afs: Add an address list concept

Add an RCU replaceable address list structure to hold a list of server
addresses.  The list also holds the

To this end:

 (1) A cell's VL server address list can be loaded directly via insmod or
     echo to /proc/fs/afs/cells or dynamically from a DNS query for AFSDB
     or SRV records.

 (2) Anyone wanting to use a cell's VL server address must wait until the
     cell record comes online and has tried to obtain some addresses.

 (3) An FS server's address list, for the moment, has a single entry that
     is the key to the server list.  This will change in the future when a
     server is instead keyed on its UUID and the VL.GetAddrsU operation is
     used.

 (4) An 'address cursor' concept is introduced to handle iteration through
     the address list.  This is passed to the afs_make_call() as, in the
     future, stuff (such as abort code) that doesn't outlast the call will
     be returned in it.

In the future, we might want to annotate the list with information about
how each address fares.  We might then want to propagate such annotations
over address list replacement.

Whilst we're at it, we allow IPv6 addresses to be specified in
colon-delimited lists by enclosing them in square brackets.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 11 insertions, 12 deletions

diff --git a/fs/afs/proc.c b/fs/afs/proc.c
index 08565429615d..9cf9ce88a8dd 100644
--- a/fs/afs/proc.c
+++ b/fs/afs/proc.c
@@ -514,23 +514,23 @@ static int afs_proc_cell_vlservers_open(struct inode *inode, struct file *file)
  */
 static void *afs_proc_cell_vlservers_start(struct seq_file *m, loff_t *_pos)
 {
+	struct afs_addr_list *alist;
 	struct afs_cell *cell = m->private;
 	loff_t pos = *_pos;
 
-	_enter("cell=%p pos=%Ld", cell, *_pos);
+	rcu_read_lock();
 
-	/* lock the list against modification */
-	down_read(&cell->vl_sem);
+	alist = rcu_dereference(cell->vl_addrs);
 
 	/* allow for the header line */
 	if (!pos)
 		return (void *) 1;
 	pos--;
 
-	if (pos >= cell->vl_naddrs)
+	if (!alist || pos >= alist->nr_addrs)
 		return NULL;
 
-	return &cell->vl_addrs[pos];
+	return alist->addrs + pos;
 }
 
 /*
@@ -539,17 +539,18 @@ static void *afs_proc_cell_vlservers_start(struct seq_file *m, loff_t *_pos)
 static void *afs_proc_cell_vlservers_next(struct seq_file *p, void *v,
 					  loff_t *_pos)
 {
+	struct afs_addr_list *alist;
 	struct afs_cell *cell = p->private;
 	loff_t pos;
 
-	_enter("cell=%p{nad=%u} pos=%Ld", cell, cell->vl_naddrs, *_pos);
+	alist = rcu_dereference(cell->vl_addrs);
 
 	pos = *_pos;
 	(*_pos)++;
-	if (pos >= cell->vl_naddrs)
+	if (!alist || pos >= alist->nr_addrs)
 		return NULL;
 
-	return &cell->vl_addrs[pos];
+	return alist->addrs + pos;
 }
 
 /*
@@ -557,9 +558,7 @@ static void *afs_proc_cell_vlservers_next(struct seq_file *p, void *v,
  */
 static void afs_proc_cell_vlservers_stop(struct seq_file *p, void *v)
 {
-	struct afs_cell *cell = p->private;
-
-	up_read(&cell->vl_sem);
+	rcu_read_unlock();
 }
 
 /*
@@ -658,7 +657,7 @@ static int afs_proc_cell_servers_show(struct seq_file *m, void *v)
 	}
 
 	/* display one cell per line on subsequent lines */
-	sprintf(ipaddr, "%pISp", &server->addr.transport);
+	sprintf(ipaddr, "%pISp", &server->addrs->addrs[0].transport);
 	seq_printf(m, "%3d %-15s %5d\n",
 		   atomic_read(&server->usage), ipaddr, server->fs_state);