On Tue, 2013-09-10 at 15:43 +0200, Lukas Slebodnik wrote:
On (10/09/13 09:18), Simo Sorce wrote:
>On Tue, 2013-09-10 at 12:24 +0200, Lukas Slebodnik wrote:
>> On (09/09/13 09:22), Simo Sorce wrote:
>> >On Mon, 2013-09-09 at 13:37 +0200, Lukas Slebodnik wrote:
>> >> On (07/09/13 13:43), Simo Sorce wrote:
>> >> >On Fri, 2013-09-06 at 18:55 -0400, Simo Sorce wrote:
>> >> >> On Fri, 2013-09-06 at 19:45 +0200, Lukas Slebodnik wrote:
>> >> >> > On (06/09/13 12:48), Simo Sorce wrote:
>> >> >> > >On Fri, 2013-09-06 at 16:26 +0200, Lukas Slebodnik
wrote:
>> >> >> > >> Step 6) Remove record R3(hash_1:4, hash_2:3)
stored at slot index 0x43
>> >> >> > >> a) Remove record R3 from chain starting by
hash R3->hash1 (value 4)
>> >> >> > >> hash[1] -> 0x12(R1) -> 0x43(R3) ->
0x54(R4) -> MC_INVALID_VAL
>> >> >> > >> hash[2] -> 0x12(R1) -> 0x43(R3) ->
0x54(R4) -> MC_INVALID_VAL
>> >> >> > >> hash[3] -> 0x43(R3) -> 0x54(R4) ->
MC_INVALID_VAL
>> >> >> > >> hash[4] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > >> hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > >>
>> >> >> > >> b) Remove record R3 from chain starting by
hash R3->hash2 (value 3)
>> >> >> > >> hash[1] -> 0x12(R1) -> 0x43(R3) ->
0x54(R4) -> MC_INVALID_VAL
>> >> >> > >> hash[2] -> 0x12(R1) -> 0x43(R3) ->
0x54(R4) -> MC_INVALID_VAL
>> >> >> > >> hash[3] -> MC_INVALID_VAL
>> >> >> > >> hash[4] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > >> hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > >>
>> >> >> > >>
>> >> >> > >I do not see how this happens, in hash[3] you have
another record after
>> >> >> > >R3 so hash[3] should be
>> >> >> > This behaviour was introduced by patch
4662725ffef62b3b2502481438effa7c8fef9f80
>> >> >> > and it is very similar to reinvalidation.
>> >> >> > >
>> >> >> > >hash[3] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > >
>> >> >> > >however I do see how R3 would remain in hash[1] and
hash[2].
>> >> >> > >
>> >> >> > >And that is a problem, the problem I was trying to
wrap my mind around
>> >> >> > >with the patch you proposed last time. Wouldn't
the revalidation idea I
>> >> >> > >had last time fix this issue ?
>> >> >> > >
>> >> >> > >Simo.
>> >> >> > >
>> >> >> >
>> >> >> > record R1(hash_1:1, hash_2:2) stored at slot index 0x12
>> >> >> > record R2(hash_1:3, hash_2:1) stored at slot index 0x31
>> >> >> > record R3(hash_1:4, hash_2:3) stored at slot index 0x43
>> >> >> > record R4(hash_1:5, hash_2:4) stored at slot index 0x54
>> >> >> >
>> >> >> > Last state:
>> >> >> > -------------------------
>> >> >> > hash[1] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >> > hash[2] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >> > hash[3] -> 0x43(R3) -> 0x54(R4) ->
MC_INVALID_VAL
>> >> >> > hash[4] -> 0x43(R3) -> 0x54(R4) ->
MC_INVALID_VAL
>> >> >> > hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> >
>> >> >> > I will try to describe last removing with your idea about
reinvalidation.
>> >> >> >
>> >> >> > Step 6) Remove record R3(hash_1:4, hash_2:3) stored at
slot index 0x43
>> >> >> > a) Remove record R3 from the 1st chain starting by
hash R3->hash1 (value 4)
>> >> >> > hash[1] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >> > hash[2] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >> > hash[3] -> 0x43(R3) -> 0x54(R4) ->
MC_INVALID_VAL
>> >> >> > hash[4] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> >
>> >> >> > b) Revalidate chain for R3->hash1 (value 4)
>> >> >> > -- chain for hash[4] refers to 0x54(R4) and R4 has
hash with value 4
>> >> >> >
>> >> >> > c) Remove record R3 from the 2nd chain starting by
hash R3->hash2 (value 3)
>> >> >> > hash[1] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >> > hash[2] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >> > hash[3] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > hash[4] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> >
>> >> >> > d) Revalidate chain for R3->hash2 (value 3)
>> >> >> > -- chain for hash[3] refers to 0x54(R4)
>> >> >> > and R4 *DOES NOT have* hash with value 4
>> >> >> > --hash[3] will refer wo successor of R4,
MC_INVALID_VAL
>> >> >> > hash[1] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >> > hash[2] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >> > hash[3] -> MC_INVALID_VAL
>> >> >> > hash[4] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> >
>> >> >> > e) Revalidate all succesors of record R3. R3->next
== 0x54 (R4)
>> >> >> > in this case, only record R4(hash_1:5, hash_2:4)
is in chain
>> >> >> > -- chain for hash[5] refers to 0x54(R4) and R4 has
hash with value 5
>> >> >> > -- chain for hash[4] refers to 0x54(R4) and R4 has
hash with value 4
>> >> >> >
>> >> >> > f) slots for record R2 will be invalidated.
>> >> >> > hash[1] -> 0x12(R1) -> INVALIDATED_SLOT ??->
0x54(R4) -> MC_INVALID_VAL
>> >> >> > hash[2] -> 0x12(R1) -> INVALIDATED_SLOT ??->
0x54(R4) -> MC_INVALID_VAL
>> >> >> > hash[3] -> MC_INVALID_VAL
>> >> >> > hash[4] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> > hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >> >
>> >> >> > As you can see the, result is the same as from my
previous mail.
>> >> >> >
>> >> >> > This is a special case, but it can happen.
>> >> >> > I spent a lot of time with reproducing this case and with
analysis.
>> >> >> > So I hope this explanation helps to understand this
special case.
>> >> >> > Is it clear now?
>> >> >>
>> >> >> It is clear to me, but what you describe here is not my
original
>> >> >> proposal.
>> >> >>
>> >> >> Revalidation was the rechecking of chains when you remove an
object.
>> >> >> In your example revalidation of the chains when you remove R2
(not R3)
>> >> >> would lead to removal of R3 from hash[1] and hash[2] chains
resolving
>> >> >> the problem.
>> >> >>
>> >> >> I am only sorry I wasn't more firm on the revalidation
idea now.
>> >> >>
>> >> >> I will send some examples later.
>> >> >>
>> >> >> Simo.
>> >> >>
>> >> >
>> >> >Just a refresher of my original proposal:
>> >> >After we remove a record we re-validate the 2 chains it belonged
to, and
>> >> >prune any record that does not match the chain record or any of
the
>> >> >chains referenced by the records that precede.
>> >> >
>> >> >
>> >> >Ok here is the example.
>> >> >
>> >> >---
>> >> >This was the problem:
>> >> >Add record R1(hash_1:1, hash_2:2) stored at slot index 0x12
>> >> >Add record R2(hash_1:3, hash_2:1) stored at slot index 0x31
>> >> >Add record R3(hash_1:4, hash_2:3) stored at slot index 0x43
>> >> >Add record R4(hash_1:5, hash_2:4) stored at slot index 0x54
>> >> >Remove record R2
>> >> >Remove record R3
>> >> >
>> >> >---
>> >> >This was the state at step 4 of your first email, after everything
was
>> >> >added and before anything is removed:
>> >> >
>> >> >hash[1] -> 0x12(R1) -> 0x31(R2) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >hash[2] -> 0x12(R1) -> 0x31(R2) -> 0x43(R3) -> 0x54(R4)
-> MC_INVALID_VAL
>> >> >hash[3] -> 0x31(R2) -> 0x43(R3) -> 0x54(R4) ->
MC_INVALID_VAL
>> >> >hash[4] -> 0x43(R3) -> 0x54(R4) -> MC_INVALID_VAL
>> >> >hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >
>> >> >---
>> >> >So let's remove R2.
>> >> >
>> >> >This is the state (as reported by you) after R2 is removed from all
its
>> >> >chains:
>> >> >
>> >> >hash[1] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4) ->
MC_INVALID_VAL
>> >> >hash[2] -> 0x12(R1) -> 0x43(R3) -> 0x54(R4) ->
MC_INVALID_VAL
>> >> >hash[3] -> 0x43(R3) -> 0x54(R4) -> MC_INVALID_VAL
>> >> >hash[4] -> 0x43(R3) -> 0x54(R4) -> MC_INVALID_VAL
>> >> >hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >
>> >> >R2 was in chain 3 and 1, so *now* let's re-validate the
chains.
>> >> >
>> >> >First we do [3]
>> >> >- First entry is R3 (4, 3), 3 matches so we keep it.
>> >> > And now the chains to match are [3, 4] ([3] + (4, 3))
>> >> >- Second is R4 (5, 4), 4 matches so we keep it.
>> >> > And now the chains to match are [3, 4, 5] ([3, 4] + (5, 4))
>> >> >- We are done, no more elements on hash[3]
>> >> >
>> >> >Then we do hash[1]
>> >> >- First entry is R1 (1, 2), 1 matches so we keep it.
>> >> > And now the chains to match are [1, 2] ([1] + (1, 2))
>> >> >- Second entry is R3 (4, 3), it does *NOT* match any, so
>> >> > we skip it, which means pointing R1 to the next one (R4)
>> >> > Two chains are affected this way [1] and [2]:
>> >> > hash[1] -> 0x12(R1) -> 0x54(R4) -> MC_INVALID_VAL
>> >> > hash[2] -> 0x12(R1) -> 0x54(R4) -> MC_INVALID_VAL
>> >> >- Third now is R4 (5, 4) and the matching table is still [1, 2]
>> >> > It does *NOT* match once again, so we skip this too.
>> >> > R1 is now pointing at MC_INVALID_VAL which is the next value for
R4
>> >> > Two chains are affected this way [1] and [2]:
>> >> > hash[1] -> 0x12(R1) -> MC_INVALID_VAL
>> >> > hash[2] -> 0x12(R1) -> MC_INVALID_VAL
>> >> >- We are done, no more elements on hash[1]
>> >> >
>> >> >So the final status for step 5 (removal of R2) now is:
>> >> >hash[1] -> 0x12(R1) -> MC_INVALID_VAL
>> >> >hash[2] -> 0x12(R1) -> MC_INVALID_VAL
>> >> >hash[3] -> 0x43(R3) -> 0x54(R4) -> MC_INVALID_VAL
>> >> >hash[4] -> 0x43(R3) -> 0x54(R4) -> MC_INVALID_VAL
>> >> >hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >
>> >> >Now we remove R3 (4, 3), which is a quite simple operation:
>> >> >
>> >> >hash[1] -> 0x12(R1) -> MC_INVALID_VAL
>> >> >hash[2] -> 0x12(R1) -> MC_INVALID_VAL
>> >> >hash[3] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >hash[4] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >
>> >> >We have to do revalidation for chains [4], [3]
>> >> >
>> >> >First we do hash[4]
>> >> >- First entry is R4 (5, 4), 4 matches so we keep it.
>> >> > And now the chains to match are [4, 5] ([4] + (5, 4))
>> >> >- We are done, no more elements on hash[4]
>> >> >
>> >> >Then we do hash[3]
>> >> >- First entry is R4 (5, 4), it does *NOT* match any, so
>> >> > we skip it, which means pointing the head to MC_INVALID_VAL
>> >> > hash[3] -> MC_INVALID_VAL
>> >> >- We are done, no more elements on hash[3]
>> >> >
>> >> >Final status after step 6 is:
>> >> >hash[1] -> 0x12(R1) -> MC_INVALID_VAL
>> >> >hash[2] -> 0x12(R1) -> MC_INVALID_VAL
>> >> >hash[3] -> MC_INVALID_VAL
>> >> >hash[4] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >hash[5] -> 0x54(R4) -> MC_INVALID_VAL
>> >> >
>> >> >Which is the correct status.
>> >> In this case, It is correct status, but I have a counterexample.
>> >> >So re-validation of chains solves the problem as I had originally
>> >> >proposed a few patches ago :)
>> >> >
>> >>
>> >> We have records: R2(2,3) R3(4,3) R4(4,5) R5(5,6) R6(6,7)
>> >>
>> >> Steps: add R4, add R3, add R5, add R2, add R6, rm R3
>> >>
>> >>
>> >> state after addind recors: add R4, add R3, add R5, add R2, add R6
>> >>
>> >> h_table | chain
>> >> 2 -> R2 -> R6
>> >> 3 -> R3 -> R5 -> R2 -> R6
>> >> 4 -> R4 -> R3 -> R5 -> R2 -> R6
>> >> 5 -> R4 -> R3 -> R5 -> R2 -> R6
>> >> 6 -> R5 -> R2 -> R6
>> >> 7 -> R6
>> >>
>> >> Remove record R3(3,4)
>> >> a) remove R3 from chain h_table[4]
>> >> b) remove R3 from chain h_table[3]
>> >>
>> >> h_table | chain
>> >> 2 -> R2 -> R6
>> >> 3 -> R5 -> R2 -> R6
>> >> 4 -> R4 -> R5 -> R2 -> R6
>> >> 5 -> R4 -> R3 -> R5 -> R2 -> R6
>> >> 6 -> R5 -> R2 -> R6
>> >> 7 -> R6
>> >
>> >This is wrong, removing R3, removes it from chain 5 too (it was and
>> >remains identical to chain 4).
>> >
>> >> c)Revalidate chain h_table[4]
>> >>
>> >> - First entry is R4 (4, 5), 4 matches so we keep it.
>> >> And now the chains to match are [4, 5] ([4] + (4, 5))
>> >> - Second is R5 (5, 6), 5 matches so we keep it.
>> >> And now the chains to match are [4, 5, 6] ([4, 5] + (5, 6))
>> >> - Third is R2 (2, 3), no match in [4, 5, 6]
>> >> so we skip this.
>> >> R5 is now pointing at R6 which is the next value for R2
>> >>
>> >> Current state:
>> >>
>> >> h_table | chain
>> >> 2 -> R2 -> R6
>> >> 3 -> R5 -> R6
>> >> 4 -> R4 -> R5 -> R6
>> >> 5 -> R4 -> R3 -> R5 -> R6
>> >> 6 -> R5 -> R6
>> >> 7 -> R6
>> >>
>> >> R2(2, 3) should be reachable with hash key 3, bu it isn't
>> >> It is wrong.
>> >
>> >True, when thinking about re-validation I was wondering if we need to
>> >validate both chains before allowing removal of any entry.
>> >I guess we need to.
>> >
>> >So what we can do is to simply keep track of all record we would remove
>> >from the first chain we validate, then parse the second and if any pair
>> >is 'revalidated' we mark it as to not be deleted in the first
chanin
>> >either. If at the end of revalidation we have left anything to remove we
>> >do.
>> >
>> >The first entry in the chain can always be removed, so we only keep
>> >middle entries.
>> >
>> >so we keep the list of links we want to sever and what we want to keep,
>> >from the first chain, and if any is revalidated by the second one we
>> >scan we skip it.
>> >
>> >
>> >Situation after removal of R3 and before revalidation:
>> >
>> >R2(2,3) R3(4,3) R4(4,5) R5(5,6) R6(6,7)
>> >
>> >h_table | chain
>> > 2 -> R2 -> R6
>> > 3 -> R5 -> R2 -> R6
>> > 4 -> R4 -> R5 -> R2 -> R6
>> > 5 -> R4 -> R5 -> R2 -> R6
>> > 6 -> R5 -> R2 -> R6
>> > 7 -> R6
>> >
>> >During revalidation of chain 4 we have (R5, R2) as one of the links to
>> >remove after the first chain pass (chain 4), but we do not remove it
>> >yet.
>> >We also have marked as keep (R4, R5), (R5, R6) (note that I skipped R2
>> >here between R5 and R6)
>> >
>> >Then we revalidate chain 3:
>> >
>> >- first entry is R5(5,6), it doesn't match so we remove it.
>> >- then we check R2(2, 3) which matches, it is now the first of the list
>> >so we do not need to keep track of it.
>> >Check is now for [2, 3] = [3 + (2, 3)]
>> >- now we check R6, it doesn't match so we mark it for removal (R2, R6)
>> >- done
>> >
>> >Interim situation where we removed only heads of lists:
>> >h_table | chain
>> > 2 -> R2 -> R6
>> > 3 -> R2 -> R6
>> > 4 -> R4 -> R5 -> R2 -> R6
>> > 5 -> R4 -> R5 -> R2 -> R6
>> > 6 -> R5 -> R2 -> R6
>> > 7 -> R6
>> >
>> >
>> >ok now we have the following 2 lists:
>> >
>> >1. to keep: (R4, R5), (R5, R6)
>> >2. to remove: (R5, R2) (R2, R6)
>> >
>> >What we need to do here is check if any of those to remove is in the
>> >list to keep, if it is strike it out from the remove list.
>> >
>> >We start with (R5, R2) in the removal-list and check it against the
>> >keep-list.
>> >It doesn't match, so we go on and link R5->(R2->next)
>> >
>> >h_table | chain
>> > 2 -> R2 -> R6
>> > 3 -> R2 -> R6
>> > 4 -> R4 -> R5 -> R6
>> > 5 -> R4 -> R5 -> R6
>> > 6 -> R5 -> R6
>> > 7 -> R6
>> >
>> >Then we go to the second element (R2, R6), we scan the keep list and we
>> >do not find it either, so we proceed to change R2 -> (R6->next):
>> >
>> >h_table | chain
>> > 2 -> R2
>> > 3 -> R2
>> > 4 -> R4 -> R5 -> R6
>> > 5 -> R4 -> R5 -> R6
>> > 6 -> R5 -> R6
>> > 7 -> R6
>> >
>> >And we are done, we have no more removal to process and the chains look sane
and well trimmed down.
>> >
>> >Simo.
>> >
>>
>> We have records: R0(0,1); R1(1,2); R2(2,3); R3(3,4); R4(4,5); R5(5,6); R6(6,7)
>> R7(7,8);
>>
>> Steps: +R4, +R3, +R5, +R2, +R6, +R1, +R0, +R7,
>> -R1
>>
>> state after addind recors: +R4, +R3, +R5, +R2, +R6, +R1, +R0, +R7,
>>
>> h_table | chain
>> 0 -> R0 -> R7
>> 1 -> R1 -> R0 -> R7
>> 2 -> R2 -> R6 -> R1 -> R0 -> R7
>> 3 -> R3 -> R5 -> R2 -> R6 -> R1 -> R0 -> R7
>> 4 -> R4 -> R3 -> R5 -> R2 -> R6 -> R1 -> R0 -> R7
>> 5 -> R4 -> R3 -> R5 -> R2 -> R6 -> R1 -> R0 -> R7
>> 6 -> R5 -> R2 -> R6 -> R1 -> R0 -> R7
>> 7 -> R6 -> R1 -> R0 -> R7
>> 8 -> R7
>>
>> As you can see, last added record R7 is part of each
>> chain. Actually, it is only one chain and few sub-chains.
>>
>>
>> Remove R1 (it will be devided in few steps
>>
>> -- remove R1 from chains h_table[1] and h_table[2]
>> h_table | chain
>> 0 -> R0 -> R7
>> 1 -> R0 -> R7
>> 2 -> R2 -> R6 -> R0 -> R7
>> 3 -> R3 -> R5 -> R2 -> R6 -> R0 -> R7
>> 4 -> R4 -> R3 -> R5 -> R2 -> R6 -> R0 -> R7
>> 5 -> R4 -> R3 -> R5 -> R2 -> R6 -> R0 -> R7
>> 6 -> R5 -> R2 -> R6 -> R0 -> R7
>> 7 -> R6 -> R0 -> R7
>> 8 -> R7
>>
>> -- there isn't problem with the first entry in chains
>>
>> -- marking records for removing in chain h_table[1]
>> Keep :
>> Remove: (R0, R7)
>>
>> -- marking records for removing in chain h_table[2]
>> Keep :
>> Remove: (R0, R7); (R2, R6); (R6, R0);
>>
>> -- removing records from chain h_table[1]
>> What we need to do here is check if any of those to remove is in the
>> list to keep, if it is strike it out from the remove list.
>>
>> We start with (R0, R7) in the removal-list and check it against the
>> keep-list.
>> It doesn't match, so we go on and link R0->(R7->next)
>> R0-> MC_INVALID_VAL
>>
>> Current state:
>>
>> h_table | chain
>> 0 -> R0
>> 1 -> R0
>> 2 -> R2 -> R6 -> R0
>> 3 -> R3 -> R5 -> R2 -> R6 -> R0
>> 4 -> R4 -> R3 -> R5 -> R2 -> R6 -> R0
>> 5 -> R4 -> R3 -> R5 -> R2 -> R6 -> R0
>> 6 -> R5 -> R2 -> R6 -> R0
>> 7 -> R6 -> R0
>> 8 -> R7
>>
>> In this state, record R7 is *not* reachable with hash key "7"
>>
>> Revalidation of chain is very dangerous. The main problem is with single chain
>> (link-list) for different hash keys and situation is much more complicated
>> with higher collision of hash keys. This is a reason why I proposed to have
>> two next pointers in record (rec->next1, rec->next2)
>
>You got the computations wrong, however I found a different way in which
>the revalidation fails :-(
I draw examples on paper with pencil.
So, I could do a mistake when I rewrote example into mail.
>
>I was trying to keep one chain list as is to avoid changing the on disk
>format, but at this point I agree it's getting complicated beyond what
>is reasonable. If you propose a patch that adds 2 next elements I will
>review it.
>
>Simo.
>
At the moment, structure sss_mc_rec looks like
struct sss_mc_rec {
uint32_t b1; /* barrier 1 */
uint32_t len; /* total record length including record data */
uint64_t expire; /* record expiration time (cast to time_t) */
rel_ptr_t next; /* ptr of next record rel to data_table */
uint32_t hash1; /* val of first hash (usually name of record) */
uint32_t hash2; /* val of second hash (usually id of record) */
uint32_t b2; /* barrier 2 - 32 bytes mark, fits a slot */
char data[0];
};
I can see two possible solution,
1) sizeof(struct sss_mc_rec) will increase
--new member will be added to this tructure
struct sss_mc_rec {
uint32_t b1;
uint32_t len;
uint64_t expire;
rel_ptr_t next1; // "next" renamed to next1
rel_ptr_t next2; // "next2" is new member of structure
uint32_t hash1;
uint32_t hash2;
uint32_t b2;
uint32_t padding; // unused
char data[0];
};
-- MC_SLOT_SIZE will be increased from 32 -> to 40
-- reason: MC_SLOT_SIZE % sizeof(void*) should be 0 on each platform
2) sizeof(struct sss_mc_rec) will not change
struct sss_mc_rec {
uint32_t b1;
uint32_t len;
uint32_t expire_offset; // type was changed from uint64_t -> uin32_t
rel_ptr_t next1; // "next" renamed to next1
rel_ptr_t next2; // "next2" is new member of structure
uint32_t hash1;
uint32_t hash2;
uint32_t b2;
char data[0];
};
--expire_offset will be time since creation of mmap_cache.
--creation time of mmap_cache(uint64_t) will be stored in
"sss_mc_header mcc_ctx"
--reason: Year 2038 problem
Which one do you prefer?
The re is no reason to maintain 'padding' if you add a new element. The
padding was added to align the structure so that when packed it would be
exactly 32 bytes long.
However I do not understand why you are changing the expire type from 64
to 32 ?
Simo.
--
Simo Sorce * Red Hat, Inc * New York