On 08.06.23 16:56, Eric Blake wrote:
Our code relies on a sentinel cookie value of zero for deciding when a packet has been handled, as well as relying on array indices between 0 and MAX_NBD_REQUESTS-1 for dereferencing purposes. As long as we can symmetrically convert between two forms, there is no reason to go with the odd choice of using XOR with a random pointer, when we can instead simplify the mappings with a mere offset of 1.
Should we go further and use (uint64)-1 as a sentinel cookie value, and just use index as a cookie? Or, using zero cookie in a wire looks too asymmetric?
Signed-off-by: Eric Blake <ebl...@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
--- v4: new patch --- block/nbd.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/block/nbd.c b/block/nbd.c index be3c46c6fee..5322e66166c 100644 --- a/block/nbd.c +++ b/block/nbd.c @@ -50,8 +50,8 @@ #define EN_OPTSTR ":exportname=" #define MAX_NBD_REQUESTS 16 -#define COOKIE_TO_INDEX(bs, cookie) ((cookie) ^ (uint64_t)(intptr_t)(bs)) -#define INDEX_TO_COOKIE(bs, index) ((index) ^ (uint64_t)(intptr_t)(bs))
That looked like some security trick to hide real indices. But I don't think that index of request in a list is a secret information.
+#define COOKIE_TO_INDEX(cookie) ((cookie) - 1) +#define INDEX_TO_COOKIE(index) ((index) + 1)
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