From: Fan Yong <fan.yong@xxxxxxxxx> The 'fld_read_server' uses 'RMF_GENERIC_DATA' to hold the 'FLD_QUERY' RPC reply that is composed of 'struct lu_seq_range_array'. But there is not registered swabber function for 'RMF_GENERIC_DATA'. So the RPC peers need to handle the RPC reply with fixed little-endian format. In theory, we can define new structure with some swabber registered to handle the 'FLD_QUERY' RPC reply result automatically. But from the implementation view, it is not easy to be done within current 'struct req_msg_field' framework. Because the sequence range array in the RPC reply is not fixed length, instead, its length depends on 'lu_seq_range' count, that is unknown when prepare the RPC buffer. Generally, for such flexible length RPC usage, there will be a field in the RPC layout to indicate the data length. But for the 'FLD_READ' RPC, we have no way to do that unless we add new length filed that will broken the on-wire RPC protocol and cause interoperability trouble with old peer. Signed-off-by: Fan Yong <fan.yong@xxxxxxxxx> Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-6284 Reviewed-on: http://review.whamcloud.com/22309 Reviewed-by: Andreas Dilger <andreas.dilger@xxxxxxxxx> Reviewed-by: James Simmons <uja.ornl@xxxxxxxxx> Signed-off-by: James Simmons <jsimmons@xxxxxxxxxxxxx> --- drivers/staging/lustre/lustre/ptlrpc/layout.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/drivers/staging/lustre/lustre/ptlrpc/layout.c b/drivers/staging/lustre/lustre/ptlrpc/layout.c index 99d7c66..2052848 100644 --- a/drivers/staging/lustre/lustre/ptlrpc/layout.c +++ b/drivers/staging/lustre/lustre/ptlrpc/layout.c @@ -1181,6 +1181,23 @@ struct req_format RQF_FLD_QUERY = DEFINE_REQ_FMT0("FLD_QUERY", fld_query_client, fld_query_server); EXPORT_SYMBOL(RQF_FLD_QUERY); +/* + * The 'fld_read_server' uses 'RMF_GENERIC_DATA' to hold the 'FLD_QUERY' + * RPC reply that is composed of 'struct lu_seq_range_array'. But there + * is not registered swabber function for 'RMF_GENERIC_DATA'. So the RPC + * peers need to handle the RPC reply with fixed little-endian format. + * + * In theory, we can define new structure with some swabber registered to + * handle the 'FLD_QUERY' RPC reply result automatically. But from the + * implementation view, it is not easy to be done within current "struct + * req_msg_field" framework. Because the sequence range array in the RPC + * reply is not fixed length, instead, its length depends on 'lu_seq_range' + * count, that is unknown when prepare the RPC buffer. Generally, for such + * flexible length RPC usage, there will be a field in the RPC layout to + * indicate the data length. But for the 'FLD_READ' RPC, we have no way to + * do that unless we add new length filed that will broken the on-wire RPC + * protocol and cause interoperability trouble with old peer. + */ struct req_format RQF_FLD_READ = DEFINE_REQ_FMT0("FLD_READ", fld_read_client, fld_read_server); EXPORT_SYMBOL(RQF_FLD_READ); -- 1.8.3.1 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
