On Wed, Oct 28, 2026 at 06:10:56PM +0100, Kevin Wolf wrote: > The host_device block driver refuses to open a block device read-write > if the BLKROGET ioctl tells it that it's actually read-only. For such > devices it's possible to open a read-write file descriptor, but any > writes to the device would fail. > > There are valid use cases for which this check gets in the way, as > explained in the bug report: > > However, this behavior prevents a legitimate enterprise use case: > running VMs against storage replication target LUNs in a disaster > recovery configuration. Enterprise storage arrays (Dell Powermax, > Pure Storage) set the SCSI Write Protect bit on replication target > LUNs, causing the Linux kernel to mark them read-only via BLKROGET. > The VMs on the passive DR site need to start with these LUNs > attached - writes are expected to fail (the application middleware > knows it's on the passive side), and after a DR role swap the LUN > becomes writable and writes should succeed immediately without any > VM restart. > > In order to allow such use cases in which a currently read-only device > is deliberately opened read-write, add a new option to the host_device > driver that allows the user to skip the check. > > Buglink: https://redhat.atlassian.net/browse/RHEL-186136 > Signed-off-by: Kevin Wolf <[email protected]> > --- > qapi/block-core.json | 19 ++++++++++++++++++- > block/file-posix.c | 23 ++++++++++++++++++++--- > 2 files changed, 38 insertions(+), 4 deletions(-)
Reviewed-by: Eric Blake <[email protected]> -- Eric Blake, Principal Software Engineer Red Hat, Inc. Virtualization: qemu.org | libguestfs.org
