Re: [Xen-devel]xl create PV guest with qcow/qcow2 disk images fail

[Chunyan Liu <cyliu@xxxxxxxx>]

Start qemu-nbd to mount non-raw qdisk in dom0 so that xl can create PV guest 
with qcow/qcow2 disk image and using pygrub.
v2: use fork and exec instead of system(3)

Signed-off-by: Chunyan Liu <cyliu@xxxxxxxx>

diff -r b4cf57bbc3fb tools/libxl/libxl.c
--- a/tools/libxl/libxl.c       Thu Oct 20 15:24:46 2011 +0800
+++ b/tools/libxl/libxl.c       Fri Oct 28 20:50:36 2011 +0800
@@ -1077,6 +1077,58 @@ out_free:
     libxl__free_all(&gc);
     return rc;
 }
+static int fork_exec(char *arg0, char **args)
+{
+    pid_t pid;
+    int status;
+
+    pid = fork();
+    if (pid < 0)
+        return -1;
+    else if (pid == 0){
+        execvp(arg0, args);
+        exit(127);
+    }
+    sleep(1);    
+    while (waitpid(pid, &status, 0) < 0) {
+        if (errno != EINTR) {
+            status = -1;
+            break;
+        }
+    }
+
+    return status;
+}
+
+static char * nbd_mount_disk(libxl__gc *gc, libxl_device_disk *disk)
+{
+    int i;
+    int nbds_max = 16;
+    char *nbd_dev = NULL;
+    char *args[] = {"qemu-nbd","-c",NULL,NULL,NULL};
+    char *ret = NULL;
+
+    for (i = 0; i < nbds_max; i++) {
+        nbd_dev = libxl__sprintf(gc, "/dev/nbd%d", i);
+        args[2] = libxl__sprintf(gc, "%s", nbd_dev);
+        args[3] = libxl__sprintf(gc, "%s", disk->pdev_path);
+        if (fork_exec(args[0], args) == 0) {
+            ret = strdup(nbd_dev);
+            break;
+        }
+    }
+
+    return ret;
+}
+
+static int nbd_unmount_disk(libxl__gc *gc, char *diskpath) {
+    char *args[] = {"qemu-nbd","-d",NULL,NULL};
+    args[2] = libxl__sprintf(gc, "%s", diskpath);
+    if (fork_exec(args[0], args))
+        return 0;
+    else
+        return ERROR_FAIL;
+}
 
 char * libxl_device_disk_local_attach(libxl_ctx *ctx, libxl_device_disk *disk)
 {
@@ -1084,6 +1136,7 @@ char * libxl_device_disk_local_attach(li
     char *dev = NULL;
     char *ret = NULL;
     int rc;
+    char *mdev = NULL;
 
     rc = libxl__device_disk_set_backend(&gc, disk);
     if (rc) goto out;
@@ -1118,8 +1171,12 @@ char * libxl_device_disk_local_attach(li
             break;
         case LIBXL_DISK_BACKEND_QDISK:
             if (disk->format != LIBXL_DISK_FORMAT_RAW) {
-                LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "cannot locally"
-                           " attach a qdisk image if the format is not raw");
+                LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "attaching a non-raw qdisk 
image to domain 0\n");
+                mdev = nbd_mount_disk(&gc, disk);
+                if (mdev)
+                    dev = mdev;
+                else
+                    LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "fail to mount image 
with qemu-nbd");
                 break;
             }
             LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "locally attaching qdisk %s\n",
@@ -1135,11 +1192,13 @@ char * libxl_device_disk_local_attach(li
  out:
     if (dev != NULL)
         ret = strdup(dev);
+    if (mdev)
+        free(mdev);
     libxl__free_all(&gc);
     return ret;
 }
 
-int libxl_device_disk_local_detach(libxl_ctx *ctx, libxl_device_disk *disk)
+int libxl_device_disk_local_detach(libxl_ctx *ctx, libxl_device_disk *disk, 
char *diskpath)
 {
     /* Nothing to do for PHYSTYPE_PHY. */
 
@@ -1147,7 +1206,22 @@ int libxl_device_disk_local_detach(libxl
      * For other device types assume that the blktap2 process is
      * needed by the soon to be started domain and do nothing.
      */
+    libxl__gc gc = LIBXL_INIT_GC(ctx);
+    int ret;
 
+    switch (disk->backend) {
+        case LIBXL_DISK_BACKEND_QDISK:
+            if (disk->format != LIBXL_DISK_FORMAT_RAW) {
+                LIBXL__LOG(ctx, LIBXL__LOG_DEBUG, "Locally detach a non-raw "
+                    "qdisk image");
+                ret = nbd_unmount_disk(&gc, diskpath);
+                return ret;
+            }
+        default:
+            break;
+    }
+
+    libxl__free_all(&gc);
     return 0;
 }
 
diff -r b4cf57bbc3fb tools/libxl/libxl.h
--- a/tools/libxl/libxl.h       Thu Oct 20 15:24:46 2011 +0800
+++ b/tools/libxl/libxl.h       Fri Oct 28 20:50:36 2011 +0800
@@ -390,7 +390,7 @@ int libxl_cdrom_insert(libxl_ctx *ctx, u
  * Make a disk available in this domain. Returns path to a device.
  */
 char * libxl_device_disk_local_attach(libxl_ctx *ctx, libxl_device_disk *disk);
-int libxl_device_disk_local_detach(libxl_ctx *ctx, libxl_device_disk *disk);
+int libxl_device_disk_local_detach(libxl_ctx *ctx, libxl_device_disk *disk, 
char *diskpath);
 
 int libxl_device_nic_init(libxl_device_nic *nic, int dev_num);
 int libxl_device_nic_add(libxl_ctx *ctx, uint32_t domid, libxl_device_nic 
*nic);
diff -r b4cf57bbc3fb tools/libxl/libxl_bootloader.c
--- a/tools/libxl/libxl_bootloader.c    Thu Oct 20 15:24:46 2011 +0800
+++ b/tools/libxl/libxl_bootloader.c    Fri Oct 28 20:50:36 2011 +0800
@@ -424,7 +424,7 @@ int libxl_run_bootloader(libxl_ctx *ctx,
     rc = 0;
 out_close:
     if (diskpath) {
-        libxl_device_disk_local_detach(ctx, disk);
+        libxl_device_disk_local_detach(ctx, disk, diskpath);
         free(diskpath);
     }
     if (fifo_fd > -1)

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