.\" Copyright (c) 2009 Rick Macklem, University of Guelph
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.\" $FreeBSD$
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.Dd September 7, 2007
.Dt STABLERESTART 5
.Os
.Sh NAME
.Nm nfs-stablerestart
.Nd handles restart edge conditions for the
.Tn NFS
V4 server
.Sh SYNOPSIS
.Nm nfs-stablerestart
.Sh DESCRIPTION
The
.Nm
file holds information that allows the
.Tn NFS
V4 server to restart without always returning the NFSERR_NOGRACE error, as described in the
.Tn NFS V4
server specification; see
.%T "Network File System (NFS) Version 4 Protocol \\*(tNRFC\\*(sP 3530, Section 8.6.3" .
.Pp
The first record in the file, as defined by struct nfsf_rec in
/usr/include/fs/nfs/nfsrvstate.h, holds the lease duration of the
last incarnation of the server and the number of boot times that follows.
Following this are the number of previous boot times listed in the
first record.
The lease duration is used to set the Grace Period.
The boot times
are used to avoid the unlikely occurrence of a boot time being reused,
due to a TOD clock going backwards. This record and the previous boot times with this boot time added is re-written at the
end of the Grace Period.
.Pp
The rest of the file are appended records, as defined by
struct nfst_rec in /usr/include/fs/nfs/nfsrvstate.h and are used
represent one of two things. There are records which indicate that a
client successfully aquired state and records that indicate a client's state was revoked.
State revoke records indicate that state information
for a client was discarded, due to lease expiry and an otherwise
conflicting open or lock request being made by a different client.
These records can be used
to determine if clients might have done either of the
edge conditions.
.Pp
If a client might have done either edge condition or this file is
empty or corrupted, the server returns NFSERR_NOGRACE for any reclaim
request from the client.
.Pp
For correct operation of the server, it must be ensured that the file
is written to stable storage by the time a write op with IO_SYNC specified
has returned. This might require hardware level caching to be disabled for
a local disk drive that holds the file, or similar.
.Sh FILES
.Bl -tag -width /var/db/nfs-stablerestart -compact
.It Pa /var/db/nfs-stablerestart
NFS V4 stable restart file
.El
.Sh SEE ALSO
.Xr nfsv4 4
.Xr nfsd 8
.Sh BUGS
If the file is empty, the NFS V4 server has no choice but to return
NFSERR_NOGRACE for all Reclaim requests. Although correct, this is
a highly undesirable occurrence, so the file should not be lost if
at all possible. Nfsd will not create the file if it does not
exist and will simply log a failure to start, in the hopes that the
file can be recovered from a backup. To move the file, you must edit
the nfsd sources and recompile it. This was done to discourage
accidental relocation of the file.