From: Luigi Mantellini <luigi.mantell...@gmail.com>
The PortId is defined as a couple of ClockId (an 8-bytes opaque) and the
PortNumber (UInterger16).
The current implementation compares the entire PortId, consisting of ClockId
and PortNumber, using a byte-to-byte comparison (memcmp).
This way doesn't consider the HOST's endianess on PortId part, giving wrong
results in same case.
Consider the following setup (assuming the same ClockId)
PortId_a = (ClockId, PortNumber=0x1234)
PortId_b = (ClockId, PortNumber=0x4512)
On a LittleEndian HOST, we obtain the following memory setup:
PortId_a = ... ClockId ... 0x34 0x12
PortId_b = ... ClockId ... 0x12 0x45
Using just a memcmp() call we obtain the WRONG result PortId_a > PortId_b,
because the byte-to-byte comparison will check the PortNumber Lower-Byte (0x34
vs 0x12) first.
To fix the BCMA implementation we need to split the PortId comparison in:
- ClockId comparison, still using memcmp() on a opaque byte stream
- PortNumber, using a natural semantic comparison between integer numbers.
In other hands, following the ITU-T G.8275.2 Figure 4, we need to ensure the
same ordering criteria on all places:
a Compare portIdentities of receiver of A and sender of A
b Compare portIdentities of receiver of B and sender of B
c Compare portIdentities of sender of A and sender of B
d Compare PortNumbers of receiver of A and receiver B
Signed-off-by: Luigi Mantellini <luigi.mantell...@gmail.com>
Signed-off-by: Luigi Mantellini <luigi.mantell...@sm-optics.com>
---
bmc.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/bmc.c b/bmc.c
index 6ac7aa0..ebc0789 100644
--- a/bmc.c
+++ b/bmc.c
@@ -21,6 +21,17 @@
#include "bmc.h"
#include "ds.h"
+static int portid_cmp(struct PortIdentity *a, struct PortIdentity *b)
+{
+ int diff = memcmp(&a->clockIdentity, &b->clockIdentity,
sizeof(a->clockIdentity));
+
+ if (diff == 0) {
+ diff = a->portNumber - b->portNumber;
+ }
+
+ return diff;
+}
+
int dscmp2(struct dataset *a, struct dataset *b)
{
int diff;
@@ -35,7 +46,7 @@ int dscmp2(struct dataset *a, struct dataset *b)
* standard, since there is nothing we can do about it anyway.
*/
if (A < B) {
- diff = memcmp(&b->receiver, &b->sender, sizeof(b->receiver));
+ diff = portid_cmp(&b->receiver, &b->sender);
if (diff < 0)
return A_BETTER;
if (diff > 0)
@@ -44,7 +55,7 @@ int dscmp2(struct dataset *a, struct dataset *b)
return 0;
}
if (A > B) {
- diff = memcmp(&a->receiver, &a->sender, sizeof(a->receiver));
+ diff = portid_cmp(&a->receiver, &a->sender);
if (diff < 0)
return B_BETTER;
if (diff > 0)
@@ -53,7 +64,7 @@ int dscmp2(struct dataset *a, struct dataset *b)
return 0;
}
- diff = memcmp(&a->sender, &b->sender, sizeof(a->sender));
+ diff = portid_cmp(&a->sender, &b->sender);
if (diff < 0)
return A_BETTER_TOPO;
if (diff > 0)
--
2.38.1
_______________________________________________
Linuxptp-devel mailing list
Linuxptp-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
