Re: [PATCH v4 20/34] migration/multifd: Add outgoing QIOChannelFile support

[Peter Xu <peterx@redhat.com>]

On Tue, Feb 20, 2024 at 07:41:24PM -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.
> 
> Contrary to the socket migration, the file migration doesn't need an
> asynchronous channel creation process, so expose
> multifd_channel_connect() and call it directly.
> 
> Note that this is just setup code and multifd cannot yet make use of
> the file channels.
> 
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  migration/file.c    | 40 ++++++++++++++++++++++++++++++++++++++--
>  migration/file.h    |  5 +++++
>  migration/multifd.c | 27 ++++++++++++++++++++++-----
>  migration/multifd.h |  2 ++
>  4 files changed, 67 insertions(+), 7 deletions(-)
> 
> diff --git a/migration/file.c b/migration/file.c
> index 22d052a71f..ac9f6ae40a 100644
> --- a/migration/file.c
> +++ b/migration/file.c
> @@ -12,12 +12,17 @@
>  #include "channel.h"
>  #include "file.h"
>  #include "migration.h"
> +#include "multifd.h"
>  #include "io/channel-file.h"
>  #include "io/channel-util.h"
>  #include "trace.h"
>  
>  #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)
> @@ -37,6 +42,34 @@ int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp)
>      return 0;
>  }
>  
> +int file_send_channel_destroy(QIOChannel *ioc)
> +{
> +    if (ioc) {
> +        qio_channel_close(ioc, NULL);
> +    }
> +    g_free(outgoing_args.fname);
> +    outgoing_args.fname = NULL;
> +
> +    return 0;
> +}
> +
> +bool file_send_channel_create(gpointer opaque, Error **errp)
> +{
> +    QIOChannelFile *ioc;
> +    int flags = O_WRONLY;
> +
> +    ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
> +    if (!ioc) {
> +        return false;
> +    }
> +
> +    if (!multifd_channel_connect(opaque, QIO_CHANNEL(ioc), errp)) {
> +        return false;
> +    }
> +
> +    return true;
> +}
> +
>  void file_start_outgoing_migration(MigrationState *s,
>                                     FileMigrationArgs *file_args, Error **errp)
>  {
> @@ -44,15 +77,18 @@ 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);

This change seems irrelevant, could be squashed into the previous patch
when introduced?

>      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..90794b494b 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);
> +
> +bool file_send_channel_create(gpointer opaque, Error **errp);
> +int file_send_channel_destroy(QIOChannel *ioc);
>  #endif
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 45a0c7aaa8..507b497d52 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"
>  
> @@ -680,6 +682,9 @@ static void multifd_send_terminate_threads(void)
>  
>  static int multifd_send_channel_destroy(QIOChannel *send)
>  {
> +    if (!multifd_use_packets()) {
> +        return file_send_channel_destroy(send);
> +    }
>      return socket_send_channel_destroy(send);
>  }
>  
> @@ -959,9 +964,8 @@ static bool multifd_tls_channel_connect(MultiFDSendParams *p,
>      return true;
>  }
>  
> -static bool multifd_channel_connect(MultiFDSendParams *p,
> -                                    QIOChannel *ioc,
> -                                    Error **errp)
> +bool multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc,
> +                             Error **errp)
>  {
>      qio_channel_set_delay(ioc, false);
>  
> @@ -1031,9 +1035,14 @@ out:
>      error_free(local_err);
>  }
>  
> -static void multifd_new_send_channel_create(gpointer opaque)
> +static bool multifd_new_send_channel_create(gpointer opaque, Error **errp)
>  {
> +    if (!multifd_use_packets()) {
> +        return file_send_channel_create(opaque, errp);
> +    }
> +
>      socket_send_channel_create(multifd_new_send_channel_async, opaque);
> +    return true;
>  }
>  
>  bool multifd_send_setup(void)
> @@ -1082,7 +1091,15 @@ bool multifd_send_setup(void)
>          p->page_size = qemu_target_page_size();
>          p->page_count = page_count;
>          p->write_flags = 0;
> -        multifd_new_send_channel_create(p);
> +
> +        if (!multifd_new_send_channel_create(p, &local_err)) {
> +            /*
> +             * File channel creation is synchronous, we don't need the
> +             * semaphore below, it's safe to return now.
> +             */
> +            assert(migrate_fixed_ram());

This comment and assert() is slightly confusing to me.  Drop them?

IMHO it's always safe to directly return here, the channels_created sem
will be destroyed later anyway so the number shouldn't matter.

And as I commented in the other email, IMHO it's cleaner we also post that
sem in file_send_channel_create().

> +            return -1;
> +        }
>      }
>  
>      if (use_packets) {
> diff --git a/migration/multifd.h b/migration/multifd.h
> index 19188815a3..135f6ed098 100644
> --- a/migration/multifd.h
> +++ b/migration/multifd.h
> @@ -228,5 +228,7 @@ static inline void multifd_send_prepare_header(MultiFDSendParams *p)
>      p->iovs_num++;
>  }
>  
> +bool multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc,
> +                             Error **errp);
>  
>  #endif
> -- 
> 2.35.3
> 

-- 
Peter Xu