Re: [PATCH v2 1/3] nfsd: add a usermodehelper upcall for NFSv4 client ID tracking

["J. Bruce Fields" <bfields@fieldses.org>]

On Wed, Oct 03, 2012 at 08:40:29AM -0400, Jeff Layton wrote:
> Add a new client tracker upcall type that uses call_usermodehelper to
> call out to a program. This seems to be the preferred method of
> calling out to usermode these days for seldom-called upcalls. It's
> simple and doesn't require a running daemon, so it should "just work"
> as long as the binary is installed.
> 
> The client tracking exit operation is also changed to check for a
> NULL pointer before running. The UMH upcall doesn't need to do anything
> at module teardown time.
> 
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/nfsd/nfs4recover.c | 139 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 138 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> index 43295d4..481cb3e 100644
> --- a/fs/nfsd/nfs4recover.c
> +++ b/fs/nfsd/nfs4recover.c
> @@ -926,6 +926,142 @@ static struct nfsd4_client_tracking_ops nfsd4_cld_tracking_ops = {
>  	.grace_done	= nfsd4_cld_grace_done,
>  };
>  
> +/* upcall via usermodehelper */
> +static char cltrack_prog[PATH_MAX] = "/sbin/nfsdcltrack";
> +module_param_string(cltrack_prog, cltrack_prog, sizeof(cltrack_prog),
> +			S_IRUGO|S_IWUSR);
> +MODULE_PARM_DESC(cltrack_prog, "Path to the nfsdcltrack upcall program");
> +
> +static int
> +nfsd4_cltrack_upcall(char *cmd, char *arg)
> +{
> +	char *envp[] = { "HOME=/",
> +			"TERM=linux",
> +			"PATH=/sbin:/usr/sbin:/bin:/usr/bin",

Dumb question: why does the upcall program need these environment
variables?

--b.

> +			NULL
> +	};
> +	char *argv[4];
> +	int ret;
> +
> +	if (unlikely(!cltrack_prog[0])) {
> +		dprintk("%s: cltrack_prog is disabled\n", __func__);
> +		return -EACCES;
> +	}
> +
> +	dprintk("%s: cmd: %s\n", __func__, cmd);
> +	dprintk("%s: arg: %s\n", __func__, arg ? arg : "(null)");
> +
> +	argv[0] = (char *)cltrack_prog;
> +	argv[1] = cmd;
> +	argv[2] = arg;
> +	argv[3] = NULL;
> +
> +	ret = call_usermodehelper(argv[0], argv, envp, UMH_WAIT_PROC);
> +	/*
> +	 * Disable the upcall mechanism if we're getting an ENOENT
> +	 * error. The admin can re-enable it on the fly by using sysfs
> +	 * once the problem has been fixed.
> +	 */
> +	if (ret == -ENOENT || ret == -EACCES) {
> +		printk(KERN_ERR "NFSD: %s was not found or isn't executable. "
> +			"Please reset nfsd.cltrack_prog module parameter "
> +			"once problem is resolved (%d)!\n",
> +			cltrack_prog, ret);
> +		cltrack_prog[0] = '\0';
> +	}
> +	dprintk("%s: %s return value: %d\n", __func__, cltrack_prog, ret);
> +
> +	return ret;
> +}
> +
> +static char *
> +bin_to_hex_dup(const unsigned char *src, int srclen)
> +{
> +	int i;
> +	char *buf, *hex;
> +
> +	/* +1 for terminating NULL */
> +	buf = kmalloc((srclen * 2) + 1, GFP_KERNEL);
> +	if (!buf)
> +		return buf;
> +
> +	hex = buf;
> +	for (i = 0; i < srclen; i++) {
> +		sprintf(hex, "%2.2x", *src++);
> +		hex += 2;
> +	}
> +	return buf;
> +}
> +
> +static int
> +nfsd4_umh_cltrack_init(struct net __attribute__((unused)) *net)
> +{
> +	return nfsd4_cltrack_upcall("init", NULL);
> +}
> +
> +static void
> +nfsd4_umh_cltrack_create(struct nfs4_client *clp)
> +{
> +	char *hexid;
> +
> +	hexid = bin_to_hex_dup(clp->cl_name.data, clp->cl_name.len);
> +	if (!hexid) {
> +		dprintk("%s: can't allocate memory for upcall!\n", __func__);
> +		return;
> +	}
> +	nfsd4_cltrack_upcall("create", hexid);
> +	kfree(hexid);
> +}
> +
> +static void
> +nfsd4_umh_cltrack_remove(struct nfs4_client *clp)
> +{
> +	char *hexid;
> +
> +	hexid = bin_to_hex_dup(clp->cl_name.data, clp->cl_name.len);
> +	if (!hexid) {
> +		dprintk("%s: can't allocate memory for upcall!\n", __func__);
> +		return;
> +	}
> +	nfsd4_cltrack_upcall("remove", hexid);
> +	kfree(hexid);
> +}
> +
> +static int
> +nfsd4_umh_cltrack_check(struct nfs4_client *clp)
> +{
> +	int ret;
> +	char *hexid;
> +
> +	hexid = bin_to_hex_dup(clp->cl_name.data, clp->cl_name.len);
> +	if (!hexid) {
> +		dprintk("%s: can't allocate memory for upcall!\n", __func__);
> +		return -ENOMEM;
> +	}
> +	ret = nfsd4_cltrack_upcall("check", hexid);
> +	kfree(hexid);
> +	return ret;
> +}
> +
> +static void
> +nfsd4_umh_cltrack_grace_done(struct net __attribute__((unused)) *net,
> +				time_t boot_time)
> +{
> +	char timestr[22]; /* FIXME: better way to determine max size? */
> +
> +	sprintf(timestr, "%ld", boot_time);
> +	nfsd4_cltrack_upcall("gracedone", timestr);
> +}
> +
> +static struct nfsd4_client_tracking_ops nfsd4_umh_tracking_ops = {
> +	.init		= nfsd4_umh_cltrack_init,
> +	.exit		= NULL,
> +	.create		= nfsd4_umh_cltrack_create,
> +	.remove		= nfsd4_umh_cltrack_remove,
> +	.check		= nfsd4_umh_cltrack_check,
> +	.grace_done	= nfsd4_umh_cltrack_grace_done,
> +};
> +
>  int
>  nfsd4_client_tracking_init(struct net *net)
>  {
> @@ -956,7 +1092,8 @@ void
>  nfsd4_client_tracking_exit(struct net *net)
>  {
>  	if (client_tracking_ops) {
> -		client_tracking_ops->exit(net);
> +		if (client_tracking_ops->exit)
> +			client_tracking_ops->exit(net);
>  		client_tracking_ops = NULL;
>  	}
>  }
> -- 
> 1.7.11.4
>