Re: [RFC-v2 3/6] vhost-scsi: add -vhost-scsi host device for use with tcm-vhost

On Sun, 2012-08-19 at 11:44 +0300, Michael S. Tsirkin wrote:

On Sat, Aug 18, 2012 at 05:36:26PM -0700, Nicholas A. Bellinger wrote:

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On Sat, 2012-08-18 at 22:12 +0300, Michael S. Tsirkin wrote:

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On Tue, Aug 14, 2012 at 01:31:14PM -0700, Nicholas A. Bellinger wrote:

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On Mon, 2012-08-13 at 11:53 +0300, Michael S. Tsirkin wrote:

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On Mon, Aug 13, 2012 at 08:35:14AM +0000, Nicholas A. Bellinger wrote:

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From: Stefan Hajnoczi <redacted>

<SNIP>

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Mmm, looking at how vhost_net_init + tap.c does this, but am not quite
what fd needs to be propagated up for virtio-scsi -> vhost-scsi..

Can you please elaborate on this one a bit more..?

The idea is to allow running as a user without access to
/dev/vhost-scsi.
For this, allow passing in the fd of /dev/vhost-scsi through unix domain sockets.

Ah, that is a pretty neat trick..   So for vhost-scsi code, this would
mean something along the lines of the following, yes..?

Yes but with one correction. See below.

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Thanks MST!

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diff --git a/hw/vhost-scsi.c b/hw/vhost-scsi.c
index 4206a75..8af8758 100644
--- a/hw/vhost-scsi.c
+++ b/hw/vhost-scsi.c

@@ -21,6 +21,7 @@ struct VHostSCSI {
     const char *id;
     const char *wwpn;
     uint16_t tpgt;
+    int vhostfd;
     struct vhost_dev dev;
     struct vhost_virtqueue vqs[VHOST_SCSI_VQ_NUM];
     QLIST_ENTRY(VHostSCSI) list;

@@ -114,13 +115,32 @@ void vhost_scsi_stop(VHostSCSI *vs, VirtIODevice *vdev)
 }
 
 static VHostSCSI *vhost_scsi_add(const char *id, const char *wwpn,
-                                 uint16_t tpgt)
+                                 uint16_t tpgt, const char *vhostfd_str)
 {
-    VHostSCSI *vs = g_malloc0(sizeof(*vs));
+    VHostSCSI *vs;
     int ret;
 
+    vs = g_malloc0(sizeof(*vs));
+    if (!vs) {
+        error_report("vhost-scsi: unable to allocate *vs\n");
+        return NULL;
+    }
+    vs->vhostfd = -1;
+
+    if (vhostfd_str) {
+        if (!qemu_isdigit(vhostfd_str[0])) {
+            error_report("vhost-scsi: passed vhostfd value is not a digit\n");
+            return NULL;

This let you use an fd which was open at exec
but does not allow for fd to be open later in
case device is hot-plugged.

See net_handle_fd_param - I think you can just rename it
qemu_handle_fd_param to avoid code duplication.

OK, so monitor_get_fd() will set this up for the case where the device
is hot-plugged.  That makes alot more sense now..

So renaming net_handle_fd_param -> qemu_handle_fd_param + moving into
cutils.c, and will include as a leading patch for RFC-v3.

Thanks MST!

--nab