to kproc_xxx as they actually make whole processes.
Thos makes way for us to add REAL kthread_create() and friends
that actually make theads. it turns out that most of these
calls actually end up being moved back to the thread version
when it's added. but we need to make this cosmetic change first.
I'd LOVE to do this rename in 7.0 so that we can eventually MFC the
new kthread_xxx() calls.
arrangement that has no intrinsic internal knowledge of whether devices
it is given are truly multipath devices. As such, this is a simplistic
approach, but still a useful one.
The basic approach is to (at present- this will change soon) use camcontrol
to find likely identical devices and and label the trailing sector of the
first one. This label contains both a full UUID and a name. The name is
what is presented in /dev/multipath, but the UUID is used as a true
distinguishor at g_taste time, thus making sure we don't have chaos
on a shared SAN where everyone names their data multipath as "Fred".
The first of N identical devices (and N *may* be 1!) becomes the active
path until a BIO request is failed with EIO or ENXIO. When this occurs,
the active disk is ripped away and the next in a list is picked to
(retry and) continue with.
During g_taste events new disks that meet the match criteria for existing
multipath geoms get added to the tail end of the list.
Thus, this active/passive setup actually does work for devices which
go away and come back, as do (now) mpt(4) and isp(4) SAN based disks.
There is still a lot to do to improve this- like about 5 of the 12
recommendations I've received about it, but it's been functional enough
for a while that it deserves a broader test base.
Reviewed by: pjd
Sponsored by: IronPort Systems
MFC: 2 months
