AFS: Implement an autocell mount capability [ver #2]

Implement the ability for the root directory of a mounted AFS filesystem to
accept lookups of arbitrary directory names, to interpet the names as the names
of cells, to look the cell names up in the DNS for AFSDB records and to mount
the root.cell volume of the nominated cell on the pseudo-directory created by
lookup.

This facility is requested by passing:

	-o autocell

to the mountpoint for which this is desired, usually the /afs mount.

To use this facility, a DNS upcall program is required for AFSDB records.  This
can be obtained from:

	http://people.redhat.com/~dhowells/afs/dns.afsdb.c

It should be compiled with -lresolv and -lkeyutils and installed as, say:

	/usr/sbin/dns.afsdb

Then the following line needs to be added to /sbin/request-key.conf:

	create	dns_resolver afsdb:*	*	/usr/sbin/dns.afsdb %k

This can be tested by mounting AFS, say:

	insmod dns_resolver.ko
	insmod af-rxrpc.ko
	insmod kafs.ko rootcell=grand.central.org
	mount -t afs "#grand.central.org:root.cell." /afs -o autocell

and doing:

	ls /afs/grand.central.org/

which should show:

	archive/  cvs/  doc/  local/  project/  service/  software/  user/  www/

if it works.

Signed-off-by: Wang Lei <wang840925@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

1 files changed, 86 insertions, 0 deletions

diff --git a/fs/afs/inode.c b/fs/afs/inode.c
index 320ffef11574..0747339011c3 100644
--- a/fs/afs/inode.c
+++ b/fs/afs/inode.c
@@ -19,6 +19,8 @@
 #include <linux/fs.h>
 #include <linux/pagemap.h>
 #include <linux/sched.h>
+#include <linux/mount.h>
+#include <linux/namei.h>
 #include "internal.h"
 
 struct afs_iget_data {
@@ -102,6 +104,16 @@ static int afs_iget5_test(struct inode *inode, void *opaque)
 }
 
 /*
+ * iget5() comparator for inode created by autocell operations
+ *
+ * These pseudo inodes don't match anything.
+ */
+static int afs_iget5_autocell_test(struct inode *inode, void *opaque)
+{
+        return 0;
+}
+
+/*
  * iget5() inode initialiser
  */
 static int afs_iget5_set(struct inode *inode, void *opaque)
@@ -118,6 +130,67 @@ static int afs_iget5_set(struct inode *inode, void *opaque)
 }
 
 /*
+ * inode retrieval for autocell
+ */
+struct inode *afs_iget_autocell(struct inode *dir, const char *dev_name,
+                                int namesz, struct key *key)
+{
+        struct afs_iget_data data;
+        struct afs_super_info *as;
+        struct afs_vnode *vnode;
+        struct super_block *sb;
+        struct inode *inode;
+        static atomic_t afs_autocell_ino;
+
+        _enter("{%x:%u},%*.*s,",
+               AFS_FS_I(dir)->fid.vid, AFS_FS_I(dir)->fid.vnode,
+               namesz, namesz, dev_name ?: "");
+
+        sb = dir->i_sb;
+        as = sb->s_fs_info;
+        data.volume = as->volume;
+        data.fid.vid = as->volume->vid;
+        data.fid.unique = 0;
+        data.fid.vnode = 0;
+
+        inode = iget5_locked(sb, atomic_inc_return(&afs_autocell_ino),
+                             afs_iget5_autocell_test, afs_iget5_set,
+                             &data);
+        if (!inode) {
+                _leave(" = -ENOMEM");
+                return ERR_PTR(-ENOMEM);
+        }
+
+        _debug("GOT INODE %p { ino=%lu, vl=%x, vn=%x, u=%x }",
+               inode, inode->i_ino, data.fid.vid, data.fid.vnode,
+               data.fid.unique);
+
+        vnode = AFS_FS_I(inode);
+
+        /* there shouldn't be an existing inode */
+        BUG_ON(!(inode->i_state & I_NEW));
+
+        inode->i_size           = 0;
+        inode->i_mode           = S_IFDIR | S_IRUGO | S_IXUGO;
+        inode->i_op             = &afs_autocell_inode_operations;
+        inode->i_nlink          = 2;
+        inode->i_uid            = 0;
+        inode->i_gid            = 0;
+        inode->i_ctime.tv_sec   = get_seconds();
+        inode->i_ctime.tv_nsec  = 0;
+        inode->i_atime          = inode->i_mtime = inode->i_ctime;
+        inode->i_blocks         = 0;
+        inode->i_version        = 0;
+        inode->i_generation     = 0;
+
+        set_bit(AFS_VNODE_PSEUDODIR, &vnode->flags);
+        inode->i_flags |= S_NOATIME;
+        unlock_new_inode(inode);
+        _leave(" = %p", inode);
+        return inode;
+}
+
+/*
  * inode retrieval
  */
 struct inode *afs_iget(struct super_block *sb, struct key *key,
@@ -314,6 +387,19 @@ int afs_getattr(struct vfsmount *mnt, struct dentry *dentry,
 }
 
 /*
+ * discard an AFS inode
+ */
+int afs_drop_inode(struct inode *inode)
+{
+        _enter("");
+
+        if (test_bit(AFS_VNODE_PSEUDODIR, &AFS_FS_I(inode)->flags))
+                return generic_delete_inode(inode);
+        else
+                return generic_drop_inode(inode);
+}
+
+/*
  * clear an AFS inode
  */
 void afs_evict_inode(struct inode *inode)