Re: [PATCH v2 01/11] migration: support file: uri for source migration

[Daniel P . Berrangé]

On Mon, Oct 10, 2022 at 04:33:58PM +0300, Nikolay Borisov wrote:
> Implement support for a "file:" uri so that a migration can be initiated
> directly to a file from QEMU.

Can we add a reminder here

  Unlike other migration protocol backends, the 'file' protocol cannot
  honour non-blocking mode. POSIX file/block storage will always report
  ready to read/write, regardless of how slow the underlying storage
  will be at servicing the request.

  For outgoing migration this limitation is not a serious problem as
  the migration data transfer always happens in a dedicated thread.
  It may, however, result in delays in honouring a request to cancel
  the migration operation.

> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  migration/file.c      | 23 +++++++++++++++++++++++
>  migration/file.h      |  9 +++++++++
>  migration/meson.build |  1 +
>  migration/migration.c |  3 +++
>  4 files changed, 36 insertions(+)
>  create mode 100644 migration/file.c
>  create mode 100644 migration/file.h
> 
> diff --git a/migration/file.c b/migration/file.c
> new file mode 100644
> index 000000000000..02896a7cab99
> --- /dev/null
> +++ b/migration/file.c
> @@ -0,0 +1,23 @@
> +#include "qemu/osdep.h"
> +#include "channel.h"
> +#include "io/channel-file.h"
> +#include "file.h"
> +#include "qemu/error-report.h"
> +
> +
> +void file_start_outgoing_migration(MigrationState *s, const char *fname, 
> Error **errp)
> +{
> +     QIOChannelFile *ioc;
> +
> +     ioc = qio_channel_file_new_path(fname, O_CREAT|O_TRUNC|O_WRONLY, 0660, 
> errp);
> +     if (!ioc) {
> +             error_report("Error creating a channel");
> +             return;
> +     }
> +
> +     qio_channel_set_name(QIO_CHANNEL(ioc), "migration-file-outgoing");
> +     migration_channel_connect(s, QIO_CHANNEL(ioc), NULL, NULL);
> +     object_unref(OBJECT(ioc));
> +}
> +
> +
> diff --git a/migration/file.h b/migration/file.h
> new file mode 100644
> index 000000000000..d476eb1157f9
> --- /dev/null
> +++ b/migration/file.h
> @@ -0,0 +1,9 @@
> +#ifndef QEMU_MIGRATION_FILE_H
> +#define QEMU_MIGRATION_FILE_H
> +
> +void file_start_outgoing_migration(MigrationState *s,
> +                                   const char *filename,
> +                                   Error **errp);
> +
> +#endif
> +
> diff --git a/migration/meson.build b/migration/meson.build
> index 690487cf1a81..30a8392701c3 100644
> --- a/migration/meson.build
> +++ b/migration/meson.build
> @@ -17,6 +17,7 @@ softmmu_ss.add(files(
>    'colo.c',
>    'exec.c',
>    'fd.c',
> +  'file.c',
>    'global_state.c',
>    'migration.c',
>    'multifd.c',
> diff --git a/migration/migration.c b/migration/migration.c
> index bb8bbddfe467..8813b78b9a6b 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -20,6 +20,7 @@
>  #include "migration/blocker.h"
>  #include "exec.h"
>  #include "fd.h"
> +#include "file.h"
>  #include "socket.h"
>  #include "sysemu/runstate.h"
>  #include "sysemu/sysemu.h"
> @@ -2414,6 +2415,8 @@ void qmp_migrate(const char *uri, bool has_blk, bool 
> blk,
>          exec_start_outgoing_migration(s, p, &local_err);
>      } else if (strstart(uri, "fd:", &p)) {
>          fd_start_outgoing_migration(s, p, &local_err);
> +    } else if (strstart(uri, "file:", &p)) {
> +     file_start_outgoing_migration(s, p, &local_err);
>      } else {
>          if (!(has_resume && resume)) {
>              yank_unregister_instance(MIGRATION_YANK_INSTANCE);
> -- 
> 2.34.1
> 

With regards,
Daniel
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