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>
Hanna Czenczek committed
May 30, 2025 at 10:44 UTC
910451bc5b08b45863e173b58cbf2288b82d9fd2
3 files changed
+87
-4
block/qcow2.c
+68
-4
@@ -3991,6 +3991,8 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,
3991
BlockDriverState *bs = NULL;
3992
BlockDriverState *data_bs = NULL;
3993
const char *val;
3994
+ bool keep_data_file = false;
3995
+ BlockdevCreateOptionsQcow2 *qcow2_opts;
3996
int ret;
3997
3998
/* 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,
4024
qdict_put_str(qdict, BLOCK_OPT_COMPAT_LEVEL, "v3");
4025
}
4026
4027
+ val = qdict_get_try_str(qdict, BLOCK_OPT_KEEP_DATA_FILE);
4028
+ if (val) {
4029
+ if (!strcmp(val, "on")) {
4030
+ keep_data_file = true;
4031
+ } else if (!strcmp(val, "off")) {
4032
+ keep_data_file = false;
4033
+ } else {
4034
+ error_setg(errp,
4035
+ "Invalid value '%s' for '%s': Must be 'on' or 'off'",
4036
+ val, BLOCK_OPT_KEEP_DATA_FILE);
4037
+ ret = -EINVAL;
4038
+ goto finish;
4039
+ }
4040
+ qdict_del(qdict, BLOCK_OPT_KEEP_DATA_FILE);
4041
+ }
4042
+
4043
/* Change legacy command line options into QMP ones */
4044
static const QDictRenames opt_renames[] = {
4045
{ BLOCK_OPT_BACKING_FILE, "backing-file" },
@@ -4058,9 +4076,11 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,
4076
/* Create and open an external data file (protocol layer) */
4077
val = qdict_get_try_str(qdict, BLOCK_OPT_DATA_FILE);
4078
if (val) {
4061
- ret = bdrv_co_create_file(val, opts, false, errp);
4062
- if (ret < 0) {
4063
- goto finish;
4079
+ if (!keep_data_file) {
4080
+ ret = bdrv_co_create_file(val, opts, false, errp);
4081
+ if (ret < 0) {
4082
+ goto finish;
4083
+ }
4084
}
4085
4086
data_bs = bdrv_co_open(val, NULL, NULL,
@@ -4073,6 +4093,11 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,
4093
4094
qdict_del(qdict, BLOCK_OPT_DATA_FILE);
4095
qdict_put_str(qdict, "data-file", data_bs->node_name);
4096
+ } else if (keep_data_file) {
4097
+ error_setg(errp, "Must not use '%s=on' without '%s'",
4098
+ BLOCK_OPT_KEEP_DATA_FILE, BLOCK_OPT_DATA_FILE);
4099
+ ret = -EINVAL;
4100
+ goto finish;
4101
}
4102
4103
/* Set 'driver' and 'node' options */
@@ -4093,6 +4118,37 @@ qcow2_co_create_opts(BlockDriver *drv, const char *filename, QemuOpts *opts,
4118
goto finish;
4119
}
4120
4121
+ qcow2_opts = &create_options->u.qcow2;
4122
+
4123
+ if (!qcow2_opts->has_preallocation) {
4124
+ qcow2_opts->preallocation = PREALLOC_MODE_OFF;
4125
+ }
4126
+
4127
+ if (keep_data_file &&
4128
+ qcow2_opts->preallocation != PREALLOC_MODE_OFF &&
4129
+ qcow2_opts->preallocation != PREALLOC_MODE_METADATA)
4130
+ {
4131
+ error_setg(errp, "Preallocating more than only metadata would "
4132
+ "overwrite the external data file's content and is "
4133
+ "therefore incompatible with '%s=on'",
4134
+ BLOCK_OPT_KEEP_DATA_FILE);
4135
+ ret = -EINVAL;
4136
+ goto finish;
4137
+ }
4138
+
4139
+ if (keep_data_file &&
4140
+ qcow2_opts->preallocation == PREALLOC_MODE_OFF &&
4141
+ !qcow2_opts->data_file_raw)
4142
+ {
4143
+ error_setg(errp, "'%s=on' requires '%s=metadata' or '%s=on', or the "
4144
+ "file contents will not be visible",
4145
+ BLOCK_OPT_KEEP_DATA_FILE,
4146
+ BLOCK_OPT_PREALLOC,
4147
+ BLOCK_OPT_DATA_FILE_RAW);
4148
+ ret = -EINVAL;
4149
+ goto finish;
4150
+ }
4151
+
4152
/* Silently round up size */
4153
create_options->u.qcow2.size = ROUND_UP(create_options->u.qcow2.size,
4154
BDRV_SECTOR_SIZE);
@@ -4103,7 +4159,9 @@ finish:
4159
if (ret < 0) {
4160
bdrv_graph_co_rdlock();
4161
bdrv_co_delete_file_noerr(bs);
4106
- bdrv_co_delete_file_noerr(data_bs);
4162
+ if (!keep_data_file) {
4163
+ bdrv_co_delete_file_noerr(data_bs);
4164
+ }
4165
bdrv_graph_co_rdunlock();
4166
} else {
4167
ret = 0;
@@ -6202,6 +6260,12 @@ static QemuOptsList qcow2_create_opts = {
6260
.help = "Compression method used for image cluster " \
6261
"compression", \
6262
.def_value_str = "zlib" \
6263
+ }, \
6264
+ { \
6265
+ .name = BLOCK_OPT_KEEP_DATA_FILE, \
6266
+ .type = QEMU_OPT_BOOL, \
6267
+ .help = "Assume the external data file already exists and " \
6268
+ "do not overwrite it" \
6269
},
6270
QCOW_COMMON_OPTIONS,
6271
{ /* end of list */ }
include/block/block_int-common.h
+1
@@ -56,6 +56,7 @@
56
#define BLOCK_OPT_DATA_FILE_RAW "data_file_raw"
57
#define BLOCK_OPT_COMPRESSION_TYPE "compression_type"
58
#define BLOCK_OPT_EXTL2 "extended_l2"
59
+#define BLOCK_OPT_KEEP_DATA_FILE "keep_data_file"
60
61
#define BLOCK_PROBE_BUF_SIZE 512
62
tests/qemu-iotests/082.out
+18
@@ -66,6 +66,7 @@ Supported options:
66
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
67
extended_l2=<bool (on/off)> - Extended L2 tables
68
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
69
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
70
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
71
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
72
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -92,6 +93,7 @@ Supported options:
93
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
94
extended_l2=<bool (on/off)> - Extended L2 tables
95
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
96
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
97
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
98
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
99
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -118,6 +120,7 @@ Supported options:
120
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
121
extended_l2=<bool (on/off)> - Extended L2 tables
122
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
123
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
124
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
125
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
126
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -144,6 +147,7 @@ Supported options:
147
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
148
extended_l2=<bool (on/off)> - Extended L2 tables
149
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
150
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
151
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
152
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
153
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -170,6 +174,7 @@ Supported options:
174
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
175
extended_l2=<bool (on/off)> - Extended L2 tables
176
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
177
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
178
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
179
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
180
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -196,6 +201,7 @@ Supported options:
201
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
202
extended_l2=<bool (on/off)> - Extended L2 tables
203
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
204
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
205
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
206
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
207
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -222,6 +228,7 @@ Supported options:
228
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
229
extended_l2=<bool (on/off)> - Extended L2 tables
230
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
231
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
232
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
233
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
234
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -248,6 +255,7 @@ Supported options:
255
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
256
extended_l2=<bool (on/off)> - Extended L2 tables
257
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
258
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
259
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
260
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
261
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -288,6 +296,7 @@ Supported qcow2 options:
296
encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase
297
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
298
extended_l2=<bool (on/off)> - Extended L2 tables
299
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
300
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
301
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
302
refcount_bits=<num> - Width of a reference count entry in bits
@@ -376,6 +385,7 @@ Supported options:
385
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
386
extended_l2=<bool (on/off)> - Extended L2 tables
387
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
388
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
389
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
390
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
391
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -402,6 +412,7 @@ Supported options:
412
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
413
extended_l2=<bool (on/off)> - Extended L2 tables
414
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
415
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
416
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
417
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
418
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -428,6 +439,7 @@ Supported options:
439
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
440
extended_l2=<bool (on/off)> - Extended L2 tables
441
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
442
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
443
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
444
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
445
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -454,6 +466,7 @@ Supported options:
466
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
467
extended_l2=<bool (on/off)> - Extended L2 tables
468
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
469
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
470
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
471
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
472
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -480,6 +493,7 @@ Supported options:
493
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
494
extended_l2=<bool (on/off)> - Extended L2 tables
495
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
496
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
497
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
498
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
499
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -506,6 +520,7 @@ Supported options:
520
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
521
extended_l2=<bool (on/off)> - Extended L2 tables
522
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
523
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
524
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
525
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
526
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -532,6 +547,7 @@ Supported options:
547
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
548
extended_l2=<bool (on/off)> - Extended L2 tables
549
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
550
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
551
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
552
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
553
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -558,6 +574,7 @@ Supported options:
574
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
575
extended_l2=<bool (on/off)> - Extended L2 tables
576
extent_size_hint=<size> - Extent size hint for the image file, 0 to disable
577
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
578
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
579
nocow=<bool (on/off)> - Turn off copy-on-write (valid only on btrfs)
580
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
@@ -598,6 +615,7 @@ Supported qcow2 options:
615
encrypt.key-secret=<str> - ID of secret providing qcow AES key or LUKS passphrase
616
encryption=<bool (on/off)> - Encrypt the image with format 'aes'. (Deprecated in favor of encrypt.format=aes)
617
extended_l2=<bool (on/off)> - Extended L2 tables
618
+ keep_data_file=<bool (on/off)> - Assume the external data file already exists and do not overwrite it
619
lazy_refcounts=<bool (on/off)> - Postpone refcount updates
620
preallocation=<str> - Preallocation mode (allowed values: off, metadata, falloc, full)
621
refcount_bits=<num> - Width of a reference count entry in bits