[PULL 09/12] qcow2: Add keep_data_file command-line option

[Kevin Wolf <kwolf@redhat.com>]

From: Hanna Czenczek <hreitz@redhat.com>

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>
---
 include/block/block_int-common.h |  1 +
 block/qcow2.c                    | 72 ++++++++++++++++++++++++++++++--
 tests/qemu-iotests/082.out       | 18 ++++++++
 3 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 9324af903d0..147c08155f7 100644
--- 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
 
diff --git a/block/qcow2.c b/block/qcow2.c
index e29810d86a3..e3728806203 100644
--- 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 */ }
diff --git a/tests/qemu-iotests/082.out b/tests/qemu-iotests/082.out
index d0dd333117a..e0463815c65 100644
--- 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
-- 
2.53.0