On Mon, 25 Mar 2013, Alex Elder wrote:
> On 03/19/2013 05:48 PM, Sage Weil wrote:
> > This is an old protocol extension that allows the client and server to
> > avoid resending old messages after a reconnect (following a socket error).
> > Instead, the exchange their sequence numbers during the handshake. This
> > avoids sending a bunch of useless data over the socket.
> >
> > It has been supported in the server code since v0.22 (Sep 2010).
>
> OK, a few comments below, but this looks good to me.
> Make the suggested (or implied) changes below if you
> like, but either way:
>
> Reviewed-by: Alex Elder <[email protected]>
>
> > Signed-off-by: Sage Weil <[email protected]>
> > ---
> > include/linux/ceph/ceph_features.h | 2 ++
> > include/linux/ceph/msgr.h | 1 +
> > net/ceph/messenger.c | 47
> > +++++++++++++++++++++++++++++++++---
> > 3 files changed, 46 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/ceph/ceph_features.h
> > b/include/linux/ceph/ceph_features.h
> > index 76554ce..4c420803 100644
> > --- a/include/linux/ceph/ceph_features.h
> > +++ b/include/linux/ceph/ceph_features.h
> > @@ -41,6 +41,7 @@
> > */
> > #define CEPH_FEATURES_SUPPORTED_DEFAULT \
> > (CEPH_FEATURE_NOSRCADDR | \
> > + CEPH_FEATURE_RECONNECT_SEQ | \
> > CEPH_FEATURE_PGID64 | \
> > CEPH_FEATURE_PGPOOL3 | \
> > CEPH_FEATURE_OSDENC | \
> > @@ -51,6 +52,7 @@
> >
> > #define CEPH_FEATURES_REQUIRED_DEFAULT \
> > (CEPH_FEATURE_NOSRCADDR | \
> > + CEPH_FEATURE_RECONNECT_SEQ | \
> > CEPH_FEATURE_PGID64 | \
> > CEPH_FEATURE_PGPOOL3 | \
> > CEPH_FEATURE_OSDENC)
>
> Is it really a required feature?
I suppose not, but it's been present since v0.32 or something crazy-old,
so there's not much point in considering the not-supported version. The
only way to really test it would be to misreport whether the client
supports it, so I'm not sure it's worth the effort.
> If the other end doesn't support it is there any
> reason we can't fall back to the old behavior?
>
> This code is only *responding* to a SEQ tag, it doesn't
> initiate one. If one is never sent by the server the
> behavior remains correct, just slower.
>
> I also have two points you might help clarify for me:
> - Is this a server initiated feature, or could a client
> send it?
The server initiates.
> - Because it's a tagged bit of message data it really
> could occur at any time--though at the end of a
> reconnect negotiation is where it's valuable. Correct?
True, although the server never does that.
I'll combine those blocks below and then push. Thanks!
sage
>
> > diff --git a/include/linux/ceph/msgr.h b/include/linux/ceph/msgr.h
> > index 680d3d6..3d94a73 100644
> > --- a/include/linux/ceph/msgr.h
> > +++ b/include/linux/ceph/msgr.h
> > @@ -87,6 +87,7 @@ struct ceph_entity_inst {
> > #define CEPH_MSGR_TAG_BADPROTOVER 10 /* bad protocol version */
> > #define CEPH_MSGR_TAG_BADAUTHORIZER 11 /* bad authorizer */
> > #define CEPH_MSGR_TAG_FEATURES 12 /* insufficient features */
> > +#define CEPH_MSGR_TAG_SEQ 13 /* 64-bit int follows with seen seq
> > number */
> >
> >
> > /*
> > diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
> > index 997dacc..2bf2806 100644
> > --- a/net/ceph/messenger.c
> > +++ b/net/ceph/messenger.c
> > @@ -1247,6 +1247,24 @@ static void prepare_write_ack(struct ceph_connection
> > *con)
> > }
> >
> > /*
> > + * Prepare to share the seq during handshake
> > + */
> > +static void prepare_write_seq(struct ceph_connection *con)
> > +{
> > + dout("prepare_write_seq %p %llu -> %llu\n", con,
> > + con->in_seq_acked, con->in_seq);
> > + con->in_seq_acked = con->in_seq;
> > +
> > + con_out_kvec_reset(con);
> > +
> > + con->out_temp_ack = cpu_to_le64(con->in_seq_acked);
> > + con_out_kvec_add(con, sizeof (con->out_temp_ack),
> > + &con->out_temp_ack);
> > +
> > + con_flag_set(con, CON_FLAG_WRITE_PENDING);
> > +}
> > +
> > +/*
> > * Prepare to write keepalive byte.
> > */
> > static void prepare_write_keepalive(struct ceph_connection *con)
> > @@ -1582,6 +1600,13 @@ static void prepare_read_ack(struct ceph_connection
> > *con)
> > con->in_base_pos = 0;
> > }
> >
> > +static void prepare_read_seq(struct ceph_connection *con)
> > +{
> > + dout("prepare_read_seq %p\n", con);
> > + con->in_base_pos = 0;
> > + con->in_tag = CEPH_MSGR_TAG_SEQ;
> > +}
> > +
> > static void prepare_read_tag(struct ceph_connection *con)
> > {
> > dout("prepare_read_tag %p\n", con);
> > @@ -2059,6 +2084,7 @@ static int process_connect(struct ceph_connection
> > *con)
> > prepare_read_connect(con);
> > break;
> >
> > + case CEPH_MSGR_TAG_SEQ:
> > case CEPH_MSGR_TAG_READY:
> > if (req_feat & ~server_feat) {
> > pr_err("%s%lld %s protocol feature mismatch,"
> > @@ -2089,7 +2115,12 @@ static int process_connect(struct ceph_connection
> > *con)
> >
> > con->delay = 0; /* reset backoff memory */
> >
> > - prepare_read_tag(con);
> > + if (con->in_reply.tag == CEPH_MSGR_TAG_SEQ) {
> > + prepare_write_seq(con);
> > + prepare_read_seq(con);
> > + } else {
> > + prepare_read_tag(con);
> > + }
> > break;
> >
> > case CEPH_MSGR_TAG_WAIT:
> > @@ -2123,7 +2154,6 @@ static int read_partial_ack(struct ceph_connection
> > *con)
> > return read_partial(con, end, size, &con->in_temp_ack);
> > }
> >
> > -
> > /*
> > * We can finally discard anything that's been acked.
> > */
> > @@ -2148,8 +2178,6 @@ static void process_ack(struct ceph_connection *con)
> > }
> >
> >
> > -
> > -
> > static int read_partial_message_section(struct ceph_connection *con,
> > struct kvec *section,
> > unsigned int sec_len, u32 *crc)
> > @@ -2628,6 +2656,17 @@ more:
> > if (con->in_base_pos)
> > goto more;
> > }
> > + if (con->in_tag == CEPH_MSGR_TAG_SEQ) {
> > + /*
> > + * the final seq exchange is semantically equivalent
> > + * to an ACK; re-use those helpers.
> > + */
> > + ret = read_partial_ack(con);
> > + if (ret <= 0)
> > + goto out;
> > + process_ack(con);
> > + goto more;
> > + }
>
> This block (above) is identical to the block a little later on
> that handles CEPH_MSGR_TAG_ACK. It might be nice to make that
> fact obvious by combining them (and if so, I would say here, not
> below). (It's OK as-is, however.)
>
> > if (con->in_tag == CEPH_MSGR_TAG_READY) {
> > /*
> > * what's next?
> >
>
>
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