Document the interaction between the mountproto= and the proto= mount options in a new subsection of nfs(5). Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> --- utils/mount/nfs.man | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 81 insertions(+), 0 deletions(-) diff --git a/utils/mount/nfs.man b/utils/mount/nfs.man index b1037a8..48f2153 100644 --- a/utils/mount/nfs.man +++ b/utils/mount/nfs.man @@ -831,6 +831,87 @@ and .B wsize can safely be allowed to default to the largest values supported by both client and server, independent of the network's MTU size. +.SS "Interaction between the proto and mountproto options" +The Linux NFS client can use a different transport protocol for +contacting an NFS server's rpcbind service, its mountd service, +its NLM service, and its NFS service. +The exact transport protocols employed by the Linux NFS client for +each mount point depends on the settings of the transport protocol +mount options, which include +.BR proto , +.BR mountproto , +.BR udp ", and " tcp . +.P +The NSM protocol uses the UDP transport +no matter what transport specific options are specified. +The NFSACL protocol shares the same RPC transport as the main NFS +service. +.P +If no transport protocol options are specified, the Linux NFS client +uses UDP to contact the server's mountd service, and TCP to +contact its NLM and NFS services by default. +.P +UDP is a good choice for contacting the mountd server since most +common NFS servers support UDP for mountd, UDP generates less network +traffic, and UDP does not leave extra ports in TIME_WAIT after the +mountd request is complete. +However, a reliable stream transport such as TCP is a good choice for +NFS and NLM because these must handle large requests and must be +immune to network problems that might cause RPC requests to be lost. +.P +If the server does not support these transports for these services, the +.BR mount (8) +command attempts to discover what the server supports, and then retries +the mount request once using the discovered transport protocols. +If the server does not advertise any transport supported by the client +or is misconfigured, the mount request fails. +If the +.B bg +option is in effect, the mount command backgrounds itself and continues +to attempt the specified mount request. +.P +When the +.B proto +option, the +.B udp +option, or the +.B tcp +option is specified but the +.B mountproto +option is not, the specified transport is used to contact +both the server's mountd service and for the NLM and NFS services. +.P +If the +.B mountproto +option is specified but none of the +.BR proto ", " udp " or " tcp +options are specified, then the specified transport is used for the +initial mountd request, but the mount command attempts to discover +what the server supports for the NFS protocol, preferring TCP if +both transports are supported. +.P +If both the +.BR mountproto " and " proto +(or +.BR udp " or " tcp ) +options are specified, then the transport specified by the +.B mountproto +option is used for the initial mountd request, and the transport +specified by the +.B proto +option (or the +.BR udp " or " tcp " options)" +is used for NFS, no matter what order these options appear. +No automatic service discovery is performed if these options are +specified. +.P +If any of the +.BR proto ", " udp ", " tcp ", " +or +.B mountproto +options are specified more than once on the same mount command line, +then the value of the rightmost instance of each of these options +takes effect. .SH "DATA AND METADATA COHERENCE" Some modern cluster file systems provide perfect cache coherence among their clients. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
