[Info-vax] Filesystems on VMS, was: Re: Command Procedure Pipe output to a variable

[Stephen Hoffman]

On 2021-09-22 15:44:18 +0000, abrsvc said:

>> BTW, did you know that once you load a device driver into VMS, you 
>> can't even remove it unlike what you can do elsewhere ?
> 
> The above statement is not 100% true.  There are some drivers that can 
> be unloaded.   Granted these are few, but the mechanism is there, but 
> rarely used.

AFAIK, there's no supported means to remove an OpenVMS device driver.

It is possible to remove device units for template devices. But that 
does not remove the device driver.

And it was possible—though AFAIK now entirely unsupported—to code a 
device driver to tolerate re-loading with SYSGEN RELOAD. Usually.

There might once have been some UNLOAD hooks around.

AFAIK, there's no API to quiesce an OpenVMS driver and to allow the 
driver to complete or to cancel its pending I/O operations and to 
deallocate resources.

Semi-related alternatives from elsewhere:

Linux added no-reboot support for patching a while back. Search targets 
for different Linux distros include LivePatch, Kpatch, Ksplice, Kgraft, 
KernelCare.

kexec replaces the running kernel with a different kernel, a form of 
rebooting without a trip through the console.

Various hypervisors can fail over to a second hypervisor host 
dynamically, though it remains to be seen if that will work with 
OpenVMS on x86-64, or with clustered OpenVMS hosts on x86-64.



-- 
Pure Personal Opinion | HoffmanLabs LLC