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, 58 insertions, 111 deletions

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index e83103e8a6fb..a0e08d3a108c 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -9,7 +9,6 @@
  * 2 of the License, or (at your option) any later version.
  */
 
-#include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/key.h>
 #include <linux/ctype.h>
@@ -152,68 +151,33 @@ static struct afs_cell *afs_alloc_cell(struct afs_net *net,
 	init_rwsem(&cell->vl_sem);
 	INIT_LIST_HEAD(&cell->vl_list);
 	spin_lock_init(&cell->vl_lock);
-	seqlock_init(&cell->vl_addrs_lock);
-	cell->flags = (1 << AFS_CELL_FL_NOT_READY);
-
-	for (i = 0; i < AFS_CELL_MAX_ADDRS; i++) {
-		struct sockaddr_rxrpc *srx = &cell->vl_addrs[i];
-		srx->srx_family			= AF_RXRPC;
-		srx->srx_service		= VL_SERVICE;
-		srx->transport_type		= SOCK_DGRAM;
-		srx->transport.sin6.sin6_family	= AF_INET6;
-		srx->transport.sin6.sin6_port	= htons(AFS_VL_PORT);
-	}
+	cell->flags = ((1 << AFS_CELL_FL_NOT_READY) |
+		       (1 << AFS_CELL_FL_NO_LOOKUP_YET));
+	rwlock_init(&cell->vl_addrs_lock);
 
 	/* Fill in the VL server list if we were given a list of addresses to
 	 * use.
 	 */
 	if (vllist) {
-		char delim = ':';
-
-		if (strchr(vllist, ',') || !strchr(vllist, '.'))
-			delim = ',';
-
-		do {
-			struct sockaddr_rxrpc *srx = &cell->vl_addrs[cell->vl_naddrs];
-
-			if (in4_pton(vllist, -1,
-				     (u8 *)&srx->transport.sin6.sin6_addr.s6_addr32[3],
-				     delim, &vllist)) {
-				srx->transport_len = sizeof(struct sockaddr_in6);
-				srx->transport.sin6.sin6_addr.s6_addr32[0] = 0;
-				srx->transport.sin6.sin6_addr.s6_addr32[1] = 0;
-				srx->transport.sin6.sin6_addr.s6_addr32[2] = htonl(0xffff);
-			} else if (in6_pton(vllist, -1,
-					    srx->transport.sin6.sin6_addr.s6_addr,
-					    delim, &vllist)) {
-				srx->transport_len = sizeof(struct sockaddr_in6);
-				srx->transport.sin6.sin6_family	= AF_INET6;
-			} else {
-				goto bad_address;
-			}
+		struct afs_addr_list *alist;
 
-			cell->vl_naddrs++;
-			if (!*vllist)
-				break;
-			vllist++;
-
-		} while (cell->vl_naddrs < AFS_CELL_MAX_ADDRS && vllist);
+		alist = afs_parse_text_addrs(vllist, strlen(vllist), ':',
+					     VL_SERVICE, AFS_VL_PORT);
+		if (IS_ERR(alist)) {
+			ret = PTR_ERR(alist);
+			goto parse_failed;
+		}
 
-		/* Disable DNS refresh for manually-specified cells */
+		rcu_assign_pointer(cell->vl_addrs, alist);
 		cell->dns_expiry = TIME64_MAX;
-	} else {
-		/* We're going to need to 'refresh' this cell's VL server list
-		 * from the DNS before we can use it.
-		 */
-		cell->dns_expiry = S64_MIN;
 	}
 
 	_leave(" = %p", cell);
 	return cell;
 
-bad_address:
-	printk(KERN_ERR "kAFS: bad VL server IP address\n");
-	ret = -EINVAL;
+parse_failed:
+	if (ret == -EINVAL)
+		printk(KERN_ERR "kAFS: bad VL server IP address\n");
 	kfree(cell);
 	_leave(" = %d", ret);
 	return ERR_PTR(ret);
@@ -325,7 +289,6 @@ cell_already_exists:
 	if (excl) {
 		ret = -EEXIST;
 	} else {
-		ASSERTCMP(atomic_read(&cursor->usage), >=, 1);
 		afs_get_cell(cursor);
 		ret = 0;
 	}
@@ -333,8 +296,10 @@ cell_already_exists:
 	kfree(candidate);
 	if (ret == 0)
 		goto wait_for_cell;
+	goto error_noput;
 error:
 	afs_put_cell(net, cell);
+error_noput:
 	_leave(" = %d [error]", ret);
 	return ERR_PTR(ret);
 }
@@ -396,78 +361,50 @@ int afs_cell_init(struct afs_net *net, const char *rootcell)
  */
 static void afs_update_cell(struct afs_cell *cell)
 {
+	struct afs_addr_list *alist, *old;
 	time64_t now, expiry;
-	char *vllist = NULL;
-	int ret;
 
 	_enter("%s", cell->name);
 
-	ret = dns_query("afsdb", cell->name, cell->name_len,
-			"ipv4", &vllist, &expiry);
-	_debug("query %d", ret);
-	switch (ret) {
-	case 0 ... INT_MAX:
-		clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
-		clear_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
-		goto parse_dns_data;
+	alist = afs_dns_query(cell, &expiry);
+	if (IS_ERR(alist)) {
+		switch (PTR_ERR(alist)) {
+		case -ENODATA:
+			/* The DNS said that the cell does not exist */
+			set_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
+			clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
+			cell->dns_expiry = ktime_get_real_seconds() + 61;
+			break;
 
-	case -ENODATA:
-		clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
-		set_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
-		cell->dns_expiry = ktime_get_real_seconds() + 61;
-		cell->error = -EDESTADDRREQ;
-		goto out;
+		case -EAGAIN:
+		case -ECONNREFUSED:
+		default:
+			set_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
+			cell->dns_expiry = ktime_get_real_seconds() + 10;
+			break;
+		}
 
-	case -EAGAIN:
-	case -ECONNREFUSED:
-	default:
-		/* Unable to query DNS. */
-		set_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
-		cell->dns_expiry = ktime_get_real_seconds() + 10;
 		cell->error = -EDESTADDRREQ;
-		goto out;
-	}
-
-parse_dns_data:
-	write_seqlock(&cell->vl_addrs_lock);
-
-	ret = -EINVAL;
-	do {
-		struct sockaddr_rxrpc *srx = &cell->vl_addrs[cell->vl_naddrs];
-
-		if (in4_pton(vllist, -1,
-			     (u8 *)&srx->transport.sin6.sin6_addr.s6_addr32[3],
-			     ',', (const char **)&vllist)) {
-			srx->transport_len = sizeof(struct sockaddr_in6);
-			srx->transport.sin6.sin6_addr.s6_addr32[0] = 0;
-			srx->transport.sin6.sin6_addr.s6_addr32[1] = 0;
-			srx->transport.sin6.sin6_addr.s6_addr32[2] = htonl(0xffff);
-		} else if (in6_pton(vllist, -1,
-				    srx->transport.sin6.sin6_addr.s6_addr,
-				    ',', (const char **)&vllist)) {
-			srx->transport_len = sizeof(struct sockaddr_in6);
-			srx->transport.sin6.sin6_family	= AF_INET6;
-		} else {
-			goto bad_address;
-		}
+	} else {
+		clear_bit(AFS_CELL_FL_DNS_FAIL, &cell->flags);
+		clear_bit(AFS_CELL_FL_NOT_FOUND, &cell->flags);
 
-		cell->vl_naddrs++;
-		if (!*vllist)
-			break;
-		vllist++;
+		/* Exclusion on changing vl_addrs is achieved by a
+		 * non-reentrant work item.
+		 */
+		old = rcu_dereference_protected(cell->vl_addrs, true);
+		rcu_assign_pointer(cell->vl_addrs, alist);
+		cell->dns_expiry = expiry;
 
-	} while (cell->vl_naddrs < AFS_CELL_MAX_ADDRS);
+		if (old)
+			afs_put_addrlist(old);
+	}
 
-	if (cell->vl_naddrs < AFS_CELL_MAX_ADDRS)
-		memset(cell->vl_addrs + cell->vl_naddrs, 0,
-		       (AFS_CELL_MAX_ADDRS - cell->vl_naddrs) * sizeof(cell->vl_addrs[0]));
+	if (test_and_clear_bit(AFS_CELL_FL_NO_LOOKUP_YET, &cell->flags))
+		wake_up_bit(&cell->flags, AFS_CELL_FL_NO_LOOKUP_YET);
 
 	now = ktime_get_real_seconds();
-	cell->dns_expiry = expiry;
-	afs_set_cell_timer(cell->net, expiry - now);
-bad_address:
-	write_sequnlock(&cell->vl_addrs_lock);
-out:
+	afs_set_cell_timer(cell->net, cell->dns_expiry - now);
 	_leave("");
 }
 
@@ -482,6 +419,7 @@ static void afs_cell_destroy(struct rcu_head *rcu)
 
 	ASSERTCMP(atomic_read(&cell->usage), ==, 0);
 
+	afs_put_addrlist(cell->vl_addrs);
 	key_put(cell->anonymous_key);
 	kfree(cell);
 
@@ -515,6 +453,15 @@ void afs_cells_timer(struct timer_list *timer)
 }
 
 /*
+ * Get a reference on a cell record.
+ */
+struct afs_cell *afs_get_cell(struct afs_cell *cell)
+{
+	atomic_inc(&cell->usage);
+	return cell;
+}
+
+/*
  * Drop a reference on a cell record.
  */
 void afs_put_cell(struct afs_net *net, struct afs_cell *cell)