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.\" Copyright (c) 2017, Joyent, Inc.
.\" Copyright 2022 Oxide Computer Company
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.Dd July 2, 2022
.Dt MRI_POLL 9E
.Os
.Sh NAME
.Nm mri_poll
.Nd Poll a ring for received network data
.Sh SYNOPSIS
.In sys/mac_provider.h
.Ft mblk_t *
.Fo prefix_ring_poll
.Fa "void *driver"
.Fa "int poll_bytes"
.Fc
.Sh INTERFACE LEVEL
.Sy Uncommitted -
This interface is still evolving.
API and ABI stability is not guaranteed.
.Sh PARAMETERS
.Bl -tag -width Fa
.It Fa driver
A pointer to the ring's private data that was passed in via the
.Fa mri_driver
member of the
.Xr mac_ring_info 9S
structure as part of the
.Xr mr_rget 9E
entry point.
.It Fa poll_bytes
The maximum number of bytes that the driver should poll in a given call.
.El
.Sh DESCRIPTION
The
.Fn mri_poll
entry point is called by the MAC framework when it wishes to have the
driver check the ring specified by
.Fa driver
for available data.
.Pp
The device driver should perform the same logic that it would when it's
procesing an interrupt and as described in the
.Sx Receiving Data
section of
.Xr mac 9E .
The main difference is that instead of calling
.Xr mac_ring_rx 9E ,
it should instead return that data as a
.Vt mblk_t
chain.
Also, while an interrupt may map to more than one ring in some drivers,
the driver should only process the ring indicated by
.Fa driver .
The MAC framework can be polling some rings that are receiving a lot of
traffic while still relying on interrupts for others.
.Pp
Drivers should exercise caution with the locking between the polling,
interrupt disabling routines, and the interrupt handler.
This mutex is generally scoped to a receive ring and is used to
synchronize the act of transitioning between polling and handling
interrupts.
That means that in addition to the
.Fn mri_poll
entry point, the
.Xr mi_enable 9E
and
.Xr mi_disable 9E
entry points should synchronize on the same mutex when transitioning the
device.
This is the same mutex that would be used when processing this ring
during an interrupt handler, though that mutex should only be used while
processing a specific ring and not held for the duration of the entire
interrupt handler.
.Pp
The driver should limit the number of frames it collects based on the
size value present in the
.Fa poll_bytes
argument.
The driver should sum up the total size of each processed frame and
compare that running total to
.Fa poll_bytes .
If there are fewer frames than,
.Fa poll_bytes ,
the driver should not wait and can instead return right away.
Similarly, if the driver has iterated around its entire descriptor ring
and still does not have enough enough, it is OK to return early.
Importantly, the framework is
.Em not
asking the driver to block until it has
.Fa poll_bytes
available .
.Sh RETURN VALUES
Upon successful completion, the device driver should return a message
block chain of collected frames.
If no frames are available or it encountered an error while procesing
data, then it should return
.Dv NULL .
.Sh SEE ALSO
.Xr mac 9E ,
.Xr mac_capab_rings 9E ,
.Xr mac_ring_rx 9E ,
.Xr mi_disable 9E ,
.Xr mi_enable 9E ,
.Xr mr_rget 9E ,
.Xr mac_ring_info 9S