[PATCH v4 6/8] libxl: introduce libxl__alloc_vdev

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

Introduce libxl__alloc_vdev: find a spare virtual block device in the
domain passed as argument.

Changes in v4:
- rename libxl__devid_to_vdev to libxl__devid_to_localdev;
- introduce upper bound for encode_disk_name;
- better error handling;

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 tools/libxl/libxl_internal.c |   22 ++++++++++++++++++++
 tools/libxl/libxl_internal.h |    2 +
 tools/libxl/libxl_linux.c    |   45 ++++++++++++++++++++++++++++++++++++++++++
 tools/libxl/libxl_netbsd.c   |    6 +++++
 4 files changed, 75 insertions(+), 0 deletions(-)

diff --git a/tools/libxl/libxl_internal.c b/tools/libxl/libxl_internal.c
index f467572..ac73070 100644
--- a/tools/libxl/libxl_internal.c
+++ b/tools/libxl/libxl_internal.c
@@ -480,6 +480,28 @@ out:
     return rc;
 }
 
+static char * libxl__alloc_vdev(libxl__gc *gc, uint32_t domid,
+        char *blkdev_start, xs_transaction_t t)
+{
+    int devid = 0;
+    char *vdev = libxl__strdup(gc, blkdev_start);
+    char *dompath = libxl__xs_get_dompath(gc, domid);
+
+    do {
+        devid = libxl__device_disk_dev_number(vdev, NULL, NULL);
+        if (libxl__xs_read(gc, t,
+                    libxl__sprintf(gc, "%s/device/vbd/%d/backend",
+                        dompath, devid)) == NULL) {
+            if (errno == ENOENT)
+                return libxl__devid_to_localdev(gc, devid);
+            else
+                return NULL;
+        }
+        vdev[strlen(vdev) - 1]++;
+    } while (vdev[strlen(vdev) - 1] <= 'z');
+    return NULL;
+}
+
 _hidden char * libxl__device_disk_local_attach(libxl__gc *gc,
         const libxl_device_disk *disk,
         libxl_device_disk **new_disk,
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 97775fb..ed145ab 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -761,6 +761,8 @@ _hidden int libxl__ev_devstate_wait(libxl__gc *gc, libxl__ev_devstate *ds,
  */
 _hidden int libxl__try_phy_backend(mode_t st_mode);
 
+_hidden char *libxl__devid_to_localdev(libxl__gc *gc, int devid);
+
 /* from libxl_pci */
 
 _hidden int libxl__device_pci_add(libxl__gc *gc, uint32_t domid, libxl_device_pci *pcidev, int starting);
diff --git a/tools/libxl/libxl_linux.c b/tools/libxl/libxl_linux.c
index 925248b..cb596a9 100644
--- a/tools/libxl/libxl_linux.c
+++ b/tools/libxl/libxl_linux.c
@@ -25,3 +25,48 @@ int libxl__try_phy_backend(mode_t st_mode)
 
     return 1;
 }
+
+#define EXT_SHIFT 28
+#define EXTENDED (1<<EXT_SHIFT)
+#define VDEV_IS_EXTENDED(dev) ((dev)&(EXTENDED))
+#define BLKIF_MINOR_EXT(dev) ((dev)&(~EXTENDED))
+
+/* same as in Linux */
+static char *encode_disk_name(char *ptr, unsigned int n)
+{
+    if (n >= 26)
+        ptr = encode_disk_name(ptr, n / 26 - 1);
+    *ptr = 'a' + n % 26;
+    return ptr + 1;
+}
+
+char *libxl__devid_to_localdev(libxl__gc *gc, int devid)
+{
+    int minor;
+    int offset;
+    int nr_parts;
+    char *ptr = NULL;
+    char *ret = libxl__zalloc(gc, 32);
+
+    if (!VDEV_IS_EXTENDED(devid)) {
+        minor = devid & 0xff;
+        nr_parts = 16;
+    } else {
+        minor = BLKIF_MINOR_EXT(devid);
+        nr_parts = 256;
+    }
+    offset = minor / nr_parts;
+
+	/* arbitrary upper bound */
+	if (offset > 676)
+		return NULL;
+
+    strcpy(ret, "xvd");
+    ptr = encode_disk_name(ret + 3, offset);
+    if (minor % nr_parts == 0)
+        *ptr = 0;
+    else
+        snprintf(ptr, ret + 32 - ptr,
+                "%d", minor & (nr_parts - 1));
+    return ret;
+}
diff --git a/tools/libxl/libxl_netbsd.c b/tools/libxl/libxl_netbsd.c
index 9e0ed6d..dbf5f71 100644
--- a/tools/libxl/libxl_netbsd.c
+++ b/tools/libxl/libxl_netbsd.c
@@ -24,3 +24,9 @@ int libxl__try_phy_backend(mode_t st_mode)
 
     return 0;
 }
+
+char *libxl__devid_to_localdev(libxl__gc *gc, int devid)
+{
+    /* TODO */
+    return NULL;
+}
-- 
1.7.2.5