that are reachable via this interface. Just
like a switch device, it can notify the software bridge about changes
to its fdb. This patch exploits this device-to-bridge-notification and
extracts the relevant information from the hardware events to generate
notifications to an attached software bridge.

There are 2 sources for this information:
1) The reply message of Perform-Network-Subchannel-Operations (PNSO)
(operation code ADDR_INFO) reports all addresses that are currently
reachable (implemented in a later patch).
2) As long as device-to-bridge-notification is enabled, hardware will
generate address change notification events, whenever the content of
the hardware fdb changes (this patch).

The bridge_hostnotify feature (PNSO operation code BRIDGE_INFO) uses
the same address change notification events. We need to distinguish
between qeth_pnso_mode QETH_PNSO_BRIDGEPORT and QETH_PNSO_ADDR_INFO
and call a different handler. In both cases deadlocks must be
prevented, if the workqueue is drained under lock and QETH_PNSO_NONE,
when notification is disabled.

bridge_hostnotify generates udev events, there is no intend to do the same
for dev2br. Instead this patch will generate SWITCHDEV_FDB_ADD_TO_BRIDGE
and SWITCHDEV_FDB_DEL_TO_BRIDGE notifications, that will cause the
software bridge to add (or delete) entries to its fdb as 'extern_learn
offload'.

Documentation/networking/switchdev.txt proposes to add
"depends NET_SWITCHDEV" to driver's Kconfig. This is not done here,
so even in absence of the NET_SWITCHDEV module, the QETH_L2 module will
still be built, but then the switchdev notifiers will have no effect.

No VLAN filtering is done on the entries and VLAN information is not
passed on to the bridge fdb entries. This could be added later.
For now VLAN interfaces can be defined on the upper bridge interface.

Multicast entries are not passed on to the bridge fdb.
This could be added later. For now mcast flooding can be used in the
bridge.

The card reports all MACs that are in its FDB, but we must not pass on
MACs that are registered for this interface.
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This patch detects whether device-to-bridge-notification, provided
by the Perform Network Subchannel Operation (PNSO) operation code
ADDR_INFO (OC3), is supported by this card. A following patch will
map this to the learning_sync bridgeport flag, so we store it in
priv->brport_hw_features in bridgeport flag format.

Only IQD cards provide PNSO.
There is a feature bit to indicate whether the machine provides OC3,
unfortunately it is not set on old machines.
So PNSO is called to find out. As this will disable notification
and is exclusive with bridgeport_notification, this must be done
during card initialisation before previous settings are restored.

PNSO functionality requires some configuration values that are added to
the qeth_card.info structure. Some helper functions are defined to fill
them out when the card is brought online and some other places are
adapted, that can also benefit from these fields.
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Add helper functions to expose Channel Subsystem ID (CSSID), MIF Image Id
(IID), Channel ID (CHID) and Channel Path ID (CHPID).
These values are required by the qeth driver's exploitation of network-
address-change-notifications to determine which entries belong to this
interface.

Store the Partition identifier in System log, as this may be used to map
a Linux view to a Hardware view for debugging purpose.
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Add support for operation code 3 (OC3) of the
Perform-Network-Subchannel-Operations (PNSO) function
of the Channel-Subsystem-Call (CHSC) instruction.

PNSO provides 2 operation codes:
OC0 - BRIDGE_INFO
OC3 - ADDR_INFO (new)

Extend the function calls to *pnso* to pass the OC and
add new response code 0108.

Support for OC3 is indicated by a flag in the css_general_characteristics.
Signed-off-by: Alexandra Winter <wintera@linux.ibm.com>
Reviewed-by: Julian Wiedmann <jwi@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Reviewed-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

For EPOLLET, applications must call sendmsg until they get EAGAIN.
Otherwise, there is no guarantee that EPOLLOUT is sent if there was
a failure upon memory allocation.

As a result on high-speed NICs, userspace observes multiple small
sendmsgs after a partial sendmsg until EAGAIN, since TCP can send
1-2 TSOs in between two sendmsg syscalls:

// One large partial send due to memory allocation failure.
sendmsg(20MB)   = 2MB
// Many small sends until EAGAIN.
sendmsg(18MB)   = 64KB
sendmsg(17.9MB) = 128KB
sendmsg(17.8MB) = 64KB
...
sendmsg(...)    = EAGAIN
// At this point, userspace can assume an EPOLLOUT.

To fix this, set the SOCK_NOSPACE on all partial sendmsg scenarios
to guarantee that we send EPOLLOUT after partial sendmsg.

After this commit userspace can assume that it will receive an EPOLLOUT
after the first partial sendmsg. This EPOLLOUT will benefit from
sk_stream_write_space() logic delaying the EPOLLOUT until significant
space is available in write queue.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

If there was any event available on the TCP socket, tcp_poll()
will be called to retrieve all the events.  In tcp_poll(), we call
sk_stream_is_writeable() which returns true as long as we are at least
one byte below notsent_lowat.  This will result in quite a few
spurious EPLLOUT and frequent tiny sendmsg() calls as a result.

Similar to sk_stream_write_space(), use __sk_stream_is_writeable
with a wake value of 1, so that we set EPOLLOUT only if half the
space is available for write.
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>