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scsi-generic: let guests recognize readonly=on on passthrough devices

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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>
This commit is contained in:
Paolo Bonzini 2015-09-16 17:26:16 +02:00
parent 5e43efb29a
commit 0eb2baeb44
1 changed files with 14 additions and 0 deletions
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14
hw/scsi/scsi-generic.c
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@ -210,6 +210,20 @@ static void scsi_read_complete(void * opaque, int ret)
} }
blk_set_guest_block_size(s->conf.blk, s->blocksize); 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_data(&r->req, len);
scsi_req_unref(&r->req); scsi_req_unref(&r->req);
} }