qcow2: Add keep_data_file command-line option

Add a command-line-only option to prevent overwriting the file specified as external data file. This option is only available on the qemu-img create command line, not via blockdev-create, as it makes no sense there: That interface separates file creation and formatting, so where the external data file attached to a newly formatted qcow2 node comes from is completely up to the user. Implementation detail: Enabling this option will not only not overwrite the external data file, but also assume it already exists, for two reasons: - It is simpler than checking whether the file exists, and only skipping creating it when it does not. It is therefore also less error-prone, i.e. we can never accidentally overwrite an existing file because we made some mistake in checking whether it exists. - I think it makes sense from a user's perspective: You set this option when you want to use an existing data file, and you unset it when you want a new one. Getting an error when you expect to use an existing data file seems to me a nice warning that something is not right. Signed-off-by: Hanna Czenczek <hreitz@redhat.com> Message-ID: <20250530084448.192369-2-hreitz@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> [kwolf: Removed redundant has_data_file_raw check] Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
1 year ago · 910451bc5b
3 changed files with 87 additions and 4 deletions
--- a/block/qcow2.c
+++ b/block/qcow2.c
@ -3991,6 +3991,8 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,
    BlockDriverState *bs = NULL;
    BlockDriverState *data_bs = NULL;
    const char *val;
+    bool keep_data_file = false;
+    BlockdevCreateOptionsQcow2 *qcow2_opts;
    int ret;

    /* Only the keyval visitor supports the dotted syntax needed for
@ -4022,6 +4024,22 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,
        qdict_put_str(qdict, BLOCK_OPT_COMPAT_LEVEL, "v3");
    }

+    val = qdict_get_try_str(qdict, BLOCK_OPT_KEEP_DATA_FILE);
+    if (val) {
+        if (!strcmp(val, "on")) {
+            keep_data_file = true;
+        } else if (!strcmp(val, "off")) {
+            keep_data_file = false;
+        } else {
+            error_setg(errp,
+                       "Invalid value '%s' for '%s': Must be 'on' or 'off'",
+                       val, BLOCK_OPT_KEEP_DATA_FILE);
+            ret = -EINVAL;
+            goto finish;
+        }
+        qdict_del(qdict, BLOCK_OPT_KEEP_DATA_FILE);
+    }
+
    /* Change legacy command line options into QMP ones */
    static const QDictRenames opt_renames[] = {
        { BLOCK_OPT_BACKING_FILE,       "backing-file" },
@ -4058,9 +4076,11 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,
    /* Create and open an external data file (protocol layer) */
    val = qdict_get_try_str(qdict, BLOCK_OPT_DATA_FILE);
    if (val) {
-        ret = bdrv_co_create_file(val, opts, false, errp);
-        if (ret < 0) {
-            goto finish;
+        if (!keep_data_file) {
+            ret = bdrv_co_create_file(val, opts, false, errp);
+            if (ret < 0) {
+                goto finish;
+            }
        }

        data_bs = bdrv_co_open(val, NULL, NULL,
@ -4073,6 +4093,11 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,

        qdict_del(qdict, BLOCK_OPT_DATA_FILE);
        qdict_put_str(qdict, "data-file", data_bs->node_name);
+    } else if (keep_data_file) {
+        error_setg(errp, "Must not use '%s=on' without '%s'",
+                   BLOCK_OPT_KEEP_DATA_FILE, BLOCK_OPT_DATA_FILE);
+        ret = -EINVAL;
+        goto finish;
    }

    /* Set 'driver' and 'node' options */
@ -4093,6 +4118,37 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,
        goto finish;
    }

+    qcow2_opts = &create_options->u.qcow2;
+
+    if (!qcow2_opts->has_preallocation) {
+        qcow2_opts->preallocation = PREALLOC_MODE_OFF;
+    }
+
+    if (keep_data_file &&
+        qcow2_opts->preallocation != PREALLOC_MODE_OFF &&
+        qcow2_opts->preallocation != PREALLOC_MODE_METADATA)
+    {
+        error_setg(errp, "Preallocating more than only metadata would "
+                   "overwrite the external data file's content and is "
+                   "therefore incompatible with '%s=on'",
+                   BLOCK_OPT_KEEP_DATA_FILE);
+        ret = -EINVAL;
+        goto finish;
+    }
+
+    if (keep_data_file &&
+        qcow2_opts->preallocation == PREALLOC_MODE_OFF &&
+        !qcow2_opts->data_file_raw)
+    {
+        error_setg(errp, "'%s=on' requires '%s=metadata' or '%s=on', or the "
+                   "file contents will not be visible",
+                   BLOCK_OPT_KEEP_DATA_FILE,
+                   BLOCK_OPT_PREALLOC,
+                   BLOCK_OPT_DATA_FILE_RAW);
+        ret = -EINVAL;
+        goto finish;
+    }
+
    /* Silently round up size */
    create_options->u.qcow2.size = ROUND_UP(create_options->u.qcow2.size,
                                            BDRV_SECTOR_SIZE);
@ -4103,7 +4159,9 @@ finish:
    if (ret < 0) {
        bdrv_graph_co_rdlock();
        bdrv_co_delete_file_noerr(bs);
-        bdrv_co_delete_file_noerr(data_bs);
+        if (!keep_data_file) {
+            bdrv_co_delete_file_noerr(data_bs);
+        }
        bdrv_graph_co_rdunlock();
    } else {
        ret = 0;
@ -6202,6 +6260,12 @@ static QemuOptsList qcow2_create_opts = {
            .help = "Compression method used for image cluster "        \
                    "compression",                                      \
            .def_value_str = "zlib"                                     \
+        },                                                              \
+        {                                                               \
+            .name = BLOCK_OPT_KEEP_DATA_FILE,                           \
+            .type = QEMU_OPT_BOOL,                                      \
+            .help = "Assume the external data file already exists and " \
+                    "do not overwrite it"                               \
        },
        QCOW_COMMON_OPTIONS,
        { /* end of list */ }
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@ -56,6 +56,7 @@
 #define BLOCK_OPT_DATA_FILE_RAW     "data_file_raw"
 #define BLOCK_OPT_COMPRESSION_TYPE  "compression_type"
 #define BLOCK_OPT_EXTL2             "extended_l2"
+#define BLOCK_OPT_KEEP_DATA_FILE    "keep_data_file"

 #define BLOCK_PROBE_BUF_SIZE        512

--- a/tests/qemu-iotests/082.out
+++ b/tests/qemu-iotests/082.out
@ -66,6 +66,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -92,6 +93,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -118,6 +120,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -144,6 +147,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -170,6 +174,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -196,6 +201,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -222,6 +228,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -248,6 +255,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -288,6 +296,7 @@ Supported qcow2 options:
  encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
  refcount_bits=<num>    - Width of a reference count entry in bits
@ -376,6 +385,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -402,6 +412,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -428,6 +439,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -454,6 +466,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -480,6 +493,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -506,6 +520,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -532,6 +547,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -558,6 +574,7 @@ Supported options:
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
  extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  nocow=<bool (on/off)>  - Turn off copy-on-write (valid only on btrfs)
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
@ -598,6 +615,7 @@ Supported qcow2 options:
  encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase
  encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
  extended_l2=<bool (on/off)> - Extended L2 tables
+  keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
  lazy_refcounts=<bool (on/off)> - Postpone refcount updates
  preallocation=<str>    - Preallocation mode (allowed values: off, metadata, falloc, full)
  refcount_bits=<num>    - Width of a reference count entry in bits