block_resize is safe to run in a coroutine, so use it as an example for
the new 'coroutine': true annotation in the QAPI schema.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
qapi/block-core.json | 3 ++-
blockdev.c | 6 +++---
2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 7ff5e5edaf..1dbb2a9901 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1341,7 +1341,8 @@
{ 'command': 'block_resize',
'data': { '*device': 'str',
'*node-name': 'str',
- 'size': 'int' } }
+ 'size': 'int' },
+ 'coroutine': true }
##
# @NewImageMode:
diff --git a/blockdev.c b/blockdev.c
index 8e029e9c01..b5e5d1e072 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
aio_context_release(aio_context);
}
-void qmp_block_resize(bool has_device, const char *device,
- bool has_node_name, const char *node_name,
- int64_t size, Error **errp)
+void coroutine_fn qmp_block_resize(bool has_device, const char *device,
+ bool has_node_name, const char *node_name,
+ int64_t size, Error **errp)
{
Error *local_err = NULL;
BlockBackend *blk = NULL;
--
2.20.1
Kevin Wolf <kwolf@redhat.com> writes:
> block_resize is safe to run in a coroutine, so use it as an example for
> the new 'coroutine': true annotation in the QAPI schema.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
> qapi/block-core.json | 3 ++-
> blockdev.c | 6 +++---
> 2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 7ff5e5edaf..1dbb2a9901 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1341,7 +1341,8 @@
> { 'command': 'block_resize',
> 'data': { '*device': 'str',
> '*node-name': 'str',
> - 'size': 'int' } }
> + 'size': 'int' },
> + 'coroutine': true }
>
> ##
> # @NewImageMode:
> diff --git a/blockdev.c b/blockdev.c
> index 8e029e9c01..b5e5d1e072 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
> aio_context_release(aio_context);
> }
>
> -void qmp_block_resize(bool has_device, const char *device,
> - bool has_node_name, const char *node_name,
> - int64_t size, Error **errp)
> +void coroutine_fn qmp_block_resize(bool has_device, const char *device,
> + bool has_node_name, const char *node_name,
> + int64_t size, Error **errp)
> {
> Error *local_err = NULL;
> BlockBackend *blk = NULL;
Pardon my ignorant question: what exactly makes a function a
coroutine_fn?
Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben:
> Kevin Wolf <kwolf@redhat.com> writes:
> > block_resize is safe to run in a coroutine, so use it as an example for
> > the new 'coroutine': true annotation in the QAPI schema.
> >
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > diff --git a/blockdev.c b/blockdev.c
> > index 8e029e9c01..b5e5d1e072 100644
> > --- a/blockdev.c
> > +++ b/blockdev.c
> > @@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
> > aio_context_release(aio_context);
> > }
> >
> > -void qmp_block_resize(bool has_device, const char *device,
> > - bool has_node_name, const char *node_name,
> > - int64_t size, Error **errp)
> > +void coroutine_fn qmp_block_resize(bool has_device, const char *device,
> > + bool has_node_name, const char *node_name,
> > + int64_t size, Error **errp)
> > {
> > Error *local_err = NULL;
> > BlockBackend *blk = NULL;
>
> Pardon my ignorant question: what exactly makes a function a
> coroutine_fn?
When Stefan requested adding the coroutine_fn marker, it seemed to make
sense to me because the QMP dispatcher will always call it from
coroutine context now, and being always run in coroutine context makes a
function a coroutine_fn.
However, it's also called from hmp_block_resize(), so at least for now
coroutine_fn is actually wrong.
Kevin
Kevin Wolf <kwolf@redhat.com> writes:
> Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben:
>> Kevin Wolf <kwolf@redhat.com> writes:
>> > block_resize is safe to run in a coroutine, so use it as an example for
>> > the new 'coroutine': true annotation in the QAPI schema.
>> >
>> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>
>> > diff --git a/blockdev.c b/blockdev.c
>> > index 8e029e9c01..b5e5d1e072 100644
>> > --- a/blockdev.c
>> > +++ b/blockdev.c
>> > @@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
>> > aio_context_release(aio_context);
>> > }
>> >
>> > -void qmp_block_resize(bool has_device, const char *device,
>> > - bool has_node_name, const char *node_name,
>> > - int64_t size, Error **errp)
>> > +void coroutine_fn qmp_block_resize(bool has_device, const char *device,
>> > + bool has_node_name, const char *node_name,
>> > + int64_t size, Error **errp)
>> > {
>> > Error *local_err = NULL;
>> > BlockBackend *blk = NULL;
>>
>> Pardon my ignorant question: what exactly makes a function a
>> coroutine_fn?
>
> When Stefan requested adding the coroutine_fn marker, it seemed to make
> sense to me because the QMP dispatcher will always call it from
> coroutine context now, and being always run in coroutine context makes a
> function a coroutine_fn.
>
> However, it's also called from hmp_block_resize(), so at least for now
> coroutine_fn is actually wrong.
This answers the question when we mark a function a coroutine_fn. I
meant to ask what conditions the function itself must satisfy to be
eligible for this mark.
Am 16.01.2020 um 16:13 hat Markus Armbruster geschrieben:
> Kevin Wolf <kwolf@redhat.com> writes:
>
> > Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben:
> >> Kevin Wolf <kwolf@redhat.com> writes:
> >> > block_resize is safe to run in a coroutine, so use it as an example for
> >> > the new 'coroutine': true annotation in the QAPI schema.
> >> >
> >> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> >> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> >
> >> > diff --git a/blockdev.c b/blockdev.c
> >> > index 8e029e9c01..b5e5d1e072 100644
> >> > --- a/blockdev.c
> >> > +++ b/blockdev.c
> >> > @@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
> >> > aio_context_release(aio_context);
> >> > }
> >> >
> >> > -void qmp_block_resize(bool has_device, const char *device,
> >> > - bool has_node_name, const char *node_name,
> >> > - int64_t size, Error **errp)
> >> > +void coroutine_fn qmp_block_resize(bool has_device, const char *device,
> >> > + bool has_node_name, const char *node_name,
> >> > + int64_t size, Error **errp)
> >> > {
> >> > Error *local_err = NULL;
> >> > BlockBackend *blk = NULL;
> >>
> >> Pardon my ignorant question: what exactly makes a function a
> >> coroutine_fn?
> >
> > When Stefan requested adding the coroutine_fn marker, it seemed to make
> > sense to me because the QMP dispatcher will always call it from
> > coroutine context now, and being always run in coroutine context makes a
> > function a coroutine_fn.
> >
> > However, it's also called from hmp_block_resize(), so at least for now
> > coroutine_fn is actually wrong.
>
> This answers the question when we mark a function a coroutine_fn. I
> meant to ask what conditions the function itself must satisfy to be
> eligible for this mark.
The requirement is actually not about the function itself, it's about
the callers, as stated above.
But being a coroutine_fn allows the function to call other functions
that only work in coroutine context (other coroutine_fns). In the end
the reason why a function only works in coroutine context is usually
that it (or any other coroutine_fns called by it) could yield, which
obviously doesn't work outside of coroutine contest.
Kevin
Kevin Wolf <kwolf@redhat.com> writes:
> Am 16.01.2020 um 16:13 hat Markus Armbruster geschrieben:
>> Kevin Wolf <kwolf@redhat.com> writes:
>>
>> > Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben:
>> >> Kevin Wolf <kwolf@redhat.com> writes:
>> >> > block_resize is safe to run in a coroutine, so use it as an example for
>> >> > the new 'coroutine': true annotation in the QAPI schema.
>> >> >
>> >> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>> >> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>> >
>> >> > diff --git a/blockdev.c b/blockdev.c
>> >> > index 8e029e9c01..b5e5d1e072 100644
>> >> > --- a/blockdev.c
>> >> > +++ b/blockdev.c
>> >> > @@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
>> >> > aio_context_release(aio_context);
>> >> > }
>> >> >
>> >> > -void qmp_block_resize(bool has_device, const char *device,
>> >> > - bool has_node_name, const char *node_name,
>> >> > - int64_t size, Error **errp)
>> >> > +void coroutine_fn qmp_block_resize(bool has_device, const char *device,
>> >> > + bool has_node_name, const char *node_name,
>> >> > + int64_t size, Error **errp)
>> >> > {
>> >> > Error *local_err = NULL;
>> >> > BlockBackend *blk = NULL;
>> >>
>> >> Pardon my ignorant question: what exactly makes a function a
>> >> coroutine_fn?
>> >
>> > When Stefan requested adding the coroutine_fn marker, it seemed to make
>> > sense to me because the QMP dispatcher will always call it from
>> > coroutine context now, and being always run in coroutine context makes a
>> > function a coroutine_fn.
>> >
>> > However, it's also called from hmp_block_resize(), so at least for now
>> > coroutine_fn is actually wrong.
>>
>> This answers the question when we mark a function a coroutine_fn. I
>> meant to ask what conditions the function itself must satisfy to be
>> eligible for this mark.
>
> The requirement is actually not about the function itself, it's about
> the callers, as stated above.
>
> But being a coroutine_fn allows the function to call other functions
> that only work in coroutine context (other coroutine_fns). In the end
> the reason why a function only works in coroutine context is usually
> that it (or any other coroutine_fns called by it) could yield, which
> obviously doesn't work outside of coroutine contest.
Thanks.
I think "being always run in coroutine context makes a function a
coroutine_fn" is inaccurate. It's "calling a coroutine_fn without
switching to coroutine context first when not already in coroutine
context". The induction terminates at basic coroutine_fn like
qemu_coroutine_yield().
Pertinent:
/**
* Return whether or not currently inside a coroutine
*
* This can be used to write functions that work both when in coroutine context
* and when not in coroutine context. Note that such functions cannot use the
* coroutine_fn annotation since they work outside coroutine context.
*/
bool qemu_in_coroutine(void);
For qmp_block_resize(), it's used like this, in bdrv_truncate():
if (qemu_in_coroutine()) {
/* Fast-path if already in coroutine context */
bdrv_truncate_co_entry(&tco);
} else {
co = qemu_coroutine_create(bdrv_truncate_co_entry, &tco);
bdrv_coroutine_enter(child->bs, co);
BDRV_POLL_WHILE(child->bs, tco.ret == NOT_DONE);
}
where bdrv_truncate_co_entry() is a coroutine_fn.
Am 17.01.2020 um 06:44 hat Markus Armbruster geschrieben:
> Kevin Wolf <kwolf@redhat.com> writes:
>
> > Am 16.01.2020 um 16:13 hat Markus Armbruster geschrieben:
> >> Kevin Wolf <kwolf@redhat.com> writes:
> >>
> >> > Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben:
> >> >> Kevin Wolf <kwolf@redhat.com> writes:
> >> >> > block_resize is safe to run in a coroutine, so use it as an example for
> >> >> > the new 'coroutine': true annotation in the QAPI schema.
> >> >> >
> >> >> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> >> >> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> >> >
> >> >> > diff --git a/blockdev.c b/blockdev.c
> >> >> > index 8e029e9c01..b5e5d1e072 100644
> >> >> > --- a/blockdev.c
> >> >> > +++ b/blockdev.c
> >> >> > @@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
> >> >> > aio_context_release(aio_context);
> >> >> > }
> >> >> >
> >> >> > -void qmp_block_resize(bool has_device, const char *device,
> >> >> > - bool has_node_name, const char *node_name,
> >> >> > - int64_t size, Error **errp)
> >> >> > +void coroutine_fn qmp_block_resize(bool has_device, const char *device,
> >> >> > + bool has_node_name, const char *node_name,
> >> >> > + int64_t size, Error **errp)
> >> >> > {
> >> >> > Error *local_err = NULL;
> >> >> > BlockBackend *blk = NULL;
> >> >>
> >> >> Pardon my ignorant question: what exactly makes a function a
> >> >> coroutine_fn?
> >> >
> >> > When Stefan requested adding the coroutine_fn marker, it seemed to make
> >> > sense to me because the QMP dispatcher will always call it from
> >> > coroutine context now, and being always run in coroutine context makes a
> >> > function a coroutine_fn.
> >> >
> >> > However, it's also called from hmp_block_resize(), so at least for now
> >> > coroutine_fn is actually wrong.
> >>
> >> This answers the question when we mark a function a coroutine_fn. I
> >> meant to ask what conditions the function itself must satisfy to be
> >> eligible for this mark.
> >
> > The requirement is actually not about the function itself, it's about
> > the callers, as stated above.
> >
> > But being a coroutine_fn allows the function to call other functions
> > that only work in coroutine context (other coroutine_fns). In the end
> > the reason why a function only works in coroutine context is usually
> > that it (or any other coroutine_fns called by it) could yield, which
> > obviously doesn't work outside of coroutine contest.
>
> Thanks.
>
> I think "being always run in coroutine context makes a function a
> coroutine_fn" is inaccurate. It's "calling a coroutine_fn without
> switching to coroutine context first when not already in coroutine
> context". The induction terminates at basic coroutine_fn like
> qemu_coroutine_yield().
I think we would tend to mark things as coroutine_fn even if they don't
call other coroutine_fns (yet), but would be allowed to. But this is now
really splitting hairs.
Maybe I should just have referred to the documentation in the source:
/**
* Mark a function that executes in coroutine context
*
* Functions that execute in coroutine context cannot be called directly from
* normal functions. In the future it would be nice to enable compiler or
* static checker support for catching such errors. This annotation might make
* it possible and in the meantime it serves as documentation.
*
* For example:
*
* static void coroutine_fn foo(void) {
* ....
* }
*/
#define coroutine_fn
Kevin
Kevin Wolf <kwolf@redhat.com> writes:
> Am 17.01.2020 um 06:44 hat Markus Armbruster geschrieben:
>> Kevin Wolf <kwolf@redhat.com> writes:
>>
>> > Am 16.01.2020 um 16:13 hat Markus Armbruster geschrieben:
>> >> Kevin Wolf <kwolf@redhat.com> writes:
>> >>
>> >> > Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben:
[...]
>> >> >> Pardon my ignorant question: what exactly makes a function a
>> >> >> coroutine_fn?
>> >> >
>> >> > When Stefan requested adding the coroutine_fn marker, it seemed to make
>> >> > sense to me because the QMP dispatcher will always call it from
>> >> > coroutine context now, and being always run in coroutine context makes a
>> >> > function a coroutine_fn.
>> >> >
>> >> > However, it's also called from hmp_block_resize(), so at least for now
>> >> > coroutine_fn is actually wrong.
>> >>
>> >> This answers the question when we mark a function a coroutine_fn. I
>> >> meant to ask what conditions the function itself must satisfy to be
>> >> eligible for this mark.
>> >
>> > The requirement is actually not about the function itself, it's about
>> > the callers, as stated above.
>> >
>> > But being a coroutine_fn allows the function to call other functions
>> > that only work in coroutine context (other coroutine_fns). In the end
>> > the reason why a function only works in coroutine context is usually
>> > that it (or any other coroutine_fns called by it) could yield, which
>> > obviously doesn't work outside of coroutine contest.
>>
>> Thanks.
>>
>> I think "being always run in coroutine context makes a function a
>> coroutine_fn" is inaccurate. It's "calling a coroutine_fn without
>> switching to coroutine context first when not already in coroutine
>> context". The induction terminates at basic coroutine_fn like
>> qemu_coroutine_yield().
>
> I think we would tend to mark things as coroutine_fn even if they don't
> call other coroutine_fns (yet), but would be allowed to. But this is now
> really splitting hairs.
Your hair-splitting is my education :)
> Maybe I should just have referred to the documentation in the source:
>
> /**
> * Mark a function that executes in coroutine context
> *
> * Functions that execute in coroutine context cannot be called directly from
> * normal functions. In the future it would be nice to enable compiler or
> * static checker support for catching such errors. This annotation might make
> * it possible and in the meantime it serves as documentation.
> *
> * For example:
> *
> * static void coroutine_fn foo(void) {
> * ....
> * }
> */
> #define coroutine_fn
I had read that, of course, but it didn't quite enlighten me, so I
asked.
Perhaps it would have if it said "Mark a function that expects to run in
coroutine context".
Kevin Wolf <kwolf@redhat.com> writes:
> Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben:
>> Kevin Wolf <kwolf@redhat.com> writes:
>> > block_resize is safe to run in a coroutine, so use it as an example for
>> > the new 'coroutine': true annotation in the QAPI schema.
>> >
>> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
>
>> > diff --git a/blockdev.c b/blockdev.c
>> > index 8e029e9c01..b5e5d1e072 100644
>> > --- a/blockdev.c
>> > +++ b/blockdev.c
>> > @@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
>> > aio_context_release(aio_context);
>> > }
>> >
>> > -void qmp_block_resize(bool has_device, const char *device,
>> > - bool has_node_name, const char *node_name,
>> > - int64_t size, Error **errp)
>> > +void coroutine_fn qmp_block_resize(bool has_device, const char *device,
>> > + bool has_node_name, const char *node_name,
>> > + int64_t size, Error **errp)
>> > {
>> > Error *local_err = NULL;
>> > BlockBackend *blk = NULL;
>>
>> Pardon my ignorant question: what exactly makes a function a
>> coroutine_fn?
>
> When Stefan requested adding the coroutine_fn marker, it seemed to make
> sense to me because the QMP dispatcher will always call it from
> coroutine context now, and being always run in coroutine context makes a
> function a coroutine_fn.
>
> However, it's also called from hmp_block_resize(), so at least for now
> coroutine_fn is actually wrong.
With the coroutine_fn dropped:
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Any plans to make more QMP commands 'coroutine': true?
Am 17.01.2020 um 09:13 hat Markus Armbruster geschrieben:
> Kevin Wolf <kwolf@redhat.com> writes:
>
> > Am 16.01.2020 um 10:45 hat Markus Armbruster geschrieben:
> >> Kevin Wolf <kwolf@redhat.com> writes:
> >> > block_resize is safe to run in a coroutine, so use it as an example for
> >> > the new 'coroutine': true annotation in the QAPI schema.
> >> >
> >> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> >> > Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> >
> >> > diff --git a/blockdev.c b/blockdev.c
> >> > index 8e029e9c01..b5e5d1e072 100644
> >> > --- a/blockdev.c
> >> > +++ b/blockdev.c
> >> > @@ -3161,9 +3161,9 @@ void hmp_drive_del(Monitor *mon, const QDict *qdict)
> >> > aio_context_release(aio_context);
> >> > }
> >> >
> >> > -void qmp_block_resize(bool has_device, const char *device,
> >> > - bool has_node_name, const char *node_name,
> >> > - int64_t size, Error **errp)
> >> > +void coroutine_fn qmp_block_resize(bool has_device, const char *device,
> >> > + bool has_node_name, const char *node_name,
> >> > + int64_t size, Error **errp)
> >> > {
> >> > Error *local_err = NULL;
> >> > BlockBackend *blk = NULL;
> >>
> >> Pardon my ignorant question: what exactly makes a function a
> >> coroutine_fn?
> >
> > When Stefan requested adding the coroutine_fn marker, it seemed to make
> > sense to me because the QMP dispatcher will always call it from
> > coroutine context now, and being always run in coroutine context makes a
> > function a coroutine_fn.
> >
> > However, it's also called from hmp_block_resize(), so at least for now
> > coroutine_fn is actually wrong.
>
> With the coroutine_fn dropped:
> Reviewed-by: Markus Armbruster <armbru@redhat.com>
>
> Any plans to make more QMP commands 'coroutine': true?
No immediate plans from me. Myself, I was interested in block_resize
because without the conversion, Max wanted me to jump through some hoops
with a bdrv_truncate() fix to make sure that it wouldn't block the guest
during block_resize.
Of course, apart from that, there is Marc-André's long-standing
screendump bug that will finally have all of the required
infrastructure (and I think I saw a patch on the list already).
Kevin
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