On 5/13/25 18:29, Benjamin Marzinski wrote:
On Mon, May 12, 2025 at 11:49:19PM -0700, Christoph Hellwig wrote:
On Tue, May 13, 2025 at 08:32:12AM +0200, Hannes Reinecke wrote:
Reservations and stuff.
They should use the kernel persistent reservation API.
Currently QEMU isn't sending Persistent Reservation requests to
multipath devices at all. It's sending those directly to the underlying
scsi devices. The issue here is with all the other SCSI commands that
users want to send to their SCSI passthrough device that is actually a
multipath device on top of a number of SCSI paths. They expect to
get back the actual sense and status information, so QEMU needs to
send them via SG_IOs.
Without reading that sense and status information in kernel, the
multipath target can't know if it needs to fail a path and retry the
ioctl down a different path. QEMU can read this information, but it
doesn't know what path the multipath device send the ioctl down. This
patch just gives users a way to check the paths in the active pathgroup
(which all should be able to handle IO) and fail those that can't.
While QEMU is the driver of this, it's completely general functionality.
Ouch.
Different reservations on different paths? Really?
How do you manage to keep the reservations up-to-date?
My recommendation is to use the _same_ reservation on all paths,
precisely to avoid having to re-do reservations on path failure.
And for that scenario the kernel persistent reservation API
would work fine.
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
h...@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich
