lk/linux-kernel-test
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

dccp ccid-2: Implementation of circular Ack Vector buffer with overflow handling

Browse Source 
This completes the implementation of a circular buffer for Ack Vectors, by
extending the current (linear array-based) implementation.  The changes are:

 (a) An `overflow' flag to deal with the case of overflow. As before, dynamic
     growth of the buffer will not be supported; but code will be added to deal
     robustly with overflowing Ack Vector buffers.

 (b) A `tail_seqno' field. When naively implementing the algorithm of Appendix A
     in RFC 4340, problems arise whenever subsequent Ack Vector records overlap,
     which can bring the entire run length calculation completely out of synch.
     (This is documented on http://www.erg.abdn.ac.uk/users/gerrit/dccp/notes/\
                                             ack_vectors/tracking_tail_ackno/ .)
 (c) The buffer length is now computed dynamically (i.e. current fill level),
     as the span between head to tail.

As a result, dccp_ackvec_pending() is now simpler - the #ifdef is no longer
necessary since buf_empty is always true when IP_DCCP_ACKVEC is not configured.

Signed-off-by: Gerrit Renker <gerrit@erg.abdn.ac.uk>
This commit is contained in:
Gerrit Renker
2010-11-10 21:21:35 +01:00
parent 7d87093660
commit b3d14bff12
4 changed files with 50 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
net/dccp/ackvec.c
View File

@@ -29,7 +29,7 @@ struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);
if (av != NULL) {
av->av_buf_head = DCCPAV_MAX_ACKVEC_LEN - 1;
av->av_buf_head = av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
INIT_LIST_HEAD(&av->av_records);
}
return av;
@@ -71,6 +71,14 @@ int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
avr->avr_ack_ackno = av->av_buf_ackno;
avr->avr_ack_nonce = nonce_sum;
avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
/*
* When the buffer overflows, we keep no more than one record. This is
* the simplest way of disambiguating sender-Acks dating from before the
* overflow from sender-Acks which refer to after the overflow; a simple
* solution is preferable here since we are handling an exception.
*/
if (av->av_overflow)
dccp_ackvec_purge_records(av);
/*
* Since GSS is incremented for each packet, the list is automatically
* arranged in descending order of @ack_seqno.
@@ -84,6 +92,27 @@ int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
return 0;
}
/*
* Buffer index and length computation using modulo-buffersize arithmetic.
* Note that, as pointers move from right to left, head is `before' tail.
*/
static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
{
return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
}
static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
{
return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
}
u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
{
if (unlikely(av->av_overflow))
return DCCPAV_MAX_ACKVEC_LEN;
return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
}
/*
* If several packets are missing, the HC-Receiver may prefer to enter multiple
* bytes with run length 0, rather than a single byte with a larger run length;