On Fri, 11 Jul 2008, Eric W. Biederman wrote: > I just realized with a little care the block layer does have support for this, > or something very close. > > You setup a software raid mirror with one disk device. The physical > device can come in and out while the filesystems depend on the real device. Do you mean "the filesystems depend on the logical RAID device"? What's to prevent userspace from accessing the physical device directly? What this amounts to, in the end, is having a way to distinguish the set of I/O requests coming from the hibernation code (reading or writing the memory image) from the set of all other I/O requests. The driver or the block layer has to be set up to allow the first set through while blocking the second set. (And don't forget about the complications caused by error-recovery I/O during the hibernation activity!) Forcing the second set of requests to filter through an extra software layer is a clumsy way of accomplishing this. There ought to be a better approach. Alan Stern
