block: luks: better error message when creating too large files

Currently if you attampt to create too large file with luks you
get the following error message:

Formatting 'test.luks', fmt=luks size=17592186044416 key-secret=sec0
qemu-img: test.luks: Could not resize file: File too large

While for raw format the error message is
qemu-img: test.img: The image size is too large for file format 'raw'

The reason for this is that qemu-img checks for errono of the failure,
and presents the later error when it is -EFBIG

However crypto generic code 'swallows' the errno and replaces it
with -EIO.

As an attempt to make it better, we can make luks driver,
detect -EFBIG and in this case present a better error message,
which is what this patch does

The new error message is:

qemu-img: error creating test.luks: The requested file size is too large

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1534898


Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

block/crypto.c

@@ -104,18 +104,35 @@ static ssize_t block_crypto_init_func(QCryptoBlock *block,
                                       Error **errp)
 {
     struct BlockCryptoCreateData *data = opaque;
+    Error *local_error = NULL;
+    int ret;
 
     if (data->size > INT64_MAX || headerlen > INT64_MAX - data->size) {
-        error_setg(errp, "The requested file size is too large");
-        return -EFBIG;
+        ret = -EFBIG;
+        goto error;
     }
 
     /* User provided size should reflect amount of space made
      * available to the guest, so we must take account of that
      * which will be used by the crypto header
      */
-    return blk_truncate(data->blk, data->size + headerlen, false,
-                        data->prealloc, 0, errp);
+    ret = blk_truncate(data->blk, data->size + headerlen, false,
+                       data->prealloc, 0, &local_error);
+
+    if (ret >= 0) {
+        return ret;
+    }
+
+error:
+    if (ret == -EFBIG) {
+        /* Replace the error message with a better one */
+        error_free(local_error);
+        error_setg(errp, "The requested file size is too large");
+    } else {
+        error_propagate(errp, local_error);
+    }
+
+    return ret;
 }