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Re: [Qemu-devel] [PATCH v3 3/5] block: qobject_is_equal() in bdrv_reopen
From: |
Max Reitz |
Subject: |
Re: [Qemu-devel] [PATCH v3 3/5] block: qobject_is_equal() in bdrv_reopen_prepare() |
Date: |
Wed, 5 Jul 2017 19:50:20 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 |
On 2017-07-05 09:14, Markus Armbruster wrote:
> Max Reitz <address@hidden> writes:
>
>> Currently, bdrv_reopen_prepare() assumes that all BDS options are
>> strings. However, this is not the case if the BDS has been created
>> through the json: pseudo-protocol or blockdev-add.
>>
>> Note that the user-invokable reopen command is an HMP command, so you
>> can only specify strings there. Therefore, specifying a non-string
>> option with the "same" value as it was when originally created will now
>> return an error because the values are supposedly similar (and there is
>> no way for the user to circumvent this but to just not specify the
>> option again -- however, this is still strictly better than just
>> crashing).
>>
>> Signed-off-by: Max Reitz <address@hidden>
>> ---
>> block.c | 31 ++++++++++++++++++-------------
>> 1 file changed, 18 insertions(+), 13 deletions(-)
>>
>> diff --git a/block.c b/block.c
>> index 913bb43..45eb248 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -2947,19 +2947,24 @@ int bdrv_reopen_prepare(BDRVReopenState
>> *reopen_state, BlockReopenQueue *queue,
>> const QDictEntry *entry = qdict_first(reopen_state->options);
>>
>> do {
>> - QString *new_obj = qobject_to_qstring(entry->value);
>> - const char *new = qstring_get_str(new_obj);
>> - /*
>> - * Caution: while qdict_get_try_str() is fine, getting
>> - * non-string types would require more care. When
>> - * bs->options come from -blockdev or blockdev_add, its
>> - * members are typed according to the QAPI schema, but
>> - * when they come from -drive, they're all QString.
>> - */
>> - const char *old = qdict_get_try_str(reopen_state->bs->options,
>> - entry->key);
>> -
>> - if (!old || strcmp(new, old)) {
>> + QObject *new = entry->value;
>> + QObject *old = qdict_get(reopen_state->bs->options, entry->key);
>> +
>> + /* TODO: When using -drive to specify blockdev options, all
>> values
>> + * will be strings; however, when using -blockdev, blockdev-add
>> or
>> + * filenames using the json:{} pseudo-protocol, they will be
>> + * correctly typed.
>> + * In contrast, reopening options are (currently) always strings
>> + * (because you can only specify them through qemu-io; all other
>> + * callers do not specify any options).
>> + * Therefore, when using anything other than -drive to create a
>> BDS,
>> + * this cannot detect non-string options as unchanged, because
>> + * qobject_is_equal() always returns false for objects of
>> different
>> + * type. In the future, this should be remedied by correctly
>> typing
>> + * all options. For now, this is not too big of an issue
>> because
>> + * the user simply can not specify options which cannot be
>> changed
>> + * anyway, so they will stay unchanged. */
>
> I'm not the maintainer, and this is not a demand: consider winging this
> comment and wrapping lines around column 70.
I actually did consider wrapping around column 70 and decided against it
because this comment is already indented by 12 characters, so none of
the lines exceed 65 characters (80 - (12 + strlen(" * "))).
About winging... For some reason I don't quite like it here. But it
probably is better because the comment is not immediately related to the
qobject_is_equal() call below, so I'll do it.
> As much as I fancy word play (see your reply to Eric), I have to admit
> that I had to read "the user simply can not specify options" about three
> times to make sense of it. Please consider a wording that's easier to
> grasp, perhaps "the user can simply refrain from specifying options that
> cannot be changed".
Aw. I've wanted this to be an example I could point people to to
educate them about the difference. Now, alas, none shall learn. :-(
Max
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[Qemu-devel] [PATCH v3 3/5] block: qobject_is_equal() in bdrv_reopen_prepare(), Max Reitz, 2017/07/03
Re: [Qemu-devel] [PATCH v3 3/5] block: qobject_is_equal() in bdrv_reopen_prepare(), Markus Armbruster, 2017/07/05
- Re: [Qemu-devel] [PATCH v3 3/5] block: qobject_is_equal() in bdrv_reopen_prepare(),
Max Reitz <=
[Qemu-devel] [PATCH v3 4/5] iotests: Add test for non-string option reopening, Max Reitz, 2017/07/03
[Qemu-devel] [PATCH v3 5/5] tests: Add check-qobject for equality tests, Max Reitz, 2017/07/03