[v2 4/4] block: Support detached LUKS header creation for blockdev-create

[Hyman Huang <yong.huang@smartx.com>]

Provide the "detached-mode" option for detached LUKS header
formatting.

To format the LUKS header on the pre-creating disk, example
as follows:

1. add a protocol blockdev node of LUKS header
$ virsh qemu-monitor-command vm '{"execute":"blockdev-add",
> "arguments":{"node-name":"libvirt-1-storage", "driver":"file",
> "filename":"/path/to/cipher.gluks" }}'

2. add the secret for encrypting the cipher stored in LUKS
   header above
$ virsh qemu-monitor-command vm '{"execute":"object-add",
> "arguments":{"qom-type": "secret", "id":
> "libvirt-1-storage-secret0", "data": "abc123"}}'

3. format the disk node
$ virsh qemu-monitor-command vm '{"execute":"blockdev-create",
> "arguments":{"job-id":"job0", "options":{"driver":"luks",
> "size":0, "file":"libvirt-1-storage", "detached-mode":true,
> "cipher-alg":"aes-256",
> "key-secret":"libvirt-3-storage-encryption-secret0"}}}'

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
---
 block/crypto.c       | 8 +++++++-
 qapi/block-core.json | 5 ++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/block/crypto.c b/block/crypto.c
index 7d70349463..e77c49bd0c 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -667,10 +667,12 @@ block_crypto_co_create_luks(BlockdevCreateOptions *create_options, Error **errp)
     BlockDriverState *bs = NULL;
     QCryptoBlockCreateOptions create_opts;
     PreallocMode preallocation = PREALLOC_MODE_OFF;
+    int64_t size;
     int ret;
 
     assert(create_options->driver == BLOCKDEV_DRIVER_LUKS);
     luks_opts = &create_options->u.luks;
+    size = luks_opts->size;
 
     bs = bdrv_co_open_blockdev_ref(luks_opts->file, errp);
     if (bs == NULL) {
@@ -686,7 +688,11 @@ block_crypto_co_create_luks(BlockdevCreateOptions *create_options, Error **errp)
         preallocation = luks_opts->preallocation;
     }
 
-    ret = block_crypto_co_create_generic(bs, luks_opts->size, &create_opts,
+    if (luks_opts->detached_mode) {
+        size = 0;
+    }
+
+    ret = block_crypto_co_create_generic(bs, size, &create_opts,
                                          preallocation, errp);
     if (ret < 0) {
         goto fail;
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 10be08d08f..1e7a7e1b05 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -4952,13 +4952,16 @@
 # @preallocation: Preallocation mode for the new image (since: 4.2)
 #     (default: off; allowed values: off, metadata, falloc, full)
 #
+# @detached-mode: create a detached LUKS header. (since 9.0)
+#
 # Since: 2.12
 ##
 { 'struct': 'BlockdevCreateOptionsLUKS',
   'base': 'QCryptoBlockCreateOptionsLUKS',
   'data': { 'file':             'BlockdevRef',
             'size':             'size',
-            '*preallocation':   'PreallocMode' } }
+            '*preallocation':   'PreallocMode',
+            '*detached-mode':   'bool'}}
 
 ##
 # @BlockdevCreateOptionsNfs:
-- 
2.39.1