Re: [PATCH v2 20/29] migration/multifd: Add incoming QIOChannelFile support

[Peter Xu <peterx@redhat.com>]

On Mon, Oct 23, 2023 at 05:35:59PM -0300, Fabiano Rosas wrote:
> On the receiving side we don't need to differentiate between main
> channel and threads, so whichever channel is defined first gets to be
> the main one. And since there are no packets, use the atomic channel
> count to index into the params array.
> 
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  migration/file.c      | 39 +++++++++++++++++++++++++++++----------
>  migration/migration.c |  2 ++
>  migration/multifd.c   |  7 ++++++-
>  migration/multifd.h   |  1 +
>  4 files changed, 38 insertions(+), 11 deletions(-)
> 
> diff --git a/migration/file.c b/migration/file.c
> index 93b9b7bf5d..ad75225f43 100644
> --- a/migration/file.c
> +++ b/migration/file.c
> @@ -6,13 +6,15 @@
>   */
>  
>  #include "qemu/osdep.h"
> -#include "qemu/cutils.h"
>  #include "qapi/error.h"
> +#include "qemu/cutils.h"
> +#include "qemu/error-report.h"
>  #include "channel.h"
>  #include "file.h"
>  #include "migration.h"
>  #include "io/channel-file.h"
>  #include "io/channel-util.h"
> +#include "options.h"
>  #include "trace.h"
>  
>  #define OFFSET_OPTION ",offset="
> @@ -136,7 +138,8 @@ void file_start_incoming_migration(const char *filespec, Error **errp)
>      g_autofree char *filename = g_strdup(filespec);
>      QIOChannelFile *fioc = NULL;
>      uint64_t offset = 0;
> -    QIOChannel *ioc;
> +    int channels = 1;
> +    int i = 0, fd;
>  
>      trace_migration_file_incoming(filename);
>  
> @@ -146,16 +149,32 @@ void file_start_incoming_migration(const char *filespec, Error **errp)
>  
>      fioc = qio_channel_file_new_path(filename, O_RDONLY, 0, errp);
>      if (!fioc) {
> -        return;
> +        goto out;

Can we already return with *errp set?  Why still need the error_report()?

> +    }
> +
> +    if (migrate_multifd()) {
> +        channels += migrate_multifd_channels();
>      }
>  
> -    ioc = QIO_CHANNEL(fioc);
> -    if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
> +    fd = fioc->fd;
> +
> +    do {
> +        QIOChannel *ioc = QIO_CHANNEL(fioc);
> +
> +        if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
> +            return;
> +        }
> +
> +        qio_channel_set_name(ioc, "migration-file-incoming");
> +        qio_channel_add_watch_full(ioc, G_IO_IN,
> +                                   file_accept_incoming_migration,
> +                                   NULL, NULL,
> +                                   g_main_context_get_thread_default());
> +    } while (++i < channels && (fioc = qio_channel_file_new_fd(fd)));
> +
> +out:
> +    if (!fioc) {
> +        error_report("Error creating migration incoming channel");
>          return;
>      }
> -    qio_channel_set_name(QIO_CHANNEL(ioc), "migration-file-incoming");
> -    qio_channel_add_watch_full(ioc, G_IO_IN,
> -                               file_accept_incoming_migration,
> -                               NULL, NULL,
> -                               g_main_context_get_thread_default());
>  }
> diff --git a/migration/migration.c b/migration/migration.c
> index ba806cea55..5fa726f6d4 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -756,6 +756,8 @@ void migration_ioc_process_incoming(QIOChannel *ioc, Error **errp)
>          }
>  
>          default_channel = (channel_magic == cpu_to_be32(QEMU_VM_FILE_MAGIC));
> +    } else if (migrate_multifd() && migrate_fixed_ram()) {
> +        default_channel = multifd_recv_first_channel();

Is this check required?  IIUC you wanted to set default_channel only when
the 1st time trigger this function, but then IIUC that's exactly what:

        default_channel = !mis->from_src_file;

is about?

I think it may be clearer to add "migrate_multifd_packets()" too in the
previous "if" check to make sure fixed-ram won't peak it.

IIUC now it won't fall into that now only because file URI doesn't yet
support QIO_CHANNEL_FEATURE_READ_MSG_PEEK, however AFAIU it'll be fairly
easy to add it, and even more reasonable than a socket, when adding.

Fundamentally that trick can only work with multifd init packets, that
matches with what migrate_multifd_packets() means.

>      } else {
>          default_channel = !mis->from_src_file;
>      }
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 75a17ea8ab..ad51210f13 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -1242,6 +1242,11 @@ int multifd_load_setup(Error **errp)
>      return 0;
>  }
>  
> +bool multifd_recv_first_channel(void)
> +{
> +    return !multifd_recv_state;
> +}
> +
>  bool multifd_recv_all_channels_created(void)
>  {
>      int thread_count = migrate_multifd_channels();
> @@ -1284,7 +1289,7 @@ void multifd_recv_new_channel(QIOChannel *ioc, Error **errp)
>          /* initial packet */
>          num_packets = 1;
>      } else {
> -        id = 0;
> +        id = qatomic_read(&multifd_recv_state->count);

I was quite confused on the previous "id=0" and now it answers..

Can we merge the two patches somehow?

>      }
>  
>      p = &multifd_recv_state->params[id];
> diff --git a/migration/multifd.h b/migration/multifd.h
> index a835643b48..a112ec7ac6 100644
> --- a/migration/multifd.h
> +++ b/migration/multifd.h
> @@ -18,6 +18,7 @@ void multifd_save_cleanup(void);
>  int multifd_load_setup(Error **errp);
>  void multifd_load_cleanup(void);
>  void multifd_load_shutdown(void);
> +bool multifd_recv_first_channel(void);
>  bool multifd_recv_all_channels_created(void);
>  void multifd_recv_new_channel(QIOChannel *ioc, Error **errp);
>  void multifd_recv_sync_main(void);
> -- 
> 2.35.3
> 

-- 
Peter Xu