[Xen-devel] [PATCH 2/2] 4.1.2 blktap2 cleanup fixes.

["Dr. Greg Wettstein" <greg@xxxxxxxxxxxxxxxxx>]

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The following patch when applied on top of:

libxl: attempt to cleanup tapdisk processes on disk backend destroy.

Establishes correct cleanup behavior for blktap devices.  This patch
implements the release of the backend device before calling for
the destruction of the userspace component of the blktap device.

Without this patch the kernel xen-blkback driver deadlocks with
the blktap2 user control plane until the IPC channel is terminated by the
timeout on the select() call.  This results in a noticeable delay
in the termination of the guest and causes the blktap minor
number which had been allocated to be orphaned.

Signed-off-by: Greg Wettstein <greg@xxxxxxxxxxxx>

diff -r b184698e0893 tools/libxl/libxl_blktap2.c
--- a/tools/libxl/libxl_blktap2.c       Tue Nov 06 19:53:48 2012 -0600
+++ b/tools/libxl/libxl_blktap2.c       Tue Nov 06 19:54:23 2012 -0600
@@ -59,6 +59,7 @@ void libxl__device_destroy_tapdisk(libxl
     char *path, *params, *type, *disk;
     int err;
     tap_list_t tap;
+    libxl_ctx *ctx = libxl__gc_owner(gc);
 
     path = libxl__sprintf(gc, "%s/tapdisk-params", be_path);
     if (!path) return;
@@ -75,5 +76,11 @@ void libxl__device_destroy_tapdisk(libxl
     err = tap_ctl_find(type, disk, &tap);
     if (err < 0) return;
 
+    /*
+     * Remove the instance of the backend device to avoid a deadlock with the
+     * removal of the tap device.
+     */
+    xs_rm(ctx->xsh, XBT_NULL, be_path);
+
     tap_ctl_destroy(tap.id, tap.minor);
 }
diff -r b184698e0893 tools/libxl/libxl_device.c
--- a/tools/libxl/libxl_device.c        Tue Nov 06 19:53:48 2012 -0600
+++ b/tools/libxl/libxl_device.c        Tue Nov 06 19:54:23 2012 -0600
@@ -250,8 +250,7 @@ int libxl__device_destroy(libxl_ctx *ctx
     if (!state)
         goto out;
     if (atoi(state) != 4) {
-        libxl__device_destroy_tapdisk(&gc, be_path);
-        xs_rm(ctx->xsh, XBT_NULL, be_path);
+       libxl__device_destroy_tapdisk(&gc, be_path);
         goto out;
     }
 
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As always,
Dr. G.W. Wettstein, Ph.D.   Enjellic Systems Development, LLC.
4206 N. 19th Ave.           Specializing in information infra-structure
Fargo, ND  58102            development.
PH: 701-281-1686
FAX: 701-281-3949           EMAIL: greg@xxxxxxxxxxxx
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"Fungus doesn't take a vacation."
                                -- Rob Pike

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