Markus Armbruster <arm...@redhat.com> writes:
> Peter Xu <pet...@redhat.com> writes:
>
>> On Fri, May 03, 2024 at 05:49:32PM -0300, Fabiano Rosas wrote:
>>> Peter Xu <pet...@redhat.com> writes:
>>>
>>> > On Fri, Apr 26, 2024 at 11:20:37AM -0300, Fabiano Rosas wrote:
>>> >> Add the direct-io migration parameter that tells the migration code to
>>> >> use O_DIRECT when opening the migration stream file whenever possible.
>>> >>
>>> >> This is currently only used with the mapped-ram migration that has a
>>> >> clear window guaranteed to perform aligned writes.
>>> >>
>>> >> Acked-by: Markus Armbruster <arm...@redhat.com>
>>> >> Signed-off-by: Fabiano Rosas <faro...@suse.de>
>>> >> ---
>>> >> include/qemu/osdep.h | 2 ++
>>> >> migration/migration-hmp-cmds.c | 11 +++++++++++
>>> >> migration/options.c | 30 ++++++++++++++++++++++++++++++
>>> >> migration/options.h | 1 +
>>> >> qapi/migration.json | 18 +++++++++++++++---
>>> >> util/osdep.c | 9 +++++++++
>>> >> 6 files changed, 68 insertions(+), 3 deletions(-)
>>> >>
>>> >> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
>>> >> index c7053cdc2b..645c14a65d 100644
>>> >> --- a/include/qemu/osdep.h
>>> >> +++ b/include/qemu/osdep.h
>>> >> @@ -612,6 +612,8 @@ int qemu_lock_fd_test(int fd, int64_t start, int64_t
>>> >> len, bool exclusive);
>>> >> bool qemu_has_ofd_lock(void);
>>> >> #endif
>>> >>
>>> >> +bool qemu_has_direct_io(void);
>>> >> +
>>> >> #if defined(__HAIKU__) && defined(__i386__)
>>> >> #define FMT_pid "%ld"
>>> >> #elif defined(WIN64)
>>> >> diff --git a/migration/migration-hmp-cmds.c
>>> >> b/migration/migration-hmp-cmds.c
>>> >> index 7e96ae6ffd..8496a2b34e 100644
>>> >> --- a/migration/migration-hmp-cmds.c
>>> >> +++ b/migration/migration-hmp-cmds.c
>>> >> @@ -397,6 +397,13 @@ void hmp_info_migrate_parameters(Monitor *mon,
>>> >> const QDict *qdict)
>>> >> monitor_printf(mon, "%s: %s\n",
>>> >> MigrationParameter_str(MIGRATION_PARAMETER_MODE),
>>> >> qapi_enum_lookup(&MigMode_lookup, params->mode));
>>> >> +
>>> >> + if (params->has_direct_io) {
>>> >> + monitor_printf(mon, "%s: %s\n",
>>> >> + MigrationParameter_str(
>>> >> + MIGRATION_PARAMETER_DIRECT_IO),
>>> >> + params->direct_io ? "on" : "off");
>>> >> + }
>>> >
>>> > This will be the first parameter to optionally display here. I think it's
>>> > a sign of misuse of has_direct_io field..
>
> Yes. For similar existing parameters, we do
>
> assert(params->has_FOO);
> monitor_printf(mon, "%s: '%s'\n",
> MigrationParameter_str(MIGRATION_PARAMETER_FOO),
> ... params->FOO as string ...)
>
>>> > IMHO has_direct_io should be best to be kept as "whether direct_io field
>>> > is
>>> > valid" and that's all of it. It hopefully shouldn't contain more
>>> > information than that, or otherwise it'll be another small challenge we
>>> > need to overcome when we can remove all these has_* fields, and can also
>>> > be
>>> > easily overlooked.
>>>
>>> I don't think I understand why we have those has_* fields. I thought my
>>> usage of 'params->has_direct_io = qemu_has_direct_io()' was the correct
>>> one, i.e. checking whether QEMU has any support for that parameter. Can
>>> you help me out here?
>>
>> Here params is the pointer to "struct MigrationParameters", which is
>> defined in qapi/migration.json. And we have had "has_*" only because we
>> allow optional fields with asterisks:
>>
>> { 'struct': 'MigrationParameters',
>> 'data': { '*announce-initial': 'size',
>> ...
>> } }
>>
>> So that's why it better only means "whether this field existed", because
>> it's how it is defined.
>>
>> IIRC we (or say, Markus) used to have some attempts deduplicates those
>> *MigrationParameter* things, and if success we have chance to drop has_*
>> fields (in which case we simply always have them; that "has_" makes more
>> sense only if in a QMP session to allow user only specify one or more
>> things if not all).
>
> qapi/migration.json:
>
> ##
> # @MigrationParameters:
> #
> --> # The optional members aren't actually optional.
> #
>
> In other words, the has_FOO generated for the members of
> MigrationParameters must all be true.
>
> These members became optional when we attempted to de-duplicate
> MigrationParameters and MigrateSetParameters, but failed (see commit
> de63ab61241 "migrate: Share common MigrationParameters struct" and
> commit 1bda8b3c695 "migration: Unshare MigrationParameters struct for
> now").
So what's the blocker for merging MigrationSetParameters and
MigrationParameters? Just the tls_* options?
