Re: [Qemu-devel] [PATCH v2 5/6] nbd/server: Add helper functions for parsing option payload

[Vladimir Sementsov-Ogievskiy]

11.01.2018 02:08, Eric Blake wrote:
> Rather than making every callsite perform length sanity checks
> and error reporting, add the helper functions nbd_opt_read()
> and nbd_opt_drop() that use the length stored in the client
> struct; also add an assertion that optlen is reduced to zero
> after each option is handled.
>
> Note that the call in nbd_negotiate_handle_export_name() does
> not use the new helper (in part because the server cannot
> reply to NBD_OPT_EXPORT_NAME - it either succeeds or the
> connection drops).
>
> Based on patches by Vladimir Sementsov-Ogievskiy.
>
> Signed-off-by: Eric Blake <address@hidden>
> ---
>   nbd/server.c | 123 ++++++++++++++++++++++++++++++-----------------------------
>   1 file changed, 63 insertions(+), 60 deletions(-)
>
> diff --git a/nbd/server.c b/nbd/server.c
> index d23bc2918a..ec8c3be019 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -229,6 +229,41 @@ nbd_negotiate_send_rep_err(NBDClient *client, uint32_t 
> type,
>       return ret;
>   }
>
> +/* Drop remainder of the current option, after sending a reply with

looks a bit weird: actually you drop the remainder _before_ sending a reply)

> + * the given error type and message. Return -errno on read or write

also, unrelated note, -errno is always forced to -EIO, because of 
nbd_read realization.
and this note applies to many other places here. It is correct (EIO is 
errno, why not?),
but it may be not bad to note it somewhere..

> + * failure; or 0 if connection is still live. */
> +static int GCC_FMT_ATTR(4, 5)
> +nbd_opt_drop(NBDClient *client, uint32_t type, Error **errp,
> +             const char *fmt, ...)
> +{
> +    int ret = nbd_drop(client->ioc, client->optlen, errp);
> +
> +    client->optlen = 0;
> +    if (!ret) {
> +        va_list va;
> +
> +        va_start(va, fmt);
> +        ret = nbd_negotiate_send_rep_verr(client, type, errp, fmt, va);
> +        va_end(va);
> +    }
> +    return ret;
> +}

[..]

> @@ -812,14 +819,9 @@ static int nbd_negotiate_options(NBDClient *client, 
> uint16_t myflags,
>                   break;
>
>               default:
> -                if (nbd_drop(client->ioc, length, errp) < 0) {
> -                    return -EIO;
> -                }
> -                ret = nbd_negotiate_send_rep_err(client,
> -                                                 NBD_REP_ERR_UNSUP, errp,
> -                                                 "Unsupported option 0x%"
> -                                                 PRIx32 " (%s)", option,
> -                                                 nbd_opt_lookup(option));
> +                ret = nbd_opt_drop(client, NBD_REP_ERR_UNSUP, errp,
> +                                   "Unsupported option 0x%" PRIx32 " (%s)",
> +                                   option, nbd_opt_lookup(option));
>                   break;
>               }
>           } else {
> @@ -842,6 +844,7 @@ static int nbd_negotiate_options(NBDClient *client, 
> uint16_t myflags,
>           if (ret < 0) {
>               return ret;
>           }
> +        assert(!client->optlen);

isn't it from 2/6?

>       }
>   }

anyway,

Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

--
Best regards,
Vladimir