From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Jackson <Ian.Jackson@eu.citrix.com>
Subject: Re: [PATCH v4 4/4] libxl: fix cd-eject
Date: Wed, 17 Feb 2016 12:15:59 +0000
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To: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org, Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Alex Braunegg <alex.braunegg@gmail.com>
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Roger Pau Monn=E9 writes ("Re: [PATCH v4 4/4] libxl: fix cd-eject"):
> Should we allow the PHY backend to handle empty files?
> (pdev_path =3D=3D NULL || pdev_path =3D=3D "").

Yes.  That is how it is supposed to work.

I think this was broken in in 97ee1f5d "libxl: add support for image
files for NetBSD" in 2011 (!) where this happened:

-        if (a->disk->format !=3D LIBXL_DISK_FORMAT_EMPTY &&
-            !S_ISBLK(a->stab.st_mode)) {
-            LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "Disk vdev=3D%s, backend phy"
-                       " unsuitable as phys path not a block device",
-                       a->disk->vdev);
-            return 0;
-        }
 =

-        return backend;
+        if (libxl__try_phy_backend(a->stab.st_mode))
+            return backend;

... [libxl_linux.c:] ...

+int libxl__try_phy_backend(mode_t st_mode)
+{
+    if (!S_ISBLK(st_mode)) {
+        return 0;
+    }
+
+    return 1;
+}

Note that the "a->disk->format !=3D LIBXL_DISK_FORMAT_EMPTY" clause has
been lost.

Ian.