suggested ways of faking EIO?

Dan Nelson dnelson at
Fri Nov 23 23:07:01 PST 2007

In the last episode (Nov 23), Julian Elischer said:
> I need to make physio make a request from disk, and have the request
> come back asynchronously with an EIO. 
> I have tried just reading some distance past the end of a partition,
> but I'm not totally convinced that it acts exactly like as if I'd
> tried to read a bad sector. Since geom has been added, the legality
> of a read needs to be tested in the geometry layer, so I suppose it
> must come back asynchronously, as that is no longer directly executed
> through function calls but is it really the same as a disk failure?
> Anyone done this? or does anyone have a disk with a known bad sector
> I can try my test case on? :-)

The geom NOP module can fail a given percentage of I/O with whatever
error number you choose.  You could hack g_nop.c to make it fail on a
given sector instead.
	Dan Nelson
	dnelson at

More information about the freebsd-current mailing list