Date:   Sat, 15 Dec 2018 13:50:35 +1100
From:   Vincent McIntyre <vincent.mcintyre@csiro.au>
To:     <linux-nfs@vger.kernel.org>
Subject: mount option timeo - in deciseconds, or seconds?
Message-ID: <20181215025034.j5zyfytvxqt35woz@mayhem.atnf.CSIRO.AU>
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Hi,

I've been trying to figure out why the nfs.man manpage states

  .BI timeo= n
  The time in deciseconds (tenths of a second) the NFS client waits for a
  response before it retries an NFS request.

Can someone who actually understands NFS enlighten me?
Here's where I'm up to.

I looked in the upstream git.
The 'deciseconds' has been in there since the start of git history
(2007, commit id 16db99b56a532bf56fa27618a6ef30763cd9006f).
But is it (still) correct?

Unfortunately I can't see a direct use of the 'timeo' field
of the NFS data structure so the answer is not easily found.

In utils/mount/nfsmount.c mountnfs() we have

 timeout = time(NULL) + 60 * retry;

This sets the upper bound for how long to wait for a mount to succeed.
The units are seconds, because retry is given in minutes.

Also we see

 prevt = 0;
 t = 30;
 val = 1;

these are the control variables for the loop
The main check that prolongs the waiting time is

            if (t - prevt < 30)
                sleep(30);
             ....if not mounted yet...
            prevt = t;

The decision to time out is made like this
            t = time(NULL);
            if (t >= timeout) {
                rpc_mount_errors(*nfs_server.hostname, 0, bg);
                goto fail;
            }

so it seems clear that t should also have the units of seconds.
That also matches up with the declaration of t & timeout as time_t.

But I still don't see how data.timo gets used.
utils/mount/network.h defines this

  static const struct timeval TIMEOUT = { 20, 0 };
and
  #define MOUNT_TIMEOUT   (30)

which would seem to be in units of seconds,
since eg. connect_to() uses seconds
which reaches it via the calling path:

1.
 CLIENT *mnt_openclnt(clnt_addr_t *mnt_server, int *msock)
{
...
    *msock = get_socket(mnt_saddr, mnt_pmap->pm_prot, MOUNT_TIMEOUT,
                TRUE, FALSE);

2.
static int get_socket(struct sockaddr_in *saddr, unsigned int p_prot,
            unsigned int timeout, int resvp, int conn)
{
...
        cc = connect_to(so, SAFE_SOCKADDR(saddr), namelen,
                timeout);
3.
/*
 * Attempt to connect a socket, but time out after "timeout" seconds.
 *
 * On error return, caller closes the socket.
 */
static int connect_to(int fd, struct sockaddr *addr,
            socklen_t addrlen, int timeout)
{


Thanks
Vince