RPC 41: MDS_STATFS
~~~~~~~~~~~~~~~~~~
[[mds-statfs-rpc]]

MDS_STATFS is an RPC that queries data about the underlying file
system for a given MDT.
////
It is generated in response to an explicit call for 'statfs'
information from the VFS via the 'statfs(2)' function.
////

The MDS_STATFS request message is a so-called "empty" message in that
it only has a buffer for the 'ptlrpc_body' with the 'pb_opc' value
MDS_STATFS (41).

The reply message conveys 'statfs' data when it succeeds, and an error
code if it doesn't.

.MDS_STATFS Generic Packet Structure

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[width="50%", cols="2a"]
|====
| request
[cols="1"]
!===================
! <<struct-ptlrpc-body,ptlrpc_body>> !
!===================
| reply
[cols="2"]
!===================
! <<struct-ptlrpc-body,ptlrpc_body>> ! <<struct-obd_statfs,obd_statfs>> !
!===================
|====

'ptlrpc_body':: RPC descriptor. Only the 'pb_opc' value (MDS_STATFS =
41) is directly relevant to the MDS_STATFS request message. The rest
of the 'ptlrpc_body' fields handle generic information about the
RPC, as discussed in <<struct-ptlrpc-body>>, including generic error
conditions. In a normal reply ('pb_type' = PTL_RPC_MSG_REPLY) the
'pb_status' field is 0.  The one error that can be returned in
'pb_status' that is speficially from OST_STATFS' handling is -ENOMEM,
which occurs if there is not enough memory to allocate a temporary
buffer for the 'statfs' data.

'obd_statfs'::
File system wide statistics corresponding to 'struct statfs' as well
as Lustre-specific information. See <<struct-obd-statfs>> for a
detailed discussion.