Re: [Qemu-devel] [RFC PATCH 1/2] migration: Allow the migrate command to work on file:urls

["Daniel P. Berrange" <berrange@redhat.com>]

On Thu, Jul 21, 2016 at 01:05:59PM +0800, zhanghailiang wrote:
> Usage:
> (qemu) migrate file:/path/to/vm_statefile
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Benoit Canet <benoit.canet@gmail.com>
> ---
>  include/migration/migration.h |  2 ++
>  migration/fd.c                | 34 ++++++++++++++++++++++++++++------
>  migration/migration.c         |  2 ++
>  migration/trace-events        |  1 +
>  4 files changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index 3c96623..cc2e4f6 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -221,6 +221,8 @@ void fd_start_incoming_migration(const char *path, Error **errp);
>  
>  void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp);
>  
> +void file_start_outgoing_migration(MigrationState *s, const char *filename, Error **errp);
> +
>  void rdma_start_outgoing_migration(void *opaque, const char *host_port, Error **errp);
>  
>  void rdma_start_incoming_migration(const char *host_port, Error **errp);
> diff --git a/migration/fd.c b/migration/fd.c
> index 84a10fd..fa5df67 100644
> --- a/migration/fd.c
> +++ b/migration/fd.c
> @@ -23,15 +23,11 @@
>  #include "trace.h"
>  
>  
> -void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
> +static void fd_start_outgoing_migration_core(MigrationState *s, int fd,
> +                                             Error **errp)
>  {
>      QIOChannel *ioc;
> -    int fd = monitor_get_fd(cur_mon, fdname, errp);
> -    if (fd == -1) {
> -        return;
> -    }
>  
> -    trace_migration_fd_outgoing(fd);
>      ioc = qio_channel_new_fd(fd, errp);
>      if (!ioc) {
>          close(fd);
> @@ -42,6 +38,32 @@ void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **
>      object_unref(OBJECT(ioc));
>  }
>  
> +void fd_start_outgoing_migration(MigrationState *s, const char *fdname, Error **errp)
> +{
> +    int fd = monitor_get_fd(cur_mon, fdname, errp);
> +    if (fd == -1) {
> +        return;
> +    }
> +
> +    trace_migration_fd_outgoing(fd);
> +    fd_start_outgoing_migration_core(s, fd, errp);
> +}
> +
> +void file_start_outgoing_migration(MigrationState *s, const char *filename,
> +                                   Error **errp)
> +{
> +    int fd;
> +
> +    fd = qemu_open(filename, O_CREAT | O_TRUNC | O_WRONLY, S_IRUSR | S_IWUSR);
> +    if (fd < 0) {
> +        error_setg_errno(errp, errno, "Failed to open file: %s", filename);
> +        return;
> +    }
> +    
> +    trace_migration_file_outgoing(filename);
> +    fd_start_outgoing_migration_core(s, fd, errp);
> +}

This isn't going to fly.

Annoyingly with plain files on POSIX platforms you can't get non-blocking
I/O, so even though we'll be setting the O_NONBLOCK on fd shortly, I/O is
still going to block the entire thread.  The same applies for file reads
wrt to your next patch supporting incoming mode.

Regards,
Daniel
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