Re: [Xen-devel] [PATCH] libxl: stat the path for all non-qdisk backends (including unknown)

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2013-04-26 at 15:17 +0100, Sylvain Munaut wrote:
> > Since the intention of that commit was to allow for qdisk backends with no
> > explicit file in dom0 (i.e. network remote backend such as ceph) the lowest
> > impact fix appears to be to make that explicit. This should probably be
> > revisited to rationalize the probing.
> 
> What about the remote disk case of blktap ?  blktap2.5 supports NBD
> already AFAIK
> and I'm pretty sure I'll hit that same stat issue soon for another
> remote blktap case.

Right, sounds like I should have gone with my first instinct which was:

8<------------------------------------------------------------

>From 884beff4a897d785f61705dcfa2f048536982d7c Mon Sep 17 00:00:00 2001
From: Ian Campbell <ian.campbell@xxxxxxxxxx>
Date: Fri, 26 Apr 2013 12:41:43 +0100
Subject: [PATCH] libxl: stat the path for all non-qdisk backends (including 
unknown)

The commit a8a1f236a296 "libxl: Only call stat() when adding a disk if we
expect a device to exist." changed things to only stat the file when the phy
backend was explicitly requested. This broke the case where we are probing and
would normally be able to decide on the phy option.

Since the intention of that commit was to allow for backends with no explicit
file in dom0 (i.e. network remote backend such as ceph) the lowest impact fix
appears to be to make that explicit. It turns out that tap disk can also
potentially handle such paths.

The only backend which requires a local file/device is PHY but we need to
handle UNKNOWN too in order for subsequent probing to work. Note that it is
not possible to autoprobe the backend if the path is not a local object, so we
don't need to worry about autoprobing ceph etc.

This should probably be revisited to rationalize the probing.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: dave.scott@xxxxxxxxxx
Cc: george.dunlap@xxxxxxxxxx
Cc: roger.pau@xxxxxxxxxx
Cc: ian.jackson@xxxxxxxxxx
---
 tools/libxl/libxl_device.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/tools/libxl/libxl_device.c b/tools/libxl/libxl_device.c
index eb60fd5..a826ece 100644
--- a/tools/libxl/libxl_device.c
+++ b/tools/libxl/libxl_device.c
@@ -236,7 +236,8 @@ int libxl__device_disk_set_backend(libxl__gc *gc, 
libxl_device_disk *disk) {
             return ERROR_INVAL;
         }
         memset(&a.stab, 0, sizeof(a.stab));
-    } else if (disk->backend == LIBXL_DISK_BACKEND_PHY &&
+    } else if ((disk->backend == LIBXL_DISK_BACKEND_UNKNOWN ||
+                disk->backend == LIBXL_DISK_BACKEND_PHY) &&
                disk->backend_domid == LIBXL_TOOLSTACK_DOMID &&
                !disk->script) {
         if (stat(disk->pdev_path, &a.stab)) {
-- 
1.7.2.5




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