Re: [Qemu-devel] [PATCH 05/18] migration: avoid using error_is_set

[Luiz Capitulino <lcapitulino@redhat.com>]

On Wed,  3 Oct 2012 16:36:52 +0200
Paolo Bonzini <pbonzini@redhat.com> wrote:

> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

The patch's description is a bit misleading. The real problem this fixes
is that the migration code is using errp to detect "internal" errors,
this means that it relies on errp being non-NULL.

There's no problem using error_set(). Actually, I do prefer using it, because
at least in theory we shouldn't assume the Error object to have this
particular semantic.

One more comment below.

> ---
>  migration-tcp.c |  8 +++++---
>  migration.c     | 13 +++++++------
>  2 file modificati, 12 inserzioni(+), 9 rimozioni(-)
> 
> diff --git a/migration-tcp.c b/migration-tcp.c
> index a15c2b8..78337a3 100644
> --- a/migration-tcp.c
> +++ b/migration-tcp.c
> @@ -71,14 +71,16 @@ static void tcp_wait_for_connect(int fd, void *opaque)
>  int tcp_start_outgoing_migration(MigrationState *s, const char *host_port,
>                                   Error **errp)
>  {
> +    Error *local_err = NULL;
> +
>      s->get_error = socket_errno;
>      s->write = socket_write;
>      s->close = tcp_close;
>  
> -    s->fd = inet_nonblocking_connect(host_port, tcp_wait_for_connect, s,
> -                                     errp);
> -    if (error_is_set(errp)) {
> +    s->fd = inet_nonblocking_connect(host_port, tcp_wait_for_connect, s, &local_err);
> +    if (local_err != NULL) {
>          migrate_fd_error(s);
> +        error_propagate(errp, local_err);
>          return -1;
>      }
>  
> diff --git a/migration.c b/migration.c
> index 22a05c4..8a04174 100644
> --- a/migration.c
> +++ b/migration.c
> @@ -481,6 +481,7 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
>                   bool has_inc, bool inc, bool has_detach, bool detach,
>                   Error **errp)
>  {
> +    Error *local_err = NULL;
>      MigrationState *s = migrate_get_current();
>      MigrationParams params;
>      const char *p;
> @@ -506,7 +507,7 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
>      s = migrate_init(&params);
>  
>      if (strstart(uri, "tcp:", &p)) {
> -        ret = tcp_start_outgoing_migration(s, p, errp);
> +        ret = tcp_start_outgoing_migration(s, p, &local_err);
>  #if !defined(WIN32)
>      } else if (strstart(uri, "exec:", &p)) {
>          ret = exec_start_outgoing_migration(s, p);
> @@ -520,11 +521,11 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
>          return;
>      }
>  
> -    if (ret < 0) {
> -        if (!error_is_set(errp)) {
> -            DPRINTF("migration failed: %s\n", strerror(-ret));
> -            /* FIXME: we should return meaningful errors */
> -            error_set(errp, QERR_UNDEFINED_ERROR);
> +    if (ret < 0 || local_err) {
> +        if (!local_err) {
> +            error_set_errno(errp, -ret, QERR_UNDEFINED_ERROR);

Two problems here. First, ret usually is not -errno. If we really want to
use it here (I think this is great improvement) than we have to fix the
functions called by qmp_migrate() first.

The other problem is just this will produce a weird error message, it's
better to do s/QERR_UNDEFINED_ERROR/"migration has failed".

> +        } else {
> +            error_propagate(errp, local_err);
>          }
>          return;
>      }