qcow2: Store data file name in the image

Rather than requiring that the external data file node is passed
explicitly when creating the qcow2 node, store the filename in the
designated header extension during .bdrv_create and read it from there
as a default during .bdrv_open.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

2 files changed, 94 insertions, 1 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index c20141b4e7..f32ddda2a7 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -398,6 +398,21 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
 #endif
             break;
 
+        case QCOW2_EXT_MAGIC_DATA_FILE:
+        {
+            s->image_data_file = g_malloc0(ext.len + 1);
+            ret = bdrv_pread(bs->file, offset, s->image_data_file, ext.len);
+            if (ret < 0) {
+                error_setg_errno(errp, -ret,
+                                 "ERROR: Could not read data file name");
+                return ret;
+            }
+#ifdef DEBUG_EXT
+            printf("Qcow2: Got external data file %s\n", s->image_data_file);
+#endif
+            break;
+        }
+
         default:
             /* unknown magic - save it in case we need to rewrite the header */
             /* If you add a new feature, make sure to also update the fast
@@ -1463,6 +1478,15 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
     }
 
     if (s->incompatible_features & QCOW2_INCOMPAT_DATA_FILE) {
+        if (!s->data_file && s->image_data_file) {
+            s->data_file = bdrv_open_child(s->image_data_file, options,
+                                           "data-file", bs, &child_file,
+                                           false, errp);
+            if (!s->data_file) {
+                ret = -EINVAL;
+                goto fail;
+            }
+        }
         if (!s->data_file) {
             error_setg(errp, "'data-file' is required for this image");
             ret = -EINVAL;
@@ -1650,6 +1674,7 @@ static int coroutine_fn qcow2_do_open(BlockDriverState *bs, QDict *options,
     return ret;
 
  fail:
+    g_free(s->image_data_file);
     if (has_data_file(bs)) {
         bdrv_unref_child(bs, s->data_file);
     }
@@ -2269,6 +2294,7 @@ static void qcow2_close(BlockDriverState *bs)
     g_free(s->unknown_header_fields);
     cleanup_unknown_header_ext(bs);
 
+    g_free(s->image_data_file);
     g_free(s->image_backing_file);
     g_free(s->image_backing_format);
 
@@ -2445,6 +2471,19 @@ int qcow2_update_header(BlockDriverState *bs)
         buflen -= ret;
     }
 
+    /* External data file header extension */
+    if (has_data_file(bs) && s->image_data_file) {
+        ret = header_ext_add(buf, QCOW2_EXT_MAGIC_DATA_FILE,
+                             s->image_data_file, strlen(s->image_data_file),
+                             buflen);
+        if (ret < 0) {
+            goto fail;
+        }
+
+        buf += ret;
+        buflen -= ret;
+    }
+
     /* Full disk encryption header pointer extension */
     if (s->crypto_header.offset != 0) {
         s->crypto_header.offset = cpu_to_be64(s->crypto_header.offset);
@@ -3086,6 +3125,12 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
         abort();
     }
 
+    /* Set the external data file if necessary */
+    if (data_bs) {
+        BDRVQcow2State *s = blk_bs(blk)->opaque;
+        s->image_data_file = g_strdup(data_bs->filename);
+    }
+
     /* Create a full header (including things like feature table) */
     ret = qcow2_update_header(blk_bs(blk));
     if (ret < 0) {
@@ -3165,6 +3210,7 @@ static int coroutine_fn qcow2_co_create_opts(const char *filename, QemuOpts *opt
     QDict *qdict;
     Visitor *v;
     BlockDriverState *bs = NULL;
+    BlockDriverState *data_bs = NULL;
     Error *local_err = NULL;
     const char *val;
     int ret;
@@ -3228,6 +3274,26 @@ static int coroutine_fn qcow2_co_create_opts(const char *filename, QemuOpts *opt
         goto finish;
     }
 
+    /* Create and open an external data file (protocol layer) */
+    val = qdict_get_try_str(qdict, BLOCK_OPT_DATA_FILE);
+    if (val) {
+        ret = bdrv_create_file(val, opts, errp);
+        if (ret < 0) {
+            goto finish;
+        }
+
+        data_bs = bdrv_open(val, NULL, NULL,
+                            BDRV_O_RDWR | BDRV_O_RESIZE | BDRV_O_PROTOCOL,
+                            errp);
+        if (data_bs == NULL) {
+            ret = -EIO;
+            goto finish;
+        }
+
+        qdict_del(qdict, BLOCK_OPT_DATA_FILE);
+        qdict_put_str(qdict, "data-file", data_bs->node_name);
+    }
+
     /* Set 'driver' and 'node' options */
     qdict_put_str(qdict, "driver", "qcow2");
     qdict_put_str(qdict, "file", bs->node_name);
@@ -3262,6 +3328,7 @@ static int coroutine_fn qcow2_co_create_opts(const char *filename, QemuOpts *opt
 finish:
     qobject_unref(qdict);
     bdrv_unref(bs);
+    bdrv_unref(data_bs);
     qapi_free_BlockdevCreateOptions(create_options);
     return ret;
 }
@@ -4552,6 +4619,8 @@ static ImageInfoSpecific *qcow2_get_specific_info(BlockDriverState *bs,
             .refcount_bits      = s->refcount_bits,
             .has_bitmaps        = !!bitmaps,
             .bitmaps            = bitmaps,
+            .has_data_file      = !!s->image_data_file,
+            .data_file          = g_strdup(s->image_data_file),
         };
     } else {
         /* if this assertion fails, this probably means a new version was
@@ -4754,7 +4823,7 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
     BDRVQcow2State *s = bs->opaque;
     int old_version = s->qcow_version, new_version = old_version;
     uint64_t new_size = 0;
-    const char *backing_file = NULL, *backing_format = NULL;
+    const char *backing_file = NULL, *backing_format = NULL, *data_file = NULL;
     bool lazy_refcounts = s->use_lazy_refcounts;
     const char *compat = NULL;
     uint64_t cluster_size = s->cluster_size;
@@ -4836,6 +4905,13 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
                            "may not exceed 64 bits");
                 return -EINVAL;
             }
+        } else if (!strcmp(desc->name, BLOCK_OPT_DATA_FILE)) {
+            data_file = qemu_opt_get(opts, BLOCK_OPT_DATA_FILE);
+            if (data_file && !has_data_file(bs)) {
+                error_setg(errp, "data-file can only be set for images that "
+                                 "use an external data file");
+                return -EINVAL;
+            }
         } else {
             /* if this point is reached, this probably means a new option was
              * added without having it covered here */
@@ -4882,6 +4958,17 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
         }
     }
 
+    if (data_file) {
+        g_free(s->image_data_file);
+        s->image_data_file = *data_file ? g_strdup(data_file) : NULL;
+    }
+
+    ret = qcow2_update_header(bs);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "Failed to update the image header");
+        return ret;
+    }
+
     if (backing_file || backing_format) {
         ret = qcow2_change_backing_file(bs,
                     backing_file ?: s->image_backing_file,
@@ -5030,6 +5117,11 @@ static QemuOptsList qcow2_create_opts = {
             .help = "Image format of the base image"
         },
         {
+            .name = BLOCK_OPT_DATA_FILE,
+            .type = QEMU_OPT_STRING,
+            .help = "File name of an external data file"
+        },
+        {
             .name = BLOCK_OPT_ENCRYPT,
             .type = QEMU_OPT_BOOL,
             .help = "Encrypt the image with format 'aes'. (Deprecated "
diff --git a/block/qcow2.h b/block/qcow2.h
index f23c003a46..a9c9cb4a26 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -343,6 +343,7 @@ typedef struct BDRVQcow2State {
      * override) */
     char *image_backing_file;
     char *image_backing_format;
+    char *image_data_file;
 
     CoQueue compress_wait_queue;
     int nb_compress_threads;