[PATCH 0 of 7] libxl: refactor tap disk handling

[PATCH 0 of 7] libxl: refactor tap disk handling

[Ian Campbell]

I'm not personally convinced that support for blktap2 devices should
be conflated in libxl with the PV block backend support but given it's
there lets at least correct it.

In a blktap2 system there is no "tap" PV backend type. blktap2 exposes
a standard block device and this is passed to a guest using the
standard blkback "vbd" (sometimes called "phy") backend. Drop the
"tap" backend type and associated (libxl internal ) DEVICE_TAP
enumeration value.

Also try and clarify the paths which fallback from blktap2 to qdisk
when the former is not present. Falling through a switch statement is
a neat way of doing this in some cases, but I don't think this is one
of them.

[PATCH 1 of 7] libxl: remove impossible check for backend != DISK_BACKEND_QDISK

[Ian Campbell]

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1302167172 -3600
# Node ID 29af1669de3ab2e7d41078eb33a0dfa9b69f09bb
# Parent  bbb1ffd81018b0b7677c8b526de118d4501f6d39
libxl: remove impossible check for backend != DISK_BACKEND_QDISK

In this case we are already in the DISK_BACKEND_QDISK case of a switch
statement on the same variable.

It is possible that we fell through from the DISK_BACKEND_TAP case
(although I'm about to remove that in a subsequent patch), however in
that case we are explicitly falling back from blktap2 to qdisk so
DEVICE_QDISK is still the right answer.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r bbb1ffd81018 -r 29af1669de3a tools/libxl/libxl.c
--- a/tools/libxl/libxl.c	Thu Apr 07 09:56:46 2011 +0100
+++ b/tools/libxl/libxl.c	Thu Apr 07 10:06:12 2011 +0100
@@ -1016,12 +1016,7 @@ int libxl_device_disk_add(libxl_ctx *ctx
             flexarray_append(back, "params");
             flexarray_append(back, libxl__sprintf(&gc, "%s:%s",
                           libxl__device_disk_string_of_format(disk->format), disk->pdev_path));
-
-            if (libxl__blktap_enabled(&gc) && 
-                 disk->backend != DISK_BACKEND_QDISK)
-                device.backend_kind = DEVICE_TAP;
-            else
-                device.backend_kind = DEVICE_QDISK;
+            device.backend_kind = DEVICE_QDISK;
             break;
         default:
             LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "unrecognized disk backend type: %d\n", disk->backend);

[PATCH 2 of 7] libxl: make fallback from blktap2 to qdisk more explicit

[Ian Campbell]

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1302167195 -3600
# Node ID 76d363a113e5ee6111bc9e0eca5a314644ce6295
# Parent  29af1669de3ab2e7d41078eb33a0dfa9b69f09bb
libxl: make fallback from blktap2 to qdisk more explicit.

When blktap2 is not present we fallback to qdisk, instead of falling
through a switch statement instead make this explicit, with a comment,
prior to the switch statement.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r 29af1669de3a -r 76d363a113e5 tools/libxl/libxl.c
--- a/tools/libxl/libxl.c	Thu Apr 07 10:06:12 2011 +0100
+++ b/tools/libxl/libxl.c	Thu Apr 07 10:06:35 2011 +0100
@@ -979,6 +979,10 @@ int libxl_device_disk_add(libxl_ctx *ctx
     device.domid = domid;
     device.kind = DEVICE_VBD;
 
+    /* If blktap is not available then fallback to qdisk */
+    if (disk->backend == DISK_BACKEND_TAP && !libxl__blktap_enabled(&gc))
+        disk->backend = DISK_BACKEND_QDISK;
+
     switch (disk->backend) {
         case DISK_BACKEND_PHY: 
             libxl__device_physdisk_major_minor(disk->pdev_path, &major, &minor);
@@ -991,7 +995,7 @@ int libxl_device_disk_add(libxl_ctx *ctx
             device.backend_kind = DEVICE_VBD;
             break;
         case DISK_BACKEND_TAP:
-            if (libxl__blktap_enabled(&gc) && disk->format != DISK_FORMAT_EMPTY) {
+            if (disk->format != DISK_FORMAT_EMPTY) {
                 const char *dev = libxl__blktap_devpath(&gc,
                                                disk->pdev_path, disk->format);
                 if (!dev) {
@@ -1012,7 +1016,8 @@ int libxl_device_disk_add(libxl_ctx *ctx
 
                 break;
             }
-        case DISK_BACKEND_QDISK: 
+            break;
+        case DISK_BACKEND_QDISK:
             flexarray_append(back, "params");
             flexarray_append(back, libxl__sprintf(&gc, "%s:%s",
                           libxl__device_disk_string_of_format(disk->format), disk->pdev_path));

[PATCH 3 of 7] libxl: convert an empty tap disk into a qdisk

[Ian Campbell]

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1302167196 -3600
# Node ID f5418873be3d097cbb374009898ce9c74255e047
# Parent  76d363a113e5ee6111bc9e0eca5a314644ce6295
libxl: convert an empty tap disk into a qdisk

I'm not sure that empty disks which are is_cdrom are especially valid,
or that a cdrom can ever be handled by tapdisk anyway but try to do
something sane since it seems that xl's parse_disk_config() routine
could potentially generate such a configuration (although whether from
a valid input string or not I'm not sure).

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r 76d363a113e5 -r f5418873be3d tools/libxl/libxl.c
--- a/tools/libxl/libxl.c	Thu Apr 07 10:06:35 2011 +0100
+++ b/tools/libxl/libxl.c	Thu Apr 07 10:06:36 2011 +0100
@@ -983,6 +983,14 @@ int libxl_device_disk_add(libxl_ctx *ctx
     if (disk->backend == DISK_BACKEND_TAP && !libxl__blktap_enabled(&gc))
         disk->backend = DISK_BACKEND_QDISK;
 
+    /*
+     * blktap cannot handle empty disks (aka cdroms). Fall back to
+     * qdisk because qemu-xen creates the disk based on the xenstore
+     * entries.
+     */
+    if (disk->backend == DISK_BACKEND_TAP && disk->format == DISK_FORMAT_EMPTY)
+        disk->backend == DISK_BACKEND_QDISK;
+
     switch (disk->backend) {
         case DISK_BACKEND_PHY: 
             libxl__device_physdisk_major_minor(disk->pdev_path, &major, &minor);
@@ -995,7 +1003,7 @@ int libxl_device_disk_add(libxl_ctx *ctx
             device.backend_kind = DEVICE_VBD;
             break;
         case DISK_BACKEND_TAP:
-            if (disk->format != DISK_FORMAT_EMPTY) {
+            {
                 const char *dev = libxl__blktap_devpath(&gc,
                                                disk->pdev_path, disk->format);
                 if (!dev) {
@@ -1003,8 +1011,8 @@ int libxl_device_disk_add(libxl_ctx *ctx
                     goto out_free;
                 }
                 flexarray_append(back, "tapdisk-params");
-                flexarray_append(back, libxl__sprintf(&gc, "%s:%s", 
-                    libxl__device_disk_string_of_format(disk->format), 
+                flexarray_append(back, libxl__sprintf(&gc, "%s:%s",
+                    libxl__device_disk_string_of_format(disk->format),
                     disk->pdev_path));
                 flexarray_append(back, "params");
                 flexarray_append(back, libxl__strdup(&gc, dev));
@@ -1013,8 +1021,6 @@ int libxl_device_disk_add(libxl_ctx *ctx
                 flexarray_append(back, "physical-device");
                 flexarray_append(back, libxl__sprintf(&gc, "%x:%x", major, minor));
                 device.backend_kind = DEVICE_VBD;
-
-                break;
             }
             break;
         case DISK_BACKEND_QDISK:

[PATCH 4 of 7] libxl: only a CDROM type disk can be empty

[Ian Campbell]

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1302167211 -3600
# Node ID cbf6ec01faef6502845d8201a717edc9fa6fae52
# Parent  f5418873be3d097cbb374009898ce9c74255e047
libxl: only a CDROM type disk can be empty.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r f5418873be3d -r cbf6ec01faef tools/libxl/libxl.c
--- a/tools/libxl/libxl.c	Thu Apr 07 10:06:36 2011 +0100
+++ b/tools/libxl/libxl.c	Thu Apr 07 10:06:51 2011 +0100
@@ -908,8 +908,13 @@ static int validate_virtual_disk(libxl__
     struct stat stat_buf;
     char *delimiter;
 
-    if (disk->format == DISK_FORMAT_EMPTY)
-        return 0;
+    if (disk->format == DISK_FORMAT_EMPTY) {
+        if (disk->is_cdrom)
+            return 0;
+        LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Empty disk %s is not a CDROM device\n",
+                   disk->vdev);
+        return ERROR_INVAL;
+    }
 
     if (disk->format == DISK_FORMAT_RAW) {
         delimiter = strchr(file_name, ':');

[PATCH 5 of 7] libxl: refactor DISK_BACKEND_PHY handling in libxl_device_disk_add

[Ian Campbell]

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1302167211 -3600
# Node ID ec3b25b5aa8095c5fe070173af888f032f6c2c5e
# Parent  cbf6ec01faef6502845d8201a717edc9fa6fae52
libxl: refactor DISK_BACKEND_PHY handling in libxl_device_disk_add

A step on the path to sharing this code with the tail-end of the
DISK_BACKEND_TAP case.

I made the result of libxl__blktap_devpath non-const to achieve
this. The existing caller calls libxl__strdup on the result but since
the function is an internal one and the result is already garbage
collected I think this is unnecessary and we can just use the
non-const result directly.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r cbf6ec01faef -r ec3b25b5aa80 tools/libxl/libxl.c
--- a/tools/libxl/libxl.c	Thu Apr 07 10:06:51 2011 +0100
+++ b/tools/libxl/libxl.c	Thu Apr 07 10:06:51 2011 +0100
@@ -949,6 +949,7 @@ int libxl_device_disk_add(libxl_ctx *ctx
     libxl__gc gc = LIBXL_INIT_GC(ctx);
     flexarray_t *front;
     flexarray_t *back;
+    char *dev;
     char *backend_type;
     int devid;
     libxl__device device;
@@ -997,36 +998,39 @@ int libxl_device_disk_add(libxl_ctx *ctx
         disk->backend == DISK_BACKEND_QDISK;
 
     switch (disk->backend) {
-        case DISK_BACKEND_PHY: 
-            libxl__device_physdisk_major_minor(disk->pdev_path, &major, &minor);
+        case DISK_BACKEND_PHY:
+            dev = disk->pdev_path;
+
+            libxl__device_physdisk_major_minor(dev, &major, &minor);
             flexarray_append(back, "physical-device");
             flexarray_append(back, libxl__sprintf(&gc, "%x:%x", major, minor));
 
             flexarray_append(back, "params");
-            flexarray_append(back, disk->pdev_path);
+            flexarray_append(back, dev);
 
             device.backend_kind = DEVICE_VBD;
             break;
         case DISK_BACKEND_TAP:
-            {
-                const char *dev = libxl__blktap_devpath(&gc,
-                                               disk->pdev_path, disk->format);
-                if (!dev) {
-                    rc = ERROR_FAIL;
-                    goto out_free;
-                }
-                flexarray_append(back, "tapdisk-params");
-                flexarray_append(back, libxl__sprintf(&gc, "%s:%s",
-                    libxl__device_disk_string_of_format(disk->format),
-                    disk->pdev_path));
-                flexarray_append(back, "params");
-                flexarray_append(back, libxl__strdup(&gc, dev));
-                backend_type = "phy";
-                libxl__device_physdisk_major_minor(dev, &major, &minor);
-                flexarray_append(back, "physical-device");
-                flexarray_append(back, libxl__sprintf(&gc, "%x:%x", major, minor));
-                device.backend_kind = DEVICE_VBD;
+            dev = libxl__blktap_devpath(&gc, disk->pdev_path, disk->format);
+            if (!dev) {
+                rc = ERROR_FAIL;
+                goto out_free;
             }
+            flexarray_append(back, "tapdisk-params");
+            flexarray_append(back, libxl__sprintf(&gc, "%s:%s",
+                libxl__device_disk_string_of_format(disk->format),
+                disk->pdev_path));
+
+            flexarray_append(back, "params");
+            flexarray_append(back, dev);
+
+            backend_type = "phy";
+
+            libxl__device_physdisk_major_minor(dev, &major, &minor);
+            flexarray_append(back, "physical-device");
+            flexarray_append(back, libxl__sprintf(&gc, "%x:%x", major, minor));
+
+            device.backend_kind = DEVICE_VBD;
             break;
         case DISK_BACKEND_QDISK:
             flexarray_append(back, "params");
@@ -1110,7 +1114,7 @@ int libxl_device_disk_del(libxl_ctx *ctx
 char * libxl_device_disk_local_attach(libxl_ctx *ctx, libxl_device_disk *disk)
 {
     libxl__gc gc = LIBXL_INIT_GC(ctx);
-    const char *dev = NULL;
+    char *dev = NULL;
     char *ret = NULL;
 
     switch (disk->backend) {
diff -r cbf6ec01faef -r ec3b25b5aa80 tools/libxl/libxl_blktap2.c
--- a/tools/libxl/libxl_blktap2.c	Thu Apr 07 10:06:51 2011 +0100
+++ b/tools/libxl/libxl_blktap2.c	Thu Apr 07 10:06:51 2011 +0100
@@ -24,9 +24,9 @@ int libxl__blktap_enabled(libxl__gc *gc)
     return !tap_ctl_check(&msg);
 }
 
-const char *libxl__blktap_devpath(libxl__gc *gc,
-                                 const char *disk,
-                                 libxl_disk_format format)
+char *libxl__blktap_devpath(libxl__gc *gc,
+                            const char *disk,
+                            libxl_disk_format format)
 {
     const char *type;
     char *params, *devname = NULL;
diff -r cbf6ec01faef -r ec3b25b5aa80 tools/libxl/libxl_internal.h
--- a/tools/libxl/libxl_internal.h	Thu Apr 07 10:06:51 2011 +0100
+++ b/tools/libxl/libxl_internal.h	Thu Apr 07 10:06:51 2011 +0100
@@ -325,9 +325,9 @@ _hidden int libxl__blktap_enabled(libxl_
  *    returns device path xenstore wants to have. returns NULL
  *      if no device corresponds to the disk.
  */
-_hidden const char *libxl__blktap_devpath(libxl__gc *gc,
-                                 const char *disk,
-                                 libxl_disk_format format);
+_hidden char *libxl__blktap_devpath(libxl__gc *gc,
+                                    const char *disk,
+                                    libxl_disk_format format);
 
 _hidden char *libxl__uuid2string(libxl__gc *gc, const libxl_uuid uuid);
 
diff -r cbf6ec01faef -r ec3b25b5aa80 tools/libxl/libxl_noblktap2.c
--- a/tools/libxl/libxl_noblktap2.c	Thu Apr 07 10:06:51 2011 +0100
+++ b/tools/libxl/libxl_noblktap2.c	Thu Apr 07 10:06:51 2011 +0100
@@ -21,9 +21,9 @@ int libxl__blktap_enabled(libxl__gc *gc)
     return 0;
 }
 
-const char *libxl__blktap_devpath(libxl__gc *gc,
-                                 const char *disk,
-                                 libxl_disk_format format)
+char *libxl__blktap_devpath(libxl__gc *gc,
+                            const char *disk,
+                            libxl_disk_format format)
 {
     return NULL;
 }

[PATCH 6 of 7] libxl: handle the tail end of a tap device using the phy backend handling code

[Ian Campbell]

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1302167211 -3600
# Node ID 40b0954cb5d9bdd0b943963afb79914ba5cb08c9
# Parent  ec3b25b5aa8095c5fe070173af888f032f6c2c5e
libxl: handle the tail end of a tap device using the phy backend handling code

We are literally creating a phy backend on top of a blktap2 created
device anyway so we might as well reuse the code and make this
explicit.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r ec3b25b5aa80 -r 40b0954cb5d9 tools/libxl/libxl.c
--- a/tools/libxl/libxl.c	Thu Apr 07 10:06:51 2011 +0100
+++ b/tools/libxl/libxl.c	Thu Apr 07 10:06:51 2011 +0100
@@ -1000,7 +1000,7 @@ int libxl_device_disk_add(libxl_ctx *ctx
     switch (disk->backend) {
         case DISK_BACKEND_PHY:
             dev = disk->pdev_path;
-
+    do_backend_phy:
             libxl__device_physdisk_major_minor(dev, &major, &minor);
             flexarray_append(back, "physical-device");
             flexarray_append(back, libxl__sprintf(&gc, "%x:%x", major, minor));
@@ -1021,17 +1021,11 @@ int libxl_device_disk_add(libxl_ctx *ctx
                 libxl__device_disk_string_of_format(disk->format),
                 disk->pdev_path));
 
-            flexarray_append(back, "params");
-            flexarray_append(back, dev);
-
             backend_type = "phy";
 
-            libxl__device_physdisk_major_minor(dev, &major, &minor);
-            flexarray_append(back, "physical-device");
-            flexarray_append(back, libxl__sprintf(&gc, "%x:%x", major, minor));
-
-            device.backend_kind = DEVICE_VBD;
-            break;
+            /* now create a phy device to export the device to the guest */
+            goto do_backend_phy;
+
         case DISK_BACKEND_QDISK:
             flexarray_append(back, "params");
             flexarray_append(back, libxl__sprintf(&gc, "%s:%s",

[PATCH 7 of 7] libxl: Drop internal DEVICE_TAP backend type

[Ian Campbell]

# HG changeset patch
# User Ian Campbell <ian.campbell@citrix.com>
# Date 1302167211 -3600
# Node ID 6162ae4cc9a7fae505f6b081a6698ecdd94418c2
# Parent  40b0954cb5d9bdd0b943963afb79914ba5cb08c9
libxl: Drop internal DEVICE_TAP backend type

There is no such thing with blktap2, the backend in that case is PHY.

libxl_device_disk_del was just plain wrong in this regard, fix it to
select the appropriate backend_kind.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

diff -r 40b0954cb5d9 -r 6162ae4cc9a7 tools/libxl/libxl.c
--- a/tools/libxl/libxl.c	Thu Apr 07 10:06:51 2011 +0100
+++ b/tools/libxl/libxl.c	Thu Apr 07 10:06:51 2011 +0100
@@ -950,7 +950,6 @@ int libxl_device_disk_add(libxl_ctx *ctx
     flexarray_t *front;
     flexarray_t *back;
     char *dev;
-    char *backend_type;
     int devid;
     libxl__device device;
     int major, minor, rc;
@@ -970,7 +969,6 @@ int libxl_device_disk_add(libxl_ctx *ctx
         goto out_free;
     }
 
-    backend_type = libxl__device_disk_string_of_backend(disk->backend);
     devid = libxl__device_disk_dev_number(disk->vdev, NULL, NULL);
     if (devid==-1) {
         LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Invalid or unsupported"
@@ -1021,8 +1019,6 @@ int libxl_device_disk_add(libxl_ctx *ctx
                 libxl__device_disk_string_of_format(disk->format),
                 disk->pdev_path));
 
-            backend_type = "phy";
-
             /* now create a phy device to export the device to the guest */
             goto do_backend_phy;
 
@@ -1051,7 +1047,7 @@ int libxl_device_disk_add(libxl_ctx *ctx
     flexarray_append(back, "dev");
     flexarray_append(back, disk->vdev);
     flexarray_append(back, "type");
-    flexarray_append(back, backend_type);
+    flexarray_append(back, libxl__device_disk_string_of_backend(disk->backend));
     flexarray_append(back, "mode");
     flexarray_append(back, disk->readwrite ? "w" : "r");
 
@@ -1093,14 +1089,30 @@ int libxl_device_disk_del(libxl_ctx *ctx
     devid = libxl__device_disk_dev_number(disk->vdev, NULL, NULL);
     device.backend_domid    = disk->backend_domid;
     device.backend_devid    = devid;
-    device.backend_kind     =
-        (disk->backend == DISK_BACKEND_PHY) ? DEVICE_VBD : DEVICE_TAP;
+
+    switch (disk->backend) {
+        case DISK_BACKEND_PHY:
+            device.backend_kind = DEVICE_VBD;
+            break;
+        case DISK_BACKEND_TAP:
+            device.backend_kind = DEVICE_VBD;
+            break;
+        case DISK_BACKEND_QDISK:
+            device.backend_kind = DEVICE_QDISK;
+            break;
+        default:
+            LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "unrecognized disk backend type: %d\n",
+                       disk->backend);
+            rc = ERROR_INVAL;
+            goto out_free;
+    }
     device.domid            = domid;
     device.devid            = devid;
     device.kind             = DEVICE_VBD;
     rc = libxl__device_del(&gc, &device, wait);
     xs_rm(ctx->xsh, XBT_NULL, libxl__device_backend_path(&gc, &device));
     xs_rm(ctx->xsh, XBT_NULL, libxl__device_frontend_path(&gc, &device));
+out_free:
     libxl__free_all(&gc);
     return rc;
 }
diff -r 40b0954cb5d9 -r 6162ae4cc9a7 tools/libxl/libxl_device.c
--- a/tools/libxl/libxl_device.c	Thu Apr 07 10:06:51 2011 +0100
+++ b/tools/libxl/libxl_device.c	Thu Apr 07 10:06:51 2011 +0100
@@ -31,7 +31,6 @@
 static const char *string_of_kinds[] = {
     [DEVICE_VIF] = "vif",
     [DEVICE_VBD] = "vbd",
-    [DEVICE_TAP] = "tap",
     [DEVICE_QDISK] = "qdisk",
     [DEVICE_PCI] = "pci",
     [DEVICE_VFB] = "vfb",
@@ -135,7 +134,7 @@ char *libxl__device_disk_string_of_backe
 {
     switch (backend) {
         case DISK_BACKEND_QDISK: return "qdisk";
-        case DISK_BACKEND_TAP: return "tap";
+        case DISK_BACKEND_TAP: return "phy";
         case DISK_BACKEND_PHY: return "phy";
         default: return NULL;
     }
diff -r 40b0954cb5d9 -r 6162ae4cc9a7 tools/libxl/libxl_internal.h
--- a/tools/libxl/libxl_internal.h	Thu Apr 07 10:06:51 2011 +0100
+++ b/tools/libxl/libxl_internal.h	Thu Apr 07 10:06:51 2011 +0100
@@ -97,7 +97,6 @@ struct libxl__ctx {
 typedef enum {
     DEVICE_VIF = 1,
     DEVICE_VBD,
-    DEVICE_TAP,
     DEVICE_QDISK,
     DEVICE_PCI,
     DEVICE_VFB,

Re: [PATCH 7 of 7] libxl: Drop internal DEVICE_TAP backend type

[Ian Jackson]

Ian Campbell writes ("[Xen-devel] [PATCH 7 of 7] libxl: Drop internal DEVICE_TAP backend type"):
> libxl: Drop internal DEVICE_TAP backend type

Applied all seven, thanks.

Ian.

Re: [PATCH 0 of 7] libxl: refactor tap disk handling

[Christoph Egger]

On 04/07/11 11:52, Ian Campbell wrote:
> I'm not personally convinced that support for blktap2 devices should
> be conflated in libxl with the PV block backend support but given it's
> there lets at least correct it.
>
> In a blktap2 system there is no "tap" PV backend type. blktap2 exposes
> a standard block device and this is passed to a guest using the
> standard blkback "vbd" (sometimes called "phy") backend. Drop the
> "tap" backend type and associated (libxl internal ) DEVICE_TAP
> enumeration value.

What happens on a no-blktap2 system?

>
> Also try and clarify the paths which fallback from blktap2 to qdisk
> when the former is not present. Falling through a switch statement is
> a neat way of doing this in some cases, but I don't think this is one
> of them.
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>


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Re: [PATCH 0 of 7] libxl: refactor tap disk handling

[Ian Campbell]

On Thu, 2011-04-07 at 13:31 +0100, Christoph Egger wrote:
> On 04/07/11 11:52, Ian Campbell wrote:
> > I'm not personally convinced that support for blktap2 devices should
> > be conflated in libxl with the PV block backend support but given it's
> > there lets at least correct it.
> >
> > In a blktap2 system there is no "tap" PV backend type. blktap2 exposes
> > a standard block device and this is passed to a guest using the
> > standard blkback "vbd" (sometimes called "phy") backend. Drop the
> > "tap" backend type and associated (libxl internal ) DEVICE_TAP
> > enumeration value.
> 
> What happens on a no-blktap2 system?

Same as before, libxl__blktap_enabled still returns false and the same
things should happen as a result.

Ian.
> 
> >
> > Also try and clarify the paths which fallback from blktap2 to qdisk
> > when the former is not present. Falling through a switch statement is
> > a neat way of doing this in some cases, but I don't think this is one
> > of them.
> >
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> >
> 
>