[Qemu-devel] [PATCH 1/2] qcow2: include LUKS payload overhead in qemu-img measure

[Stefan Hajnoczi]

LUKS encryption reserves clusters for its own payload data.  The size of
this area must be included in the qemu-img measure calculation so that
we arrive at the correct minimum required image size.

(Ab)use the qcrypto_block_create() API to determine the payload
overhead.  We discard the payload data that qcrypto thinks will be
written to the image.

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 block/qcow2.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/block/qcow2.c b/block/qcow2.c
index 4897abae5e..7ab93a5d2f 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -4231,6 +4231,24 @@ static coroutine_fn int 
qcow2_co_flush_to_os(BlockDriverState *bs)
     return ret;
 }
 
+static ssize_t qcow2_measure_crypto_hdr_init_func(QCryptoBlock *block,
+        size_t headerlen, void *opaque, Error **errp)
+{
+    size_t *headerlenp = opaque;
+
+    /* Stash away the payload size */
+    *headerlenp = headerlen;
+    return 0;
+}
+
+static ssize_t qcow2_measure_crypto_hdr_write_func(QCryptoBlock *block,
+        size_t offset, const uint8_t *buf, size_t buflen,
+        void *opaque, Error **errp)
+{
+    /* Discard the bytes, we're not actually writing to an image */
+    return buflen;
+}
+
 static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, BlockDriverState *in_bs,
                                        Error **errp)
 {
@@ -4240,11 +4258,13 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, 
BlockDriverState *in_bs,
     uint64_t virtual_size; /* disk size as seen by guest */
     uint64_t refcount_bits;
     uint64_t l2_tables;
+    uint64_t luks_payload_size = 0;
     size_t cluster_size;
     int version;
     char *optstr;
     PreallocMode prealloc;
     bool has_backing_file;
+    bool has_luks;
 
     /* Parse image creation options */
     cluster_size = qcow2_opt_get_cluster_size_del(opts, &local_err);
@@ -4274,6 +4294,35 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, 
BlockDriverState *in_bs,
     has_backing_file = !!optstr;
     g_free(optstr);
 
+    optstr = qemu_opt_get_del(opts, BLOCK_OPT_ENCRYPT_FORMAT);
+    has_luks = optstr && strcmp(optstr, "luks") == 0;
+    g_free(optstr);
+
+    if (has_luks) {
+        QCryptoBlockCreateOptions cryptoopts = {
+            .format = Q_CRYPTO_BLOCK_FORMAT_LUKS,
+        };
+        QCryptoBlock *crypto;
+        size_t headerlen;
+
+        optstr = qemu_opt_get_del(opts, "encrypt.key-secret");
+        cryptoopts.u.luks.has_key_secret = !!optstr;
+        cryptoopts.u.luks.key_secret = optstr;
+
+        crypto = qcrypto_block_create(&cryptoopts, "encrypt.",
+                                      qcow2_measure_crypto_hdr_init_func,
+                                      qcow2_measure_crypto_hdr_write_func,
+                                      &headerlen, &local_err);
+
+        g_free(optstr);
+        if (!crypto) {
+            goto err;
+        }
+        qcrypto_block_free(crypto);
+
+        luks_payload_size = ROUND_UP(headerlen, cluster_size);
+    }
+
     virtual_size = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
     virtual_size = ROUND_UP(virtual_size, cluster_size);
 
@@ -4344,7 +4393,7 @@ static BlockMeasureInfo *qcow2_measure(QemuOpts *opts, 
BlockDriverState *in_bs,
     info = g_new(BlockMeasureInfo, 1);
     info->fully_allocated =
         qcow2_calc_prealloc_size(virtual_size, cluster_size,
-                                 ctz32(refcount_bits));
+                                 ctz32(refcount_bits)) + luks_payload_size;
 
     /* Remove data clusters that are not required.  This overestimates the
      * required size because metadata needed for the fully allocated file is
-- 
2.20.1