NFS: Add sysfs support for per-container identifier

In order to identify containers to the NFS client, we add a per-net
sysfs attribute that udev can fill with the appropriate identifier.
The identifier could be a unique hostname, but in most cases it
will probably be a persisted uuid.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

4 files changed, 135 insertions, 0 deletions

diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 0acb104f7b00..6e7aeb543f6a 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -49,6 +49,7 @@
 #include "pnfs.h"
 #include "nfs.h"
 #include "netns.h"
+#include "sysfs.h"
 
 #define NFSDBG_FACILITY         NFSDBG_CLIENT
 
@@ -1072,12 +1073,15 @@ void nfs_clients_init(struct net *net)
 #endif
         spin_lock_init(&nn->nfs_client_lock);
         nn->boot_time = ktime_get_real();
+
+        nfs_netns_sysfs_setup(nn, net);
 }
 
 void nfs_clients_exit(struct net *net)
 {
         struct nfs_net *nn = net_generic(net, nfs_net_id);
 
+        nfs_netns_sysfs_destroy(nn);
         nfs_cleanup_cb_ident_idr(net);
         WARN_ON_ONCE(!list_empty(&nn->nfs_client_list));
         WARN_ON_ONCE(!list_empty(&nn->nfs_volume_list));
diff --git a/fs/nfs/netns.h b/fs/nfs/netns.h
index fc9978c58265..c8374f74dce1 100644
--- a/fs/nfs/netns.h
+++ b/fs/nfs/netns.h
@@ -15,6 +15,8 @@ struct bl_dev_msg {
         uint32_t major, minor;
 };
 
+struct nfs_netns_client;
+
 struct nfs_net {
         struct cache_detail *nfs_dns_resolve;
         struct rpc_pipe *bl_device_pipe;
@@ -29,6 +31,7 @@ struct nfs_net {
         unsigned short nfs_callback_tcpport6;
         int cb_users[NFS4_MAX_MINOR_VERSION + 1];
 #endif
+        struct nfs_netns_client *nfs_client;
         spinlock_t nfs_client_lock;
         ktime_t boot_time;
 #ifdef CONFIG_PROC_FS
diff --git a/fs/nfs/sysfs.c b/fs/nfs/sysfs.c
index 7070711ff6c5..4f3390b20239 100644
--- a/fs/nfs/sysfs.c
+++ b/fs/nfs/sysfs.c
@@ -9,7 +9,12 @@
 #include <linux/fs.h>
 #include <linux/slab.h>
 #include <linux/netdevice.h>
+#include <linux/string.h>
+#include <linux/nfs_fs.h>
+#include <linux/rcupdate.h>
 
+#include "nfs4_fs.h"
+#include "netns.h"
 #include "sysfs.h"
 
 struct kobject *nfs_client_kobj;
@@ -67,3 +72,116 @@ void nfs_sysfs_exit(void)
         kobject_put(nfs_client_kobj);
         kset_unregister(nfs_client_kset);
 }
+
+static ssize_t nfs_netns_identifier_show(struct kobject *kobj,
+                struct kobj_attribute *attr, char *buf)
+{
+        struct nfs_netns_client *c = container_of(kobj,
+                        struct nfs_netns_client,
+                        kobject);
+        return scnprintf(buf, PAGE_SIZE, "%s\n", c->identifier);
+}
+
+/* Strip trailing '\n' */
+static size_t nfs_string_strip(const char *c, size_t len)
+{
+        while (len > 0 && c[len-1] == '\n')
+                --len;
+        return len;
+}
+
+static ssize_t nfs_netns_identifier_store(struct kobject *kobj,
+                struct kobj_attribute *attr,
+                const char *buf, size_t count)
+{
+        struct nfs_netns_client *c = container_of(kobj,
+                        struct nfs_netns_client,
+                        kobject);
+        const char *old;
+        char *p;
+        size_t len;
+
+        len = nfs_string_strip(buf, min_t(size_t, count, CONTAINER_ID_MAXLEN));
+        if (!len)
+                return 0;
+        p = kmemdup_nul(buf, len, GFP_KERNEL);
+        if (!p)
+                return -ENOMEM;
+        old = xchg(&c->identifier, p);
+        if (old) {
+                synchronize_rcu();
+                kfree(old);
+        }
+        return count;
+}
+
+static void nfs_netns_client_release(struct kobject *kobj)
+{
+        struct nfs_netns_client *c = container_of(kobj,
+                        struct nfs_netns_client,
+                        kobject);
+
+        if (c->identifier)
+                kfree(c->identifier);
+        kfree(c);
+}
+
+static const void *nfs_netns_client_namespace(struct kobject *kobj)
+{
+        return container_of(kobj, struct nfs_netns_client, kobject)->net;
+}
+
+static struct kobj_attribute nfs_netns_client_id = __ATTR(identifier,
+                0644, nfs_netns_identifier_show, nfs_netns_identifier_store);
+
+static struct attribute *nfs_netns_client_attrs[] = {
+        &nfs_netns_client_id.attr,
+        NULL,
+};
+
+static struct kobj_type nfs_netns_client_type = {
+        .release = nfs_netns_client_release,
+        .default_attrs = nfs_netns_client_attrs,
+        .sysfs_ops = &kobj_sysfs_ops,
+        .namespace = nfs_netns_client_namespace,
+};
+
+static struct nfs_netns_client *nfs_netns_client_alloc(struct kobject *parent,
+                struct net *net)
+{
+        struct nfs_netns_client *p;
+
+        p = kzalloc(sizeof(*p), GFP_KERNEL);
+        if (p) {
+                p->net = net;
+                p->kobject.kset = nfs_client_kset;
+                if (kobject_init_and_add(&p->kobject, &nfs_netns_client_type,
+                                        parent, "nfs_client") == 0)
+                        return p;
+                kobject_put(&p->kobject);
+        }
+        return NULL;
+}
+
+void nfs_netns_sysfs_setup(struct nfs_net *netns, struct net *net)
+{
+        struct nfs_netns_client *clp;
+
+        clp = nfs_netns_client_alloc(nfs_client_kobj, net);
+        if (clp) {
+                netns->nfs_client = clp;
+                kobject_uevent(&clp->kobject, KOBJ_ADD);
+        }
+}
+
+void nfs_netns_sysfs_destroy(struct nfs_net *netns)
+{
+        struct nfs_netns_client *clp = netns->nfs_client;
+
+        if (clp) {
+                kobject_uevent(&clp->kobject, KOBJ_REMOVE);
+                kobject_del(&clp->kobject);
+                kobject_put(&clp->kobject);
+                netns->nfs_client = NULL;
+        }
+}
diff --git a/fs/nfs/sysfs.h b/fs/nfs/sysfs.h
index 666f8db2ba92..f1b27411dcc0 100644
--- a/fs/nfs/sysfs.h
+++ b/fs/nfs/sysfs.h
@@ -6,10 +6,20 @@
 #ifndef __NFS_SYSFS_H
 #define __NFS_SYSFS_H
 
+#define CONTAINER_ID_MAXLEN (64)
+
+struct nfs_netns_client {
+        struct kobject kobject;
+        struct net *net;
+        const char *identifier;
+};
 
 extern struct kobject *nfs_client_kobj;
 
 extern int nfs_sysfs_init(void);
 extern void nfs_sysfs_exit(void);
 
+void nfs_netns_sysfs_setup(struct nfs_net *netns, struct net *net);
+void nfs_netns_sysfs_destroy(struct nfs_net *netns);
+
 #endif