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, 55 insertions, 23 deletions

diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c
index a9e23039ea34..6d552686c498 100644
--- a/fs/afs/mntpt.c
+++ b/fs/afs/mntpt.c
@@ -38,6 +38,11 @@ const struct inode_operations afs_mntpt_inode_operations = {
         .getattr        = afs_getattr,
 };
 
+const struct inode_operations afs_autocell_inode_operations = {
+        .follow_link    = afs_mntpt_follow_link,
+        .getattr        = afs_getattr,
+};
+
 static LIST_HEAD(afs_vfsmounts);
 static DECLARE_DELAYED_WORK(afs_mntpt_expiry_timer, afs_mntpt_expiry_timed_out);
 
@@ -136,20 +141,16 @@ static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
 {
         struct afs_super_info *super;
         struct vfsmount *mnt;
+        struct afs_vnode *vnode;
         struct page *page;
-        size_t size;
-        char *buf, *devname, *options;
+        char *devname, *options;
+        bool rwpath = false;
         int ret;
 
         _enter("{%s}", mntpt->d_name.name);
 
         BUG_ON(!mntpt->d_inode);
 
-        ret = -EINVAL;
-        size = mntpt->d_inode->i_size;
-        if (size > PAGE_SIZE - 1)
-                goto error_no_devname;
-
         ret = -ENOMEM;
         devname = (char *) get_zeroed_page(GFP_KERNEL);
         if (!devname)
@@ -159,28 +160,59 @@ static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
         if (!options)
                 goto error_no_options;
 
-        /* read the contents of the AFS special symlink */
-        page = read_mapping_page(mntpt->d_inode->i_mapping, 0, NULL);
-        if (IS_ERR(page)) {
-                ret = PTR_ERR(page);
-                goto error_no_page;
+        vnode = AFS_FS_I(mntpt->d_inode);
+        if (test_bit(AFS_VNODE_PSEUDODIR, &vnode->flags)) {
+                /* if the directory is a pseudo directory, use the d_name */
+                static const char afs_root_cell[] = ":root.cell.";
+                unsigned size = mntpt->d_name.len;
+
+                ret = -ENOENT;
+                if (size < 2 || size > AFS_MAXCELLNAME)
+                        goto error_no_page;
+
+                if (mntpt->d_name.name[0] == '.') {
+                        devname[0] = '#';
+                        memcpy(devname + 1, mntpt->d_name.name, size - 1);
+                        memcpy(devname + size, afs_root_cell,
+                               sizeof(afs_root_cell));
+                        rwpath = true;
+                } else {
+                        devname[0] = '%';
+                        memcpy(devname + 1, mntpt->d_name.name, size);
+                        memcpy(devname + size + 1, afs_root_cell,
+                               sizeof(afs_root_cell));
+                }
+        } else {
+                /* read the contents of the AFS special symlink */
+                loff_t size = i_size_read(mntpt->d_inode);
+                char *buf;
+
+                ret = -EINVAL;
+                if (size > PAGE_SIZE - 1)
+                        goto error_no_page;
+
+                page = read_mapping_page(mntpt->d_inode->i_mapping, 0, NULL);
+                if (IS_ERR(page)) {
+                        ret = PTR_ERR(page);
+                        goto error_no_page;
+                }
+
+                ret = -EIO;
+                if (PageError(page))
+                        goto error;
+
+                buf = kmap_atomic(page, KM_USER0);
+                memcpy(devname, buf, size);
+                kunmap_atomic(buf, KM_USER0);
+                page_cache_release(page);
+                page = NULL;
         }
 
-        ret = -EIO;
-        if (PageError(page))
-                goto error;
-
-        buf = kmap_atomic(page, KM_USER0);
-        memcpy(devname, buf, size);
-        kunmap_atomic(buf, KM_USER0);
-        page_cache_release(page);
-        page = NULL;
-
         /* work out what options we want */
         super = AFS_FS_S(mntpt->d_sb);
         memcpy(options, "cell=", 5);
         strcpy(options + 5, super->volume->cell->name);
-        if (super->volume->type == AFSVL_RWVOL)
+        if (super->volume->type == AFSVL_RWVOL || rwpath)
                 strcat(options, ",rwpath");
 
         /* try and do the mount */