scsi-generic: let guests recognize readonly=on on passthrough devices
Passed-through SCSI devices can be opened with the readonly=on option.
When this happens, Linux filters away write commands so that the guest
cannot overwrite the contents of the device.
However, the guest does not know that the device is read-only, and
accepts writes. The writes only fail later when the page cache is
flushed.
This patch modifies scsi-generic to modify the MODE SENSE data and
set the read-only bit in the device-specific parameters, so that
the guest OS treats the disk as write protected.
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c
index 1b6350b..a4626f7 100644
--- a/hw/scsi/scsi-generic.c
+++ b/hw/scsi/scsi-generic.c
@@ -210,6 +210,20 @@
}
blk_set_guest_block_size(s->conf.blk, s->blocksize);
+ /* Patch MODE SENSE device specific parameters if the BDS is opened
+ * readonly.
+ */
+ if ((s->type == TYPE_DISK || s->type == TYPE_TAPE) &&
+ blk_is_read_only(s->conf.blk) &&
+ (r->req.cmd.buf[0] == MODE_SENSE ||
+ r->req.cmd.buf[0] == MODE_SENSE_10) &&
+ (r->req.cmd.buf[1] & 0x8) == 0) {
+ if (r->req.cmd.buf[0] == MODE_SENSE) {
+ r->buf[2] |= 0x80;
+ } else {
+ r->buf[3] |= 0x80;
+ }
+ }
scsi_req_data(&r->req, len);
scsi_req_unref(&r->req);
}
