Re: [Libguestfs] [PATCH v4 06/24] nbd/client: Simplify cookie vs. index computation
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 <eblake(a)redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov(a)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)
[..]
--
Best regards,
Vladimir