Re: [PATCH] SUNRPC: have soft RPC tasks return -ETIMEDOUT instead of -EIO on major connect timeout

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Sat, 2008-03-29 at 08:49 -0400, Jeff Layton wrote:
> NFSv4 background mounts do not currently work correctly. While we could
> try to fix this in userspace, I think it's really a kernel problem...
> 
> When a soft RPC tasks experiences a major timeout during a connection
> attempt, it does an rpc_exit with a return code of -EIO. For NFSv4
> mounts, this makes the mount() syscall return -EIO. mount.nfs4 then
> interprets that as a "permanent" error, and won't attempt a background
> mount when bg is specified. Fix this by making call_timeout() do the
> rpc_exit() with an error of -ETIMEDOUT.
> 
> This fixes the background mount issue, but does make other syscalls
> on soft mounts return ETIMEDOUT instead of EIO in this situation.
> 
> Comments welcome.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  net/sunrpc/clnt.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> index 8c6a7f1..b6d409e 100644
> --- a/net/sunrpc/clnt.c
> +++ b/net/sunrpc/clnt.c
> @@ -1162,7 +1162,7 @@ call_timeout(struct rpc_task *task)
>  	if (RPC_IS_SOFT(task)) {
>  		printk(KERN_NOTICE "%s: server %s not responding, timed out\n",
>  				clnt->cl_protname, clnt->cl_server);
> -		rpc_exit(task, -EIO);
> +		rpc_exit(task, -ETIMEDOUT);
>  		return;
>  	}

While that may be acceptable for the mount() syscall, I don't think
POSIX applications are quite ready to deal with ETIMEDOUT as an error
for stat() or chdir().

Userland has the clnt_geterr() function that returns more detailed 'RPC
level' errors. While that 'error function call' approach doesn't work in
a multi-threaded environment, we might still be able to add the
equivalent of a pointer to an 'rpc_err' structure to the rpc_task, and
then have functions like call_timeout() (and especially call_verify()!)
fill in more detailed error info if that pointer is non-zero?

Cheers
  Trond