NFS: Add a mount option to make ENETUNREACH errors fatal

If the NFS client was initially created in a container, and that
container is torn down, there is usually no possibity to go back and
destroy any NFS clients that are hung because their virtual network
devices have been unlinked.

Add a flag that tells the NFS client that in these circumstances, it
should treat ENETDOWN and ENETUNREACH errors as fatal to the NFS client.

The option defaults to being on when the mount happens from inside a net
namespace that is not "init_net".

Signed-off-by: Trond Myklebust <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Tested-by: Jeff Layton <[e-mail]>
Acked-by: Chuck Lever <[e-mail]>

fs/nfs/fs_context.c

···
 	Opt_clientaddr,
 	Opt_cto,
 	Opt_alignwrite,
+	Opt_fatal_neterrors,
 	Opt_fg,
 	Opt_fscache,
 	Opt_fscache_flag,
···
 	Opt_wsize,
 	Opt_write,
 	Opt_xprtsec,
+};
+
+enum {
+	Opt_fatal_neterrors_default,
+	Opt_fatal_neterrors_enetunreach,
+	Opt_fatal_neterrors_none,
+};
+
+static const struct constant_table nfs_param_enums_fatal_neterrors[] = {
+	{ "default",			Opt_fatal_neterrors_default },
+	{ "ENETDOWN:ENETUNREACH",	Opt_fatal_neterrors_enetunreach },
+	{ "ENETUNREACH:ENETDOWN",	Opt_fatal_neterrors_enetunreach },
+	{ "none",			Opt_fatal_neterrors_none },
+	{}
 };
 
 enum {
···
 	fsparam_string("clientaddr",	Opt_clientaddr),
 	fsparam_flag_no("cto",		Opt_cto),
 	fsparam_flag_no("alignwrite",	Opt_alignwrite),
+	fsparam_enum("fatal_neterrors", Opt_fatal_neterrors,
+		     nfs_param_enums_fatal_neterrors),
 	fsparam_flag  ("fg",		Opt_fg),
 	fsparam_flag_no("fsc",		Opt_fscache_flag),
 	fsparam_string("fsc",		Opt_fscache),
···
 		if (result.uint_32 < 1 || result.uint_32 > NFS_MAX_TRANSPORTS)
 			goto out_of_bounds;
 		ctx->nfs_server.max_connect = result.uint_32;
+		break;
+	case Opt_fatal_neterrors:
+		trace_nfs_mount_assign(param->key, param->string);
+		switch (result.uint_32) {
+		case Opt_fatal_neterrors_default:
+			if (fc->net_ns != &init_net)
+				ctx->flags |= NFS_MOUNT_NETUNREACH_FATAL;
+			else
+				ctx->flags &= ~NFS_MOUNT_NETUNREACH_FATAL;
+			break;
+		case Opt_fatal_neterrors_enetunreach:
+			ctx->flags |= NFS_MOUNT_NETUNREACH_FATAL;
+			break;
+		case Opt_fatal_neterrors_none:
+			ctx->flags &= ~NFS_MOUNT_NETUNREACH_FATAL;
+			break;
+		default:
+			goto out_invalid_value;
+		}
 		break;
 	case Opt_lookupcache:
 		trace_nfs_mount_assign(param->key, param->string);
···
 		ctx->xprtsec.policy	= RPC_XPRTSEC_NONE;
 		ctx->xprtsec.cert_serial	= TLS_NO_CERT;
 		ctx->xprtsec.privkey_serial	= TLS_NO_PRIVKEY;
+
+		if (fc->net_ns != &init_net)
+			ctx->flags |= NFS_MOUNT_NETUNREACH_FATAL;
 
 		fc->s_iflags		|= SB_I_STABLE_WRITES;
 	}

fs/nfs/super.c

···
 		{ NFS_MOUNT_FORCE_RDIRPLUS, ",rdirplus=force", "" },
 		{ NFS_MOUNT_UNSHARED, ",nosharecache", "" },
 		{ NFS_MOUNT_NORESVPORT, ",noresvport", "" },
+		{ NFS_MOUNT_NETUNREACH_FATAL,
+		  ",fatal_neterrors=ENETDOWN:ENETUNREACH",
+		  ",fatal_neterrors=none" },
 		{ 0, NULL, NULL }
 	};
 	const struct proc_nfs_info *nfs_infop;

include/linux/nfs_fs_sb.h

···
 #define NFS_MOUNT_SHUTDOWN			0x08000000
 #define NFS_MOUNT_NO_ALIGNWRITE		0x10000000
 #define NFS_MOUNT_FORCE_RDIRPLUS	0x20000000
+#define NFS_MOUNT_NETUNREACH_FATAL	0x40000000
 
 	unsigned int		fattr_valid;	/* Valid attributes */
 	unsigned int		caps;		/* server capabilities */