From 0eb2baeb449d27d6e6208a257dba6be1aad4d476 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 16 Sep 2015 17:26:16 +0200 Subject: [PATCH] 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 Signed-off-by: Paolo Bonzini --- hw/scsi/scsi-generic.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/hw/scsi/scsi-generic.c b/hw/scsi/scsi-generic.c index 1b6350be41..a4626f72c1 100644 --- a/hw/scsi/scsi-generic.c +++ b/hw/scsi/scsi-generic.c @@ -210,6 +210,20 @@ static void scsi_read_complete(void * opaque, int ret) } 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); }