Re: [Qemu-devel] [PATCH v2 14/22] nbd/client: Split out nbd_receive_one_meta_context()

["Richard W.M. Jones" <rjones@redhat.com>]

On Sat, Dec 15, 2018 at 07:53:16AM -0600, Eric Blake wrote:
> Refactor nbd_negotiate_simple_meta_context() to more closely
> resemble the pattern of nbd_receive_list(), separating the
> argument validation for one pass from the caller making a loop
> over passes. No major semantic change (although one error
> message loses the original query).  The diff may be a bit hard
> to follow due to indentation changes and handling ACK first
> rather than last.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v2: split patch into easier-to-review pieces [Rich, Vladimir]
> ---
>  nbd/client.c     | 144 +++++++++++++++++++++++++++--------------------
>  nbd/trace-events |   2 +-
>  2 files changed, 84 insertions(+), 62 deletions(-)
> 
> diff --git a/nbd/client.c b/nbd/client.c
> index 5b6b9964097..0e5a9d59dbd 100644
> --- a/nbd/client.c
> +++ b/nbd/client.c
> @@ -669,6 +669,83 @@ static int nbd_send_one_meta_context(QIOChannel *ioc,
>      return ret;
>  }
> 
> +/* nbd_receive_one_meta_context:
> + * Called in a loop to receive and trace one set/list meta context reply.
> + * Pass non-NULL @name or @id to collect results back to the caller, which
> + * must eventually call g_free().
> + * return 1 if more contexts are expected,
> + *        0 if operation is complete,
> + *        -1 with errp set for any error
> + */
> +static int nbd_receive_one_meta_context(QIOChannel *ioc,
> +                                        uint32_t opt,
> +                                        char **name,
> +                                        uint32_t *id,
> +                                        Error **errp)
> +{
> +    int ret;
> +    NBDOptionReply reply;
> +    char *local_name = NULL;
> +    uint32_t local_id;
> +
> +    if (nbd_receive_option_reply(ioc, opt, &reply, errp) < 0) {
> +        return -1;
> +    }
> +
> +    ret = nbd_handle_reply_err(ioc, &reply, errp);
> +    if (ret <= 0) {
> +        return ret;
> +    }
> +
> +    if (reply.type == NBD_REP_ACK) {
> +        if (reply.length != 0) {
> +            error_setg(errp, "Unexpected length to ACK response");
> +            nbd_send_opt_abort(ioc);
> +            return -1;
> +        }
> +        return 0;
> +    } else if (reply.type != NBD_REP_META_CONTEXT) {
> +        error_setg(errp, "Unexpected reply type %u (%s), expected %u (%s)",
> +                   reply.type, nbd_rep_lookup(reply.type),
> +                   NBD_REP_META_CONTEXT, nbd_rep_lookup(NBD_REP_META_CONTEXT));
> +        nbd_send_opt_abort(ioc);
> +        return -1;
> +    }
> +
> +    if (reply.length <= sizeof(local_id) ||
> +        reply.length > NBD_MAX_BUFFER_SIZE) {
> +        error_setg(errp, "Failed to negotiate meta context, server "
> +                   "answered with unexpected length %" PRIu32,
> +                   reply.length);
> +        nbd_send_opt_abort(ioc);
> +        return -1;
> +    }
> +
> +    if (nbd_read(ioc, &local_id, sizeof(local_id), errp) < 0) {
> +        return -1;
> +    }
> +    local_id = be32_to_cpu(local_id);
> +
> +    reply.length -= sizeof(local_id);
> +    local_name = g_malloc(reply.length + 1);
> +    if (nbd_read(ioc, local_name, reply.length, errp) < 0) {
> +        g_free(local_name);
> +        return -1;
> +    }
> +    local_name[reply.length] = '\0';
> +    trace_nbd_opt_meta_reply(nbd_opt_lookup(opt), local_name, local_id);
> +
> +    if (name) {
> +        *name = local_name;
> +    } else {
> +        g_free(local_name);
> +    }
> +    if (id) {
> +        *id = local_id;
> +    }
> +    return 1;
> +}
> +
>  /* nbd_negotiate_simple_meta_context:
>   * Request the server to set the meta context for export @info->name
>   * using @info->x_dirty_bitmap with a fallback to "base:allocation",
> @@ -690,7 +767,6 @@ static int nbd_negotiate_simple_meta_context(QIOChannel *ioc,
>       * function should lose the term _simple.
>       */
>      int ret;
> -    NBDOptionReply reply;
>      const char *context = info->x_dirty_bitmap ?: "base:allocation";
>      bool received = false;
> 
> @@ -699,44 +775,17 @@ static int nbd_negotiate_simple_meta_context(QIOChannel *ioc,
>          return -1;
>      }
> 
> -    if (nbd_receive_option_reply(ioc, NBD_OPT_SET_META_CONTEXT, &reply,
> -                                 errp) < 0)
> -    {
> -        return -1;
> -    }
> -
> -    ret = nbd_handle_reply_err(ioc, &reply, errp);
> -    if (ret <= 0) {
> -        return ret;
> -    }
> -
> -    while (reply.type == NBD_REP_META_CONTEXT) {
> +    while (1) {
>          char *name;
> 
> -        if (reply.length <= sizeof(info->context_id) ||
> -            reply.length > NBD_MAX_BUFFER_SIZE) {
> -            error_setg(errp, "Failed to negotiate meta context '%s', server "
> -                       "answered with unexpected length %" PRIu32, context,
> -                       reply.length);
> -            nbd_send_opt_abort(ioc);
> +        ret = nbd_receive_one_meta_context(ioc, NBD_OPT_SET_META_CONTEXT,
> +                                           &name, &info->context_id, errp);
> +        if (ret < 0) {
>              return -1;
> +        } else if (ret == 0) {
> +            return received;
>          }
> 
> -        if (nbd_read(ioc, &info->context_id, sizeof(info->context_id),
> -                     errp) < 0) {
> -            return -1;
> -        }
> -        info->context_id = be32_to_cpu(info->context_id);
> -
> -        reply.length -= sizeof(info->context_id);
> -        name = g_malloc(reply.length + 1);
> -        if (nbd_read(ioc, name, reply.length, errp) < 0) {
> -            g_free(name);
> -            return -1;
> -        }
> -        name[reply.length] = '\0';
> -        trace_nbd_opt_meta_reply(name, info->context_id);
> -
>          if (received) {
>              error_setg(errp, "Server replied with more than one context");
>              g_free(name);
> @@ -754,34 +803,7 @@ static int nbd_negotiate_simple_meta_context(QIOChannel *ioc,
>          }
>          g_free(name);
>          received = true;
> -
> -        /* receive NBD_REP_ACK */
> -        if (nbd_receive_option_reply(ioc, NBD_OPT_SET_META_CONTEXT, &reply,
> -                                     errp) < 0)
> -        {
> -            return -1;
> -        }
> -
> -        ret = nbd_handle_reply_err(ioc, &reply, errp);
> -        if (ret <= 0) {
> -            return ret;
> -        }
>      }
> -
> -    if (reply.type != NBD_REP_ACK) {
> -        error_setg(errp, "Unexpected reply type %u (%s), expected %u (%s)",
> -                   reply.type, nbd_rep_lookup(reply.type),
> -                   NBD_REP_ACK, nbd_rep_lookup(NBD_REP_ACK));
> -        nbd_send_opt_abort(ioc);
> -        return -1;
> -    }
> -    if (reply.length) {
> -        error_setg(errp, "Unexpected length to ACK response");
> -        nbd_send_opt_abort(ioc);
> -        return -1;
> -    }
> -
> -    return received;
>  }
> 
>  int nbd_receive_negotiate(QIOChannel *ioc, QCryptoTLSCreds *tlscreds,
> diff --git a/nbd/trace-events b/nbd/trace-events
> index 00872a6f9d4..02956c96042 100644
> --- a/nbd/trace-events
> +++ b/nbd/trace-events
> @@ -12,7 +12,7 @@ nbd_receive_query_exports_success(const char *wantname) "Found desired export na
>  nbd_receive_starttls_new_client(void) "Setting up TLS"
>  nbd_receive_starttls_tls_handshake(void) "Starting TLS handshake"
>  nbd_opt_meta_request(const char *optname, const char *context, const char *export) "Requesting %s %s for export %s"
> -nbd_opt_meta_reply(const char *context, uint32_t id) "Received mapping of context %s to id %" PRIu32
> +nbd_opt_meta_reply(const char *optname, const char *context, uint32_t id) "Received %s mapping of %s to id %" PRIu32
>  nbd_receive_negotiate(void *tlscreds, const char *hostname) "Receiving negotiation tlscreds=%p hostname=%s"
>  nbd_receive_negotiate_magic(uint64_t magic) "Magic is 0x%" PRIx64
>  nbd_receive_negotiate_server_flags(uint32_t globalflags) "Global flags are 0x%" PRIx32

So I looked at both the changes you've made and the overall effect on
the code.

I think the individual changes are correct, albeit quite convoluted to
follow because of (as you say in the commit) moving the test for
NBD_REP_ACK first and also a few conditionals which are inverted.

However importantly the overall effect on the code after the patch is
applied makes it much easier to understand than before.

Therefore:

Reviewed-by: Richard W.M. Jones <rjones@redhat.com>

Rich.

-- 
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