Siddharth Vadapalli says:

====================
J7200: CPSW5G: Add support for QSGMII mode to am65-cpsw driver

Add support for QSGMII mode to am65-cpsw driver.

Change log:

v4-> v5:
1. Move ti,j7200-cpswxg-nuss compatible to the line above the
   ti,j721e-cpsw-nuss compatible.
2. Add allOf and move if-then statements within it to allow future if-then
   statements to be added easily.

v3 -> v4:
1. Update bindings to disallow ports based on compatible, instead of
   adding a new if/then statement for the new compatible.
2. Add Else-If condition for RMII mode in the set of supported interfaces.
   Support for RMII mode is already present in the driver and I had
   missed out adding a condition for RMII mode in the previous patches.

v2 -> v3:
1. In ti,k3-am654-cpsw-nuss.yaml, restrict if/then statement to port
   nodes.

v1 -> v2:
1. Add new compatible for CPSW5G in ti,k3-am654-cpsw-nuss.yaml and extend
   properties for new compatible.
2. Add extra_modes member to struct am65_cpsw_pdata to be used for QSGMII
   mode by new compatible.
3. Add check for phylink supported modes to ensure that only one phy mode
   is advertised as supported.
4. Check if extra_modes supports QSGMII mode in am65_cpsw_nuss_mac_config()
   for register write.
5. Add check for assigning port->sgmii_base only when extra_modes is valid.

v4: https://lore.kernel.org/r/20220816060139.111934-1-s-vadapalli@ti.com/
v3: https://lore.kernel.org/r/20220606110443.30362-1-s-vadapalli@ti.com/
v2: https://lore.kernel.org/r/20220602114558.6204-1-s-vadapalli@ti.com/
v1: https://lore.kernel.org/r/20220531113058.23708-1-s-vadapalli@ti.com/
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

In TI's J7200 SoC CPSW5G ports, each of the 4 ports can be configured
as a QSGMII main or QSGMII-SUB port. This configuration is performed
by phy-gmii-sel driver on invoking the phy_set_mode_ext() function.

It is necessary for the QSGMII main port to be configured before any of
the QSGMII-SUB interfaces are brought up. Currently, the QSGMII-SUB
interfaces come up before the QSGMII main port is configured.

Fix this by moving the call to phy_set_mode_ext() from
am65_cpsw_nuss_ndo_slave_open() to am65_cpsw_nuss_init_slave_ports(),
thereby ensuring that the QSGMII main port is configured before any of
the QSGMII-SUB ports are brought up.
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

CPSW5G in J7200 supports additional modes like QSGMII and SGMII.
Add new compatible for J7200 and enable QSGMII mode in am65-cpsw driver.
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Update bindings for TI K3 J7200 SoC which contains 5 ports (4 external
ports) CPSW5G module and add compatible for it.

Changes made:
    - Add new compatible ti,j7200-cpswxg-nuss for CPSW5G.
    - Extend pattern properties for new compatible.
    - Change maximum number of CPSW ports to 4 for new compatible.
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

Sometimes, gcc will optimize the function by spliting it to two or
more functions. In this case, kfree_skb_reason() is splited to
kfree_skb_reason and kfree_skb_reason.part.0. However, the
function/tracepoint trace_kfree_skb() in it needs the return address
of kfree_skb_reason().

This split makes the call chains becomes:
  kfree_skb_reason() -> kfree_skb_reason.part.0 -> trace_kfree_skb()

which makes the return address that passed to trace_kfree_skb() be
kfree_skb().

Therefore, introduce '__fix_address', which is the combination of
'__noclone' and 'noinline', and apply it to kfree_skb_reason() to
prevent to from being splited or made inline.

(Is it better to simply apply '__noclone oninline' to kfree_skb_reason?
I'm thinking maybe other functions have the same problems)

Meanwhile, wrap 'skb_unref()' with 'unlikely()', as the compiler thinks
it is likely return true and splits kfree_skb_reason().
Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Wei Fang says:

====================
add interface mode select and RMII

From: Wei Fang <wei.fang@nxp.com>

The patches add the below feature support for both TJA1100 and
TJA1101 PHYs cards:
- Add MII and RMII mode support.
- Add REF_CLK input/output support for RMII mode.
====================

Link: https://lore.kernel.org/r/20220822015949.1569969-1-wei.fang@nxp.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Add below features support for both TJA1100 and TJA1101 cards:
- Add MII and RMII mode support.
- Add REF_CLK input/output support for RMII mode.
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

TJA110x REF_CLK can be configured as interface reference clock
intput or output when the RMII mode enabled. This patch add the
property to make the REF_CLK can be configurable.
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Petr Machata says:

====================
mlxsw: Introduce modular system support by minimal driver

Vadim Pasternak writes:

This patchset adds line cards support in mlxsw_minimal, which is used
for monitoring purposes on BMC systems. The BMC is connected to the
ASIC over I2C bus, unlike the host CPU that is connected to the ASIC
via PCI bus.

The BMC system needs to be notified whenever line cards become active
or inactive, so that, for example, netdevs will be registered /
unregistered by mlxsw_minimal. However, traps cannot be generated
towards the BMC over the I2C bus. To overcome that, the I2C bus driver
(i.e., mlxsw_i2c) registers an handler for an IRQ that is fired upon
specific system wide changes, like line card activation and
deactivation.

The generated event is handled by mlxsw_core, which checks whether
anything changed in the state of available line cards. If a line card
becomes active or inactive, interested parties such as mlxsw_minimal
are notified via their registered line card event callback.

Patch set overview:

Patches #1 is preparations.

Patches #2-#3 extend mlxsw_core with an infrastructure to handle the
	previously mentioned system events.

Patch #4 extends the I2C bus driver to register an handler for the IRQ
	fired upon specific system wide changes.

Patches #5-#8 gradually add line cards support in mlxsw_minimal by
	dynamically registering / unregistering netdevs for ports found on
	line cards, whenever a line card becomes active / inactive.
====================

Link: https://lore.kernel.org/r/cover.1661093502.git.petrm@nvidia.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Implement line card operation callbacks got_active() / got_inactive().
The purpose of these callback to create / remove line card ports after
line card is getting active / inactive.

Implement line ports_remove_selected() callback to support line card
un-provisioning flow through 'devlink'.

Add line card operation registration and de-registration APIs.

Add module offset for line card. Offset for main board iz zero.
For line card in slot #n offset is calculated as (#n - 1) multiplied by
maximum modules number.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

The interfaces for ports found on line card are created and removed
dynamically after line card is getting active or inactive.

Introduce per line card array with module to port mapping.
For each port get 'slot_index' through PMLP register and set port
mapping for the relevant [slot_index][module] entry.

Split module and port allocation into separate routines.

Split per line card port creation and removing into separate routines.
Motivation to re-use these routines for line card operations.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Perform ports allocation in a separate routine.
Motivation is to re-use this routine for ports found on line cards.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Add 'slot_index' field to port structure.
Replace zero slot_index argument with 'slot_index' in 'ethtool'
related APIs.
Add 'slot_index' argument to port initialization and
de-initialization related APIs.

Motivation is to prepare minimal driver for modular system support.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Extend i2c bus driver with interrupt handler to support system specific
hotplug events, related to line card state change.

Provide system IRQ line for interrupt handler. IRQ line Id could be
provided through the platform data if available, or could be set to the
default value.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Add line card system event handler. Register it with core. It is
triggered by system interrupts raised from chassis programmable logic
devices to CPU. The purpose is to handle line card state changes over
I2C bus.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

The purpose of system event handler is to handle system interrupts.
Such interrupts are raised to CPU from system programmable logic
devices, upon specific system wide changes, like line card activation
and deactivation.

The purpose is to create an alternative to trap mechanism, which
delivers these events to driver over PCI bus, but not available for
the driver working over I2C bus.

Mechanism is system dependent and applicable only for the systems
equipped with programmable devices with custom logic.

Add APIs for event handler registration and un-registration and API
which should be invoked from the registered callbacks when system
interrupt is raised to CPU.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Currently, each line card is initialized using the following steps:

1. Initializing its various fields (e.g., slot index).
2. Creating the corresponding devlink object.
3. Enabling events (i.e., traps) for changes in line card status.
4. Querying and processing line card status.

Unlike traps, the IRQ that notifies the CPU about line card status
changes cannot be enabled / disabled on a per line card basis.

If a handler is registered before the line cards are initialized, the
handler risks accessing uninitialized memory.

On the other hand, if the handler is registered after initialization,
we risk missing events. For example, in step 4, the driver might see
that a line card is in ready state and will tell the device to enable
it. When enablement is done, the line card will be activated and the
IRQ will be triggered. Since a handler was not registered, the event
will be missed.

Solve this by splitting the initialization sequence into two steps
(1-2 and 3-4). In a subsequent patch, the handler will be registered
between both steps.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Provide a bit of a brain dump of netlink related information
as documentation. Hopefully this will be useful to people
trying to navigate implementing YAML based parsing in languages
we won't be able to help with.

I started writing this doc while trying to figure out what
it'd take to widen the applicability of YAML to good old rtnl,
but the doc grew beyond that as it usually happens.

In all honesty a lot of this information is new to me as I usually
follow the "copy an existing example, drink to forget" process
of writing netlink user space, so reviews will be much appreciated.
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20220819200221.422801-2-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Subsequent patch will render the kdoc from
include/uapi/linux/netlink.h into Documentation.
We need to fix the warnings. While at it move
the comments on struct nlmsghdr to a proper
kdoc comment.

Link: https://lore.kernel.org/r/20220819200221.422801-1-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

In case ftmac100 is used with a DSA switch, Linux wants to set MTU
to 1504 to accommodate for DSA overhead. With the default max_mtu
it leads to the error message:
 ftmac100 92000000.mac eth0: error -22 setting MTU to 1504 to include DSA overhead

ftmac100 supports packet length 1518 (MAX_PKT_SIZE constant), so it is
safe to report it in max_mtu.
Signed-off-by: Sergei Antonov <saproj@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20220821160844.474277-1-saproj@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

Vladimir Oltean says:

====================
DSA changes for multiple CPU ports (part 3)

Those who have been following part 1:
https://patchwork.kernel.org/project/netdevbpf/cover/20220511095020.562461-1-vladimir.oltean@nxp.com/
and part 2:
https://patchwork.kernel.org/project/netdevbpf/cover/20220521213743.2735445-1-vladimir.oltean@nxp.com/
will know that I am trying to enable the second internal port pair from
the NXP LS1028A Felix switch for DSA-tagged traffic via "ocelot-8021q".
This series represents part 3 of that effort.

Covered here are some preparations in DSA for handling multiple DSA
masters:
- when changing the tagging protocol via sysfs
- when the masters go down
as well as preparation for monitoring the upper devices of a DSA master
(to support DSA masters under a LAG).

There are also 2 small preparations for the ocelot driver, for the case
where multiple tag_8021q CPU ports are used in a LAG. Both those changes
have to do with PGID forwarding domains.

Compared to v1, the patches were trimmed down to just another
preparation stage, and the UAPI changes were pushed further out to part 4.
https://patchwork.kernel.org/project/netdevbpf/cover/20220523104256.3556016-1-olteanv@gmail.com/

Compared to v2, I had to export a symbol I forgot to
(ocelot_port_teardown_dsa_8021q_cpu), to avoid a build breakage when the
felix and seville drivers are built as modules.
====================

Link: https://lore.kernel.org/r/20220819174820.3585002-1-vladimir.oltean@nxp.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

Currently when we have 2 CPU ports configured for DSA tag_8021q mode and
we put them in a LAG, a PGID dump looks like this:

PGID_SRC[0] = ports 4,
PGID_SRC[1] = ports 4,
PGID_SRC[2] = ports 4,
PGID_SRC[3] = ports 4,
PGID_SRC[4] = ports 0, 1, 2, 3, 4, 5,
PGID_SRC[5] = no ports

(ports 0-3 are user ports, ports 4 and 5 are CPU ports)

There are 2 problems with the configuration above:

- user ports should enable forwarding towards both CPU ports, not just 4,
  and the aggregation PGIDs should prune one CPU port or the other from
  the destination port mask, based on a hash computed from packet headers.

- CPU ports should not be allowed to forward towards themselves and also
  not towards other ports in the same LAG as themselves

The first problem requires fixing up the PGID_SRC of user ports, when
ocelot_port_assigned_dsa_8021q_cpu_mask() is called. We need to say that
when a user port is assigned to a tag_8021q CPU port and that port is in
a LAG, it should forward towards all ports in that LAG.

The second problem requires fixing up the PGID_SRC of port 4, to remove
ports 4 and 5 (in a LAG) from the allowed destinations.

After this change, the PGID source masks look as follows:

PGID_SRC[0] = ports 4, 5,
PGID_SRC[1] = ports 4, 5,
PGID_SRC[2] = ports 4, 5,
PGID_SRC[3] = ports 4, 5,
PGID_SRC[4] = ports 0, 1, 2, 3,
PGID_SRC[5] = no ports

Note that PGID_SRC[5] still looks weird (it should say "0, 1, 2, 3" just
like PGID_SRC[4] does), but I've tested forwarding through this CPU port
and it doesn't seem like anything is affected (it appears that PGID_SRC[4]
is being looked up on forwarding from the CPU, since both ports 4 and 5
have logical port ID 4). The reason why it looks weird is because
we've never called ocelot_port_assign_dsa_8021q_cpu() for any user port
towards port 5 (all user ports are assigned to port 4 which is in a LAG
with 5).

Since things aren't broken, I'm willing to leave it like that for now
and just document the oddity.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

This is a partial revert of commit c295f983 ("net: mscc: ocelot:
switch from {,un}set to {,un}assign for tag_8021q CPU ports"), because
as it turns out, this isn't how tag_8021q CPU ports under a LAG are
supposed to work.

Under that scenario, all user ports are "assigned" to the single
tag_8021q CPU port represented by the logical port corresponding to the
bonding interface. So one CPU port in a LAG would have is_dsa_8021q_cpu
set to true (the one whose physical port ID is equal to the logical port
ID), and the other one to false.

In turn, this makes 2 undesirable things happen:

(1) PGID_CPU contains only the first physical CPU port, rather than both
(2) only the first CPU port will be added to the private VLANs used by
    ocelot for VLAN-unaware bridging

To make the driver behave in the same way for both bonded CPU ports, we
need to bring back the old concept of setting up a port as a tag_8021q
CPU port, and this is what deals with VLAN membership and PGID_CPU
updating. But we also need the CPU port "assignment" (the user to CPU
port affinity), and this is what updates the PGID_SRC forwarding rules.

All DSA CPU ports are statically configured for tag_8021q mode when the
tagging protocol is changed to ocelot-8021q. User ports are "assigned"
to one CPU port or the other dynamically (this will be handled by a
future change).
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

More logic will be added to dsa_tree_setup_master() and
dsa_tree_teardown_master() in upcoming changes.

Reduce the indentation by one level in these functions by introducing
and using a dedicated iterator for CPU ports of a tree.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

The fact that the tagging protocol is set and queried from the
/sys/class/net/<dsa-master>/dsa/tagging file is a bit of a quirk from
the single CPU port days which isn't aging very well now that DSA can
have more than a single CPU port. This is because the tagging protocol
is a switch property, yet in the presence of multiple CPU ports it can
be queried and set from multiple sysfs files, all of which are handled
by the same implementation.

The current logic ensures that the net device whose sysfs file we're
changing the tagging protocol through must be down. That net device is
the DSA master, and this is fine for single DSA master / CPU port setups.

But exactly because the tagging protocol is per switch [ tree, in fact ]
and not per DSA master, this isn't fine any longer with multiple CPU
ports, and we must iterate through the tree and find all DSA masters,
and make sure that all of them are down.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

This is an adaptation of commit c0a8a9c2 ("net: dsa: automatically
bring user ports down when master goes down") for multiple DSA masters.
When a DSA master goes down, only the user ports under its control
should go down too, the others can still send/receive traffic.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

All the traffic to/from a DSA master is supposed to be distributed among
its DSA switch upper interfaces, so we should not allow other upper
device kinds.

An exception to this is DSA_TAG_PROTO_NONE (switches with no DSA tags),
and in that case it is actually expected to create e.g. VLAN interfaces
on the master. But for those, netdev_uses_dsa(master) returns false, so
the restriction doesn't apply.

The motivation for this change is to allow LAG interfaces of DSA masters
to be DSA masters themselves. We want to restrict the user's degrees of
freedom by 1: the LAG should already have all DSA masters as lowers, and
while lower ports of the LAG can be removed, none can be added after the
fact.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

When DSA gains support for multiple CPU ports in a LAG, it will become
mandatory to monitor the changeupper events for the DSA master.

In fact, there are already some restrictions to be imposed in that area,
namely that a DSA master cannot be a bridge port except in some special
circumstances.

Centralize the restrictions at the level of the DSA layer as a
preliminary step.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

dsa_slave_prechangeupper_sanity_check() is supposed to enforce some
adjacency restrictions, and calls ds->ops->port_prechangeupper if the
driver implements it.

We convert the error code from the port_prechangeupper() call to a
notifier code, and 0 is converted to NOTIFY_OK, but the caller of
dsa_slave_prechangeupper_sanity_check() stops at any notifier code
different from NOTIFY_DONE.

Avoid this by converting back the notifier code to an error code, so
that both NOTIFY_OK and NOTIFY_DONE will be seen as 0. This allows more
parallel sanity check functions to be added.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Traditionally, DSA has had a single netdev notifier handling function
for each device type.

For the sake of code cleanliness, we would like to introduce more
handling functions which do one thing, but the conditions for entering
these functions start to overlap. Example: a handling function which
tracks whether any bridges contain both DSA and non-DSA interfaces.
Either this is placed before dsa_slave_changeupper(), case in which it
will prevent that function from executing, or we place it after
dsa_slave_changeupper(), case in which we will prevent it from
executing. The other alternative is to ignore errors from the new
handling function (not ideal).

To support this usage, we need to change the pattern. In the new model,
we enter all notifier handling sub-functions, and exit with NOTIFY_DONE
if there is nothing to do. This allows the sub-functions to be
relatively free-form and independent from each other.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Arseniy Krasnov says:

====================
vsock: updates for SO_RCVLOWAT handling

This patchset includes some updates for SO_RCVLOWAT:

1) af_vsock:
   During my experiments with zerocopy receive, i found, that in some
   cases, poll() implementation violates POSIX: when socket has non-
   default SO_RCVLOWAT(e.g. not 1), poll() will always set POLLIN and
   POLLRDNORM bits in 'revents' even number of bytes available to read
   on socket is smaller than SO_RCVLOWAT value. In this case,user sees
   POLLIN flag and then tries to read data(for example using  'read()'
   call), but read call will be blocked, because  SO_RCVLOWAT logic is
   supported in dequeue loop in af_vsock.c. But the same time,  POSIX
   requires that:

   "POLLIN     Data other than high-priority data may be read without
               blocking.
    POLLRDNORM Normal data may be read without blocking."

   See https://www.open-std.org/jtc1/sc22/open/n4217.pdf, page 293.

   So, we have, that poll() syscall returns POLLIN, but read call will
   be blocked.

   Also in man page socket(7) i found that:

   "Since Linux 2.6.28, select(2), poll(2), and epoll(7) indicate a
   socket as readable only if at least SO_RCVLOWAT bytes are available."

   I checked TCP callback for poll()(net/ipv4/tcp.c, tcp_poll()), it
   uses SO_RCVLOWAT value to set POLLIN bit, also i've tested TCP with
   this case for TCP socket, it works as POSIX required.

   I've added some fixes to af_vsock.c and virtio_transport_common.c,
   test is also implemented.

2) virtio/vsock:
   It adds some optimization to wake ups, when new data arrived. Now,
   SO_RCVLOWAT is considered before wake up sleepers who wait new data.
   There is no sense, to kick waiter, when number of available bytes
   in socket's queue < SO_RCVLOWAT, because if we wake up reader in
   this case, it will wait for SO_RCVLOWAT data anyway during dequeue,
   or in poll() case, POLLIN/POLLRDNORM bits won't be set, so such
   exit from poll() will be "spurious". This logic is also used in TCP
   sockets.

3) vmci/vsock:
   Same as 2), but i'm not sure about this changes. Will be very good,
   to get comments from someone who knows this code.

4) Hyper-V:
   As Dexuan Cui mentioned, for Hyper-V transport it is difficult to
   support SO_RCVLOWAT, so he suggested to disable this feature for
   Hyper-V.
====================

Link: https://lore.kernel.org/r/de41de4c-0345-34d7-7c36-4345258b7ba8@sberdevices.ruSigned-off-by: Paolo Abeni <pabeni@redhat.com>

This adds test to check, that when poll() returns POLLIN, POLLRDNORM bits,
next read call won't block.
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

This adds extra condition to wake up data reader: do it only when number
of readable bytes >= SO_RCVLOWAT. Otherwise, there is no sense to kick
user, because it will wait until SO_RCVLOWAT bytes will be dequeued. This
check is performed in vsock_data_ready().
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Vishnu Dasa <vdasa@vmware.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

This adds extra condition to wake up data reader: do it only when number
of readable bytes >= SO_RCVLOWAT. Otherwise, there is no sense to kick
user,because it will wait until SO_RCVLOWAT bytes will be dequeued. This
check is performed in vsock_data_ready().
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

This adds 'vsock_data_ready()' which must be called by transport to kick
sleeping data readers. It checks for SO_RCVLOWAT value before waking
user, thus preventing spurious wake ups. Based on 'tcp_data_ready()' logic.
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Passing 1 as the target to notify_poll_in(), we don't honor
what the user has set via SO_RCVLOWAT, going to set POLLIN
and POLLRDNORM, even if we don't have the amount of bytes
expected by the user.

Let's use sock_rcvlowat() to get the right target to pass to
notify_poll_in();
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

This callback controls setting of POLLIN, POLLRDNORM output bits of poll()
syscall, but in some cases, it is incorrectly to set it, when socket has
at least 1 bytes of available data. Use 'target' which is already exists.
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Vishnu Dasa <vdasa@vmware.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

This callback controls setting of POLLIN, POLLRDNORM output bits of poll()
syscall, but in some cases, it is incorrectly to set it, when socket has
at least 1 bytes of available data. Use 'target' which is already exists.
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

For Hyper-V it is quiet difficult to support this socket option,due to
transport internals, so disable it.
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

This adds transport specific callback for SO_RCVLOWAT, because in some
transports it may be difficult to know current available number of bytes
ready to read. Thus, when SO_RCVLOWAT is set, transport may reject it.
Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>