Re: [Qemu-devel] [PATCH v2 13/22] nbd/client: Split out nbd_send_one_meta_context()

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

On Sat, Dec 15, 2018 at 07:53:15AM -0600, Eric Blake wrote:
> Refactor nbd_negotiate_simple_meta_context() to pull out the
> code that can be reused to send a LIST request for 0 or 1 query.
> No semantic change.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v2: split patch into easier-to-review pieces [Rich, Vladimir]
> ---
>  nbd/client.c     | 64 ++++++++++++++++++++++++++++++++++--------------
>  nbd/trace-events |  2 +-
>  2 files changed, 46 insertions(+), 20 deletions(-)
> 
> diff --git a/nbd/client.c b/nbd/client.c
> index b6a85fc3ef8..5b6b9964097 100644
> --- a/nbd/client.c
> +++ b/nbd/client.c
> @@ -627,6 +627,48 @@ static QIOChannel *nbd_receive_starttls(QIOChannel *ioc,
>      return QIO_CHANNEL(tioc);
>  }
> 
> +/* nbd_send_one_meta_context:
> + * Send 0 or 1 set/list meta context queries.
> + * return 0 on success, -1 with errp set for any error
> + */
> +static int nbd_send_one_meta_context(QIOChannel *ioc,
> +                                     uint32_t opt,
> +                                     const char *export,
> +                                     const char *query,
> +                                     Error **errp)
> +{
> +    int ret;
> +    uint32_t export_len = strlen(export);
> +    uint32_t queries = !!query;
> +    uint32_t context_len = 0;
> +    uint32_t data_len;
> +    char *data;
> +    char *p;
> +
> +    data_len = sizeof(export_len) + export_len + sizeof(queries);
> +    if (query) {
> +        context_len = strlen(query);
> +        data_len += sizeof(context_len) + context_len;
> +    } else {
> +        assert(opt == NBD_OPT_LIST_META_CONTEXT);
> +    }
> +    data = g_malloc(data_len);
> +    p = data;
> +
> +    trace_nbd_opt_meta_request(nbd_opt_lookup(opt), query ?: "(all)", export);
> +    stl_be_p(p, export_len);
> +    memcpy(p += sizeof(export_len), export, export_len);
> +    stl_be_p(p += export_len, queries);
> +    if (query) {
> +        stl_be_p(p += sizeof(uint32_t), context_len);
> +        memcpy(p += sizeof(context_len), query, context_len);
> +    }
> +
> +    ret = nbd_send_option_request(ioc, opt, data_len, data, errp);
> +    g_free(data);
> +    return ret;
> +}
> +
>  /* 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",
> @@ -651,26 +693,10 @@ static int nbd_negotiate_simple_meta_context(QIOChannel *ioc,
>      NBDOptionReply reply;
>      const char *context = info->x_dirty_bitmap ?: "base:allocation";
>      bool received = false;
> -    uint32_t export_len = strlen(info->name);
> -    uint32_t context_len = strlen(context);
> -    uint32_t data_len = sizeof(export_len) + export_len +
> -                        sizeof(uint32_t) + /* number of queries */
> -                        sizeof(context_len) + context_len;
> -    char *data = g_malloc(data_len);
> -    char *p = data;
> 
> -    trace_nbd_opt_meta_request(context, info->name);
> -    stl_be_p(p, export_len);
> -    memcpy(p += sizeof(export_len), info->name, export_len);
> -    stl_be_p(p += export_len, 1);
> -    stl_be_p(p += sizeof(uint32_t), context_len);
> -    memcpy(p += sizeof(context_len), context, context_len);
> -
> -    ret = nbd_send_option_request(ioc, NBD_OPT_SET_META_CONTEXT, data_len, data,
> -                                  errp);
> -    g_free(data);
> -    if (ret < 0) {
> -        return ret;
> +    if (nbd_send_one_meta_context(ioc, NBD_OPT_SET_META_CONTEXT,
> +                                  info->name, context, errp) < 0) {
> +        return -1;
>      }
> 
>      if (nbd_receive_option_reply(ioc, NBD_OPT_SET_META_CONTEXT, &reply,
> diff --git a/nbd/trace-events b/nbd/trace-events
> index 446d10b8603..00872a6f9d4 100644
> --- a/nbd/trace-events
> +++ b/nbd/trace-events
> @@ -11,7 +11,7 @@ nbd_receive_query_exports_start(const char *wantname) "Querying export list for
>  nbd_receive_query_exports_success(const char *wantname) "Found desired export name '%s'"
>  nbd_receive_starttls_new_client(void) "Setting up TLS"
>  nbd_receive_starttls_tls_handshake(void) "Starting TLS handshake"
> -nbd_opt_meta_request(const char *context, const char *export) "Requesting to set meta context %s for export %s"
> +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_receive_negotiate(void *tlscreds, const char *hostname) "Receiving negotiation tlscreds=%p hostname=%s"
>  nbd_receive_negotiate_magic(uint64_t magic) "Magic is 0x%" PRIx64

Although a straightforward refactoring, we still lost the comment
/* number of queries */.  I'd still perhaps like to see a bit more
explanation of the layout and reasoning behind the data buffer.
But anyway ..

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

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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