Add an option to gnop to allow rejecting I/O after allowing some through.

[chs]

Summary

Add a "count_until_fail" option to gnop, which says to start failing
I/O requests after the given number have been allowed though.

Test Plan

I've written a test that uses this feature to exercise FFS I/O error handling.

[rpokala]

lib/geom/nop/gnop.8

125 ↗

(On Diff #61910)

I/O requests

[kib]

sys/geom/nop/g_nop.c

198 ↗

(On Diff #61910)

if (sc->sc_count_until_fail != 0 && ...

[0mp]

lib/geom/nop/gnop.8

27 ↗

(On Diff #61910)

Remember to bump the date.

123 ↗

(On Diff #61910)

.Bl -tag -width "-r count_until_fail" is enough here. Macros are not expanded here anyway (the whole .Fl r Ar count_until_fail string is treated literally).

[mckusick]

With the minor changes requested, looks good to me.

[imp]

Modulo kib's quibble, this is ready to go. No need to repost the review if all you change is the .Dd date and kib's thing.