Re: [PATCH 37/38] knfsd: Support adding transports by writing portlist file

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

On Fri, Dec 21, 2007 at 11:52:30AM -0600, Tom Tucker wrote:
> 
> On Fri, 2007-12-14 at 18:51 -0500, J. Bruce Fields wrote:
> > On Tue, Dec 11, 2007 at 05:33:16PM -0600, Tom Tucker wrote:
> > > 
> > > Update the write handler for the portlist file to allow creating new
> > > listening endpoints on a transport. The general form of the string is:
> > > 
> > > <transport_name><space><port number>
> > > 
> > > For example:
> > > 
> > > echo "tcp 2049" > /proc/fs/nfsd/portlist
> > > 
> > > This is intended to support the creation of a listening endpoint for
> > > RDMA transports without adding #ifdef code to the nfssvc.c file.
> > > 
> > > Transports can also be removed as follows:
> > > 
> > > '-'<transport_name><space><port number>
> > > 
> > > For example:
> > > 
> > > echo "-tcp 2049" > /proc/fs/nfsd/portlist
> > > 
> > > Attempting to add a listener with an invalid transport string results
> > > in EPROTONOSUPPORT and a perror string of "Protocol not supported". 
> > > 
> > > Attempting to remove an non-existent listener (.e.g. bad proto or port)
> > > results in ENOTCONN and a perror string of 
> > > "Transport endpoint is not connected"
> > > 
> > > Signed-off-by: Tom Tucker <tom@opengridcomputing.com>
> > > ---
> > > 
> > >  fs/nfsd/nfsctl.c      |   52 ++++++++++++++++++++++++++++++++++++++++++++++++-
> > >  net/sunrpc/svc_xprt.c |    1 +
> > >  2 files changed, 52 insertions(+), 1 deletions(-)
> > > 
> > > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > > index 77dc989..5b9ed0e 100644
> > > --- a/fs/nfsd/nfsctl.c
> > > +++ b/fs/nfsd/nfsctl.c
> > > @@ -540,7 +540,7 @@ static ssize_t write_ports(struct file *file, char *buf, size_t size)
> > >  		}
> > >  		return err < 0 ? err : 0;
> > >  	}
> > > -	if (buf[0] == '-') {
> > > +	if (buf[0] == '-' && isdigit(buf[1])) {
> > >  		char *toclose = kstrdup(buf+1, GFP_KERNEL);
> > >  		int len = 0;
> > >  		if (!toclose)
> > > @@ -554,6 +554,56 @@ static ssize_t write_ports(struct file *file, char *buf, size_t size)
> > >  		kfree(toclose);
> > >  		return len;
> > >  	}
> > > +	/*
> > > +	 * Add a transport listener by writing it's transport name
> > > +	 */
> > > +	if (isalpha(buf[0])) {
> > > +		int err;
> > > +		char transport[16];
> > > +		int port;
> > > +		if (sscanf(buf, "%15s %4d", transport, &port) == 2) {
> > > +			err = nfsd_create_serv();
> > > +			if (!err) {
> > > +				if (svc_find_xprt(nfsd_serv, transport,
> > > +						  AF_UNSPEC, port))
> > > +					return -EADDRINUSE;
> > 
> > Shouldn't svc_create_xprt do this check for us itself?  (And if it
> > doesn't, isn't there some minor race between two writers both checking,
> > finding nothing, and then both svc_create_xprt()ing?)
> > 
> 
> You're right. fixed.

Thanks!  But:

> 
> > > +
> > > +				err = svc_create_xprt(nfsd_serv,
> > > +						      transport, port,
> > > +						      SVC_SOCK_ANONYMOUS);
> > > +				if (err == -ENOENT)
> > > +					/* Give a reasonable perror msg for
> > > +					 * bad transport string */
> > > +					err = -EPROTONOSUPPORT;
> > > +			}
> > > +			return err < 0 ? err : 0;
> > > +		}
> > > +	}
> > > +	/*
> > > +	 * Remove a transport by writing it's transport name and port number
> > > +	 */
> > > +	if (buf[0] == '-' && isalpha(buf[1])) {
> > > +		struct svc_xprt *xprt;
> > > +		int err = -EINVAL;
> > > +		char transport[16];
> > > +		int port;
> > > +		if (sscanf(&buf[1], "%15s %4d", transport, &port) == 2) {
> > > +			if (port == 0)
> > > +				return -EINVAL;
> > > +			lock_kernel();
> > > +			if (nfsd_serv) {
> > > +				xprt = svc_find_xprt(nfsd_serv, transport,
> > > +						     AF_UNSPEC, port);
> > > +				if (xprt) {
> > > +					svc_close_xprt(xprt);
> > > +					err = 0;
> > 
> > Hm, also: I'd have thought that svc_find_xprt should be incrementing the
> > reference count on the returned xprt, if we're expecting the caller to
> > do anything with it other than check it against NULL.

... there's still a race here, isn't there?

--b.