block: Support detached LUKS header creation using qemu-img

Even though a LUKS header might be created with cryptsetup,
qemu-img should be enhanced to accommodate it as well.

Add the 'detached-header' option to specify the creation of
a detached LUKS header. This is how it is used:
$ qemu-img create --object secret,id=sec0,data=abc123 -f luks
> -o cipher-alg=aes-256,cipher-mode=xts -o key-secret=sec0
> -o detached-header=true header.luks

Using qemu-img or cryptsetup tools to query information of
an LUKS header image as follows:

Assume a detached LUKS header image has been created by:
$ dd if=/dev/zero of=test-header.img bs=1M count=32
$ dd if=/dev/zero of=test-payload.img bs=1M count=1000
$ cryptsetup luksFormat --header test-header.img test-payload.img
> --force-password --type luks1

Header image information could be queried using cryptsetup:
$ cryptsetup luksDump test-header.img

or qemu-img:
$ qemu-img info 'json:{"driver":"luks","file":{"filename":
> "test-payload.img"},"header":{"filename":"test-header.img"}}'

When using qemu-img, keep in mind that the entire disk
information specified by the JSON-format string above must be
supplied on the commandline; if not, an overlay check will reveal
a problem with the LUKS volume check logic.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
[changed to pass 'cflags' to block_crypto_co_create_generic]
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

block.c

@@ -7357,7 +7357,10 @@ void bdrv_img_create(const char *filename, const char *fmt,
         goto out;
     }
 
-    if (size == -1) {
+    /* Parameter 'size' is not needed for detached LUKS header */
+    if (size == -1 &&
+        !(!strcmp(fmt, "luks") &&
+          qemu_opt_get_bool(opts, "detached-header", false))) {
         error_setg(errp, "Image creation needs a size parameter");
         goto out;
     }

block/crypto.c

@@ -231,6 +231,7 @@ static QemuOptsList block_crypto_create_opts_luks = {
         BLOCK_CRYPTO_OPT_DEF_LUKS_IVGEN_HASH_ALG(""),
         BLOCK_CRYPTO_OPT_DEF_LUKS_HASH_ALG(""),
         BLOCK_CRYPTO_OPT_DEF_LUKS_ITER_TIME(""),
+        BLOCK_CRYPTO_OPT_DEF_LUKS_DETACHED_HEADER(""),
         { /* end of list */ }
     },
 };
@@ -405,7 +406,7 @@ block_crypto_co_create_generic(BlockDriverState *bs, int64_t size,
 
     data = (struct BlockCryptoCreateData) {
         .blk = blk,
-        .size = size,
+        .size = flags & QCRYPTO_BLOCK_CREATE_DETACHED ? 0 : size,
         .prealloc = prealloc,
     };
 
@@ -791,6 +792,9 @@ block_crypto_co_create_opts_luks(BlockDriver *drv, const char *filename,
     PreallocMode prealloc;
     char *buf = NULL;
     int64_t size;
+    bool detached_hdr =
+        qemu_opt_get_bool(opts, "detached-header", false);
+    unsigned int cflags = 0;
     int ret;
     Error *local_err = NULL;
 
@@ -830,9 +834,13 @@ block_crypto_co_create_opts_luks(BlockDriver *drv, const char *filename,
         goto fail;
     }
 
+    if (detached_hdr) {
+        cflags |= QCRYPTO_BLOCK_CREATE_DETACHED;
+    }
+
     /* Create format layer */
     ret = block_crypto_co_create_generic(bs, size, create_opts,
-                                         prealloc, 0, errp);
+                                         prealloc, cflags, errp);
     if (ret < 0) {
         goto fail;
     }

block/crypto.h

@@ -41,6 +41,7 @@
 #define BLOCK_CRYPTO_OPT_LUKS_IVGEN_HASH_ALG "ivgen-hash-alg"
 #define BLOCK_CRYPTO_OPT_LUKS_HASH_ALG "hash-alg"
 #define BLOCK_CRYPTO_OPT_LUKS_ITER_TIME "iter-time"
+#define BLOCK_CRYPTO_OPT_LUKS_DETACHED_HEADER "detached-header"
 #define BLOCK_CRYPTO_OPT_LUKS_KEYSLOT "keyslot"
 #define BLOCK_CRYPTO_OPT_LUKS_STATE "state"
 #define BLOCK_CRYPTO_OPT_LUKS_OLD_SECRET "old-secret"
@@ -100,6 +101,13 @@
         .help = "Select new state of affected keyslots (active/inactive)",\
     }
 
+#define BLOCK_CRYPTO_OPT_DEF_LUKS_DETACHED_HEADER(prefix)     \
+    {                                                         \
+        .name = prefix BLOCK_CRYPTO_OPT_LUKS_DETACHED_HEADER, \
+        .type = QEMU_OPT_BOOL,                                \
+        .help = "Create a detached LUKS header",              \
+    }
+
 #define BLOCK_CRYPTO_OPT_DEF_LUKS_KEYSLOT(prefix)              \
     {                                                          \
         .name = prefix BLOCK_CRYPTO_OPT_LUKS_KEYSLOT,          \

qapi/crypto.json

@@ -226,6 +226,8 @@
 # @iter-time: number of milliseconds to spend in PBKDF passphrase
 #     processing.  Currently defaults to 2000. (since 2.8)
 #
+# @detached-header: create a detached LUKS header. (since 9.0)
+#
 # Since: 2.6
 ##
 { 'struct': 'QCryptoBlockCreateOptionsLUKS',
@@ -235,7 +237,8 @@
             '*ivgen-alg': 'QCryptoIVGenAlgorithm',
             '*ivgen-hash-alg': 'QCryptoHashAlgorithm',
             '*hash-alg': 'QCryptoHashAlgorithm',
-            '*iter-time': 'int'}}
+            '*iter-time': 'int',
+            '*detached-header': 'bool'}}
 
 ##
 # @QCryptoBlockOpenOptions: