Peter Xu <pet...@redhat.com> writes:
> On Mon, Nov 27, 2023 at 05:25:55PM -0300, Fabiano Rosas wrote:
>> Allow multifd to open file-backed channels. This will be used when
>> enabling the fixed-ram migration stream format which expects a
>> seekable transport.
>>
>> The QIOChannel read and write methods will use the preadv/pwritev
>> versions which don't update the file offset at each call so we can
>> reuse the fd without re-opening for every channel.
>>
>> Note that this is just setup code and multifd cannot yet make use of
>> the file channels.
>>
>> Signed-off-by: Fabiano Rosas <faro...@suse.de>
>> ---
>> - open multifd channels with O_WRONLY and no mode
>> - stop cancelling migration and propagate error via qio_task
>> ---
>> migration/file.c | 47 +++++++++++++++++++++++++++++++++++++++++--
>> migration/file.h | 5 +++++
>> migration/multifd.c | 14 +++++++++++--
>> migration/options.c | 7 +++++++
>> migration/options.h | 1 +
>> migration/qemu-file.h | 1 -
>> 6 files changed, 70 insertions(+), 5 deletions(-)
>>
>> diff --git a/migration/file.c b/migration/file.c
>> index 5d4975f43e..67d6f42da7 100644
>> --- a/migration/file.c
>> +++ b/migration/file.c
>> @@ -17,6 +17,10 @@
>>
>> #define OFFSET_OPTION ",offset="
>>
>> +static struct FileOutgoingArgs {
>> + char *fname;
>> +} outgoing_args;
>> +
>> /* Remove the offset option from @filespec and return it in @offsetp. */
>>
>> int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp)
>> @@ -36,6 +40,42 @@ int file_parse_offset(char *filespec, uint64_t *offsetp,
>> Error **errp)
>> return 0;
>> }
>>
>> +static void qio_channel_file_connect_worker(QIOTask *task, gpointer opaque)
>> +{
>> + /* noop */
>> +}
>> +
>> +int file_send_channel_destroy(QIOChannel *ioc)
>> +{
>> + if (ioc) {
>> + qio_channel_close(ioc, NULL);
>> + object_unref(OBJECT(ioc));
>> + }
>> + g_free(outgoing_args.fname);
>> + outgoing_args.fname = NULL;
>> +
>> + return 0;
>> +}
>> +
>> +void file_send_channel_create(QIOTaskFunc f, void *data)
>> +{
>> + QIOChannelFile *ioc;
>> + QIOTask *task;
>> + Error *err = NULL;
>> + int flags = O_WRONLY;
>> +
>> + ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, &err);
>> +
>> + task = qio_task_new(OBJECT(ioc), f, (gpointer)data, NULL);
>> + if (!ioc) {
>> + qio_task_set_error(task, err);
>> + return;
>> + }
>> +
>> + qio_task_run_in_thread(task, qio_channel_file_connect_worker,
>> + (gpointer)data, NULL, NULL);
>
> This is pretty weird. This invokes a thread, but it'll run a noop. It
> seems meaningless to me.
>
That's QIOTask weirdness isn't it? It will run the worker in the thread,
but it also schedules the completion function as a glib event. So that's
when multifd_new_send_channel_async() will run. The crucial aspect here
is that it gets dispatched by glib on the main loop. I'm just keeping
the model, except that I don't have work to do during the "connection"
phase.
> I assume you wanted to keep using the same async model as the socket typed
> multifd, but I don't think that works anyway, because file open blocks at
> qio_channel_file_new_path() so it's sync anyway.
It's async regarding multifd_channel_connect(). The connections will be
happening while multifd_save_setup() continues execution, IIUC.
>
> AFAICT we still share the code, as long as the file path properly invokes
> multifd_channel_connect() after the iochannel is setup.
>
I don't see the point in moving any of that logic into the URI
implementation. We already have the TLS handshake code which can also
call multifd_channel_connect() and that is a mess. IMO we should be
keeping the interface between multifd and the frontends as boilerplate
as possible.
>> +}
>> +
>> void file_start_outgoing_migration(MigrationState *s,
>> FileMigrationArgs *file_args, Error
>> **errp)
>> {
>> @@ -43,15 +83,18 @@ void file_start_outgoing_migration(MigrationState *s,
>> g_autofree char *filename = g_strdup(file_args->filename);
>> uint64_t offset = file_args->offset;
>> QIOChannel *ioc;
>> + int flags = O_CREAT | O_TRUNC | O_WRONLY;
>> + mode_t mode = 0660;
>>
>> trace_migration_file_outgoing(filename);
>>
>> - fioc = qio_channel_file_new_path(filename, O_CREAT | O_WRONLY | O_TRUNC,
>> - 0600, errp);
>> + fioc = qio_channel_file_new_path(filename, flags, mode, errp);
>> if (!fioc) {
>> return;
>> }
>>
>> + outgoing_args.fname = g_strdup(filename);
>> +
>> ioc = QIO_CHANNEL(fioc);
>> if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
>> return;
>> diff --git a/migration/file.h b/migration/file.h
>> index 37d6a08bfc..511019b319 100644
>> --- a/migration/file.h
>> +++ b/migration/file.h
>> @@ -9,10 +9,15 @@
>> #define QEMU_MIGRATION_FILE_H
>>
>> #include "qapi/qapi-types-migration.h"
>> +#include "io/task.h"
>> +#include "channel.h"
>>
>> void file_start_incoming_migration(FileMigrationArgs *file_args, Error
>> **errp);
>>
>> void file_start_outgoing_migration(MigrationState *s,
>> FileMigrationArgs *file_args, Error
>> **errp);
>> int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp);
>> +
>> +void file_send_channel_create(QIOTaskFunc f, void *data);
>> +int file_send_channel_destroy(QIOChannel *ioc);
>> #endif
>> diff --git a/migration/multifd.c b/migration/multifd.c
>> index 123ff0dec0..427740aab6 100644
>> --- a/migration/multifd.c
>> +++ b/migration/multifd.c
>> @@ -17,6 +17,7 @@
>> #include "exec/ramblock.h"
>> #include "qemu/error-report.h"
>> #include "qapi/error.h"
>> +#include "file.h"
>> #include "ram.h"
>> #include "migration.h"
>> #include "migration-stats.h"
>> @@ -28,6 +29,7 @@
>> #include "threadinfo.h"
>> #include "options.h"
>> #include "qemu/yank.h"
>> +#include "io/channel-file.h"
>> #include "io/channel-socket.h"
>> #include "yank_functions.h"
>>
>> @@ -511,7 +513,11 @@ static void multifd_send_terminate_threads(Error *err)
>>
>> static int multifd_send_channel_destroy(QIOChannel *send)
>> {
>> - return socket_send_channel_destroy(send);
>> + if (migrate_to_file()) {
>> + return file_send_channel_destroy(send);
>> + } else {
>> + return socket_send_channel_destroy(send);
>> + }
>> }
>>
>> void multifd_save_cleanup(void)
>> @@ -904,7 +910,11 @@ static void multifd_new_send_channel_async(QIOTask
>> *task, gpointer opaque)
>>
>> static void multifd_new_send_channel_create(gpointer opaque)
>> {
>> - socket_send_channel_create(multifd_new_send_channel_async, opaque);
>> + if (migrate_to_file()) {
>> + file_send_channel_create(multifd_new_send_channel_async, opaque);
>> + } else {
>> + socket_send_channel_create(multifd_new_send_channel_async, opaque);
>> + }
>> }
>>
>> int multifd_save_setup(Error **errp)
>> diff --git a/migration/options.c b/migration/options.c
>> index 10730b13ba..f671e24758 100644
>> --- a/migration/options.c
>> +++ b/migration/options.c
>> @@ -409,6 +409,13 @@ bool migrate_tls(void)
>> return s->parameters.tls_creds && *s->parameters.tls_creds;
>> }
>>
>> +bool migrate_to_file(void)
>> +{
>> + MigrationState *s = migrate_get_current();
>> +
>> + return qemu_file_is_seekable(s->to_dst_file);
>> +}
>
> Would this migrate_to_file() == migrate_multifd_packets()?
>
> Maybe we can keep using the other one and drop migrate_to_file?
>
Possibly the other way around as you mention. I'll take a look.
>> +
>> typedef enum WriteTrackingSupport {
>> WT_SUPPORT_UNKNOWN = 0,
>> WT_SUPPORT_ABSENT,
>> diff --git a/migration/options.h b/migration/options.h
>> index 8a19d6939c..84628a76e8 100644
>> --- a/migration/options.h
>> +++ b/migration/options.h
>> @@ -60,6 +60,7 @@ bool migrate_multifd_packets(void);
>> bool migrate_postcopy(void);
>> bool migrate_rdma(void);
>> bool migrate_tls(void);
>> +bool migrate_to_file(void);
>>
>> /* capabilities helpers */
>>
>> diff --git a/migration/qemu-file.h b/migration/qemu-file.h
>> index 32fd4a34fd..78ea21ab98 100644
>> --- a/migration/qemu-file.h
>> +++ b/migration/qemu-file.h
>> @@ -83,5 +83,4 @@ size_t qemu_get_buffer_at(QEMUFile *f, const uint8_t *buf,
>> size_t buflen,
>> off_t pos);
>>
>> QIOChannel *qemu_file_get_ioc(QEMUFile *file);
>> -
>> #endif
>> --
>> 2.35.3
>>
