[Qemu-devel] [PATCH 06/10] ISCSI: force use of sg for SMC and SSC devices

[Paolo Bonzini <pbonzini@redhat.com>]

From: Ronnie Sahlberg <ronniesahlberg@gmail.com>

If the device we open is a SMC or SSC device, then force the use of sg. We
dont have any medium changer or tape emulation so only passthrough via
real sg or scsi-generic via iscsi would work anyway.

Forcing sg also makes qemu skip trying to read from the device to guess
the image format by reading from the device (find_image_format()).
SMC devices do not implement READ6/10/12/16 so it is not possible to
read from them (SSC have different CDBs).

With this patch I can successfully manage a SMC device wiht iscsi in
passthrough mode.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
[Added TYPE_TAPE handling - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 block/iscsi.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/block/iscsi.c b/block/iscsi.c
index 029739e..ac65277 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -1022,6 +1022,16 @@ static int iscsi_open(BlockDriverState *bs, const char *filename, int flags)
     if (iscsi_url != NULL) {
         iscsi_destroy_url(iscsi_url);
     }
+
+    /* Medium changer or tape. We dont have any emulation for this so this must
+     * be sg ioctl compatible. We force it to be sg, otherwise qemu will try
+     * to read from the device to guess the image format.
+     */
+    if (iscsilun->type == TYPE_MEDIUM_CHANGER ||
+        iscsilun->type == TYPE_TAPE) {
+        bs->sg = 1;
+    }
+
     return 0;
 
 failed:
-- 
1.7.10.2