netmap: iflib: stop krings during interface reset

When different processes open separate subsets of the
available rings of a same netmap interface, a device
reset may be performed while one of the processes
is actively using some rings (e.g., caused by another
process executing a nmport_open()).
With this patch, such situation will cause the
active process to get a POLLERR, so that it can
have a chance to detect the situation.
We also guarantee that no process is running a txsync
or rxsync (ioctl or poll) while an iflib device reset
is in progress.

PR: 252453
MFC after: 1 week

(cherry picked from commit 1d238b07d5d4d9660ae0e08daede6da7e91c7853)

netmap: iflib: fix asserts in netmap_fl_refill()

When netmap_fl_refill() is called at initialization time (e.g.,
during netmap_iflib_register()), nic_i must be 0, since the
free list is reinitialized. At the end of the refill cycle, nic_i
must still be zero, because exactly N descriptors (N is the ring size)
are refilled.
This patch therefore fixes the assertions to check on nic_i rather
than on nm_i. The current netmap_reset() may in fact cause nm_i
to be != 0 while the device is resetting: this may happen when
multiple non-cooperating processes open different subsets of the
available netmap rings.

PR: 252518
MFC after: 1 week

(cherry picked from commit 3189ba61673af5bd3ed2ee9e33be92bc0b9995ba)

netmap: refactor netmap_reset

The netmap_reset() function is meant to be called by the driver
when they initialize (or re-initialize) a hardware ring.
However, since the introduction of support for opening (in
netmap mode) a subset of the available rings, netmap_reset()
may be called multiple times on actively used rings, causing
both kring and netmap ring to transition to an inconsistent
state.
This changes improves the situation by resetting all the
indices fields of the kring to 0, as expected after the
reinitialization of a hardware ring.

PR: 252518
MFC after: 1 week

(cherry picked from commit 7ba6ecf216fb15e8b147db268b91d9b82c5a0682)

netmap: iflib: enable/disable krings on any interface reinit

Since 1d238b07d5d4d9660ae0e0, krings are disabled before
a reinit cycle triggered by iflib_netmap_register.
However, this operation is actually necessary also for
any interface reinit triggered by other causes (i.e.,
ifconfig commands).
We achieve this goal by moving the krings enable/disable
operation inside iflib_stop() and iflib_init_locked().

Once here, this change also removes some redundant operations
from iflib_netmap_register(), that are already performed by
iflib_stop().

PR: 252453
MFC after: 1 week

(cherry picked from commit 3d65fd97e85ab807f3baa62aa979ae527914a3ea)

iflib: fix build failure in case DEV_NETMAP is not defined

This addresses the build failure introduced by
3d65fd97e85ab807f3baa62.

MFC with: 3d65fd97e85ab807f3baa62

(cherry picked from commit 8aa8484cbf06bb26ad87177fe4aebcaf1519f138)

netmap: restore hwofs and support it in iflib

Restore the hwofs functionality temporarily disabled by
7ba6ecf216fb15e8b147db2 to prevent issues with iflib.
This patch brings the necessary changes to iflib to
enable howfs to allow interface restarts without
disrupting netmap applications actively using its
rings.
After this change, it becomes possible for multiple
non-cooperating netmap applications to use non-overlapping
subsets of the available netmap rings without clashing
with each other.

PR: 252453
MFC after: 1 week

(cherry picked from commit 55f0ad5fdee1a779d6889481ba591a819081b9ca)