Re: [Qemu-devel] [PATCH v5 05/14] nbd: Share common reply-sending code in server

[Fam Zheng <famz@redhat.com>]

On Mon, 07/18 22:07, Eric Blake wrote:
> Rather than open-coding NBD_REP_SERVER, reuse the code we
> already have by adding a length parameter.  Additionally,
> the refactoring will make adding NBD_OPT_GO in a later patch
> easier.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v4: no change
> v3: rebase to changes earlier in series
> ---
>  nbd/server.c | 48 +++++++++++++++++++++++-------------------------
>  1 file changed, 23 insertions(+), 25 deletions(-)
> 
> diff --git a/nbd/server.c b/nbd/server.c
> index 85c4f5d..c8716f1 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -195,12 +195,15 @@ static ssize_t nbd_negotiate_drop_sync(QIOChannel *ioc, size_t size)
> 
>  */
> 
> -static int nbd_negotiate_send_rep(QIOChannel *ioc, uint32_t type, uint32_t opt)
> +/* Send a reply header, including length, but no payload.
> + * Return -errno to kill connection, 0 to continue negotiation. */

Not a show stopper but I'm not sure documenting the control logic of the
outermost caller a few layers away is a good idea, the same question applies to
functions below as well.

> +static int nbd_negotiate_send_rep_len(QIOChannel *ioc, uint32_t type,
> +                                      uint32_t opt, uint32_t len)
>  {
>      uint64_t magic;
> -    uint32_t len;
> 
> -    TRACE("Reply opt=%" PRIx32 " type=%" PRIx32, type, opt);
> +    TRACE("Reply opt=%" PRIx32 " type=%" PRIx32 " len=%" PRIu32,
> +          type, opt, len);
> 
>      magic = cpu_to_be64(NBD_REP_MAGIC);
>      if (nbd_negotiate_write(ioc, &magic, sizeof(magic)) != sizeof(magic)) {
> @@ -217,7 +220,7 @@ static int nbd_negotiate_send_rep(QIOChannel *ioc, uint32_t type, uint32_t opt)
>          LOG("write failed (rep type)");
>          return -EINVAL;
>      }
> -    len = cpu_to_be32(0);
> +    len = cpu_to_be32(len);
>      if (nbd_negotiate_write(ioc, &len, sizeof(len)) != sizeof(len)) {
>          LOG("write failed (rep data length)");
>          return -EINVAL;
> @@ -225,37 +228,32 @@ static int nbd_negotiate_send_rep(QIOChannel *ioc, uint32_t type, uint32_t opt)
>      return 0;
>  }
> 
> +/* Send a reply header with default 0 length.
> + * Return -errno to kill connection, 0 to continue negotiation. */
> +static int nbd_negotiate_send_rep(QIOChannel *ioc, uint32_t type, uint32_t opt)
> +{
> +    return nbd_negotiate_send_rep_len(ioc, type, opt, 0);
> +}
> +
> +/* Send an NBD_REP_SERVER reply to NBD_OPT_LIST, including payload.
> + * Return -errno to kill connection, 0 to continue negotiation. */
>  static int nbd_negotiate_send_rep_list(QIOChannel *ioc, NBDExport *exp)
>  {
> -    uint64_t magic;
>      size_t name_len, desc_len;
> -    uint32_t opt, type, len;
> +    uint32_t len;
>      const char *name = exp->name ? exp->name : "";
>      const char *desc = exp->description ? exp->description : "";
> +    int rc;
> 
>      TRACE("Advertising export name '%s' description '%s'", name, desc);
>      name_len = strlen(name);
>      desc_len = strlen(desc);
> -    magic = cpu_to_be64(NBD_REP_MAGIC);
> -    if (nbd_negotiate_write(ioc, &magic, sizeof(magic)) != sizeof(magic)) {
> -        LOG("write failed (magic)");
> -        return -EINVAL;
> -     }
> -    opt = cpu_to_be32(NBD_OPT_LIST);
> -    if (nbd_negotiate_write(ioc, &opt, sizeof(opt)) != sizeof(opt)) {
> -        LOG("write failed (opt)");
> -        return -EINVAL;
> -    }
> -    type = cpu_to_be32(NBD_REP_SERVER);
> -    if (nbd_negotiate_write(ioc, &type, sizeof(type)) != sizeof(type)) {
> -        LOG("write failed (reply type)");
> -        return -EINVAL;
> -    }
> -    len = cpu_to_be32(name_len + desc_len + sizeof(len));
> -    if (nbd_negotiate_write(ioc, &len, sizeof(len)) != sizeof(len)) {
> -        LOG("write failed (length)");
> -        return -EINVAL;
> +    len = name_len + desc_len + sizeof(len);
> +    rc = nbd_negotiate_send_rep_len(ioc, NBD_REP_SERVER, NBD_OPT_LIST, len);
> +    if (rc < 0) {
> +        return rc;
>      }
> +
>      len = cpu_to_be32(name_len);
>      if (nbd_negotiate_write(ioc, &len, sizeof(len)) != sizeof(len)) {
>          LOG("write failed (name length)");
> -- 
> 2.5.5
> 
>