Re: [Libguestfs] [nbdkit PATCH v2 5/7] server: Allow longer NBD_OPT
On 9/28/19 3:07 PM, Richard W.M. Jones wrote:
On Fri, Sep 27, 2019 at 11:48:47PM -0500, Eric Blake wrote:
> Fixes the fact that clients could not request the maximum string
> length except with NBD_OPT_EXPORT_LEN. Updates the testsuite to
> match.
>
> Signed-off-by: Eric Blake <eblake(a)redhat.com>
> ---
> server/protocol-handshake-newstyle.c | 12 +++++++-----
> tests/test-long-name.sh | 10 ++++------
> 2 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/server/protocol-handshake-newstyle.c
b/server/protocol-handshake-newstyle.c
> index 34958360..3b5d144e 100644
> --- a/server/protocol-handshake-newstyle.c
> +++ b/server/protocol-handshake-newstyle.c
> @@ -48,7 +48,7 @@
> #define MAX_NR_OPTIONS 32
>
> /* Maximum length of any option data (bytes). */
> -#define MAX_OPTION_LENGTH 4096
> +#define MAX_OPTION_LENGTH (NBD_MAX_STRING * 4)
I may have missed it - why was * 4 chosen?
NBD_OPT_SET_META_CONTEXT allows two strings plus a few glue bytes, so
more than 8k of data from a compliant client. 16k is the next power of
2. We can bump it larger if we want, especially since 16k pales in
comparison to our 32M limit on NBD_CMD_WRITE, but for now, there is
nothing in the NBD protocol larger than NBD_OPT_SET_META_CONTEXT.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
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