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Subject[PATCH 06/20] afs: Implement @cell substitution handling
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Implement @cell substitution handling such that if @cell is seen as a name
in a dynamic root mount, then the name of the root cell for that network
namespace will be substituted for @cell during lookup.

The substitution of @cell for the current net namespace is set by writing
the cell name to /proc/fs/afs/rootcell. The value can be obtained by
reading the file.

For example:

# mount -t afs none /kafs -o dyn
# echo grand.central.org >/proc/fs/afs/rootcell
# ls /kafs/@cell
archive/ cvs/ doc/ local/ project/ service/ software/ user/ www/
# cat /proc/fs/afs/rootcell
grand.central.org

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

fs/afs/cell.c | 2 ++
fs/afs/dir.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/afs/proc.c | 35 ++++++++++++++++++++++++++++++++-
3 files changed, 96 insertions(+), 1 deletion(-)

diff --git a/fs/afs/cell.c b/fs/afs/cell.c
index 721425b98b31..fdf4c36cff79 100644
--- a/fs/afs/cell.c
+++ b/fs/afs/cell.c
@@ -130,6 +130,8 @@ static struct afs_cell *afs_alloc_cell(struct afs_net *net,
_leave(" = -ENAMETOOLONG");
return ERR_PTR(-ENAMETOOLONG);
}
+ if (namelen == 5 && memcmp(name, "@cell", 5) == 0)
+ return ERR_PTR(-EINVAL);

_enter("%*.*s,%s", namelen, namelen, name, vllist);

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 9bac606725ee..4f5e5c15ed6f 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -921,6 +921,62 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
return NULL;
}

+/*
+ * Look up @cell in a dynroot directory. This is a substitution for the
+ * local cell name for the net namespace.
+ */
+static struct dentry *afs_lookup_atcell(struct dentry *dentry)
+{
+ struct afs_cell *cell;
+ struct afs_net *net = afs_d2net(dentry);
+ struct dentry *parent, *ret;
+ unsigned int seq = 0;
+ char *name;
+ int len;
+
+ if (!net->ws_cell)
+ return ERR_PTR(-ENOENT);
+
+ parent = dget_parent(dentry);
+
+ ret = ERR_PTR(-ENOMEM);
+ name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
+ if (!name)
+ goto out_p;
+
+ rcu_read_lock();
+ do {
+ read_seqbegin_or_lock(&net->cells_lock, &seq);
+ cell = rcu_dereference_raw(net->ws_cell);
+ if (cell) {
+ len = cell->name_len;
+ memcpy(name, cell->name, len + 1);
+ }
+ } while (need_seqretry(&net->cells_lock, seq));
+ done_seqretry(&net->cells_lock, seq);
+ rcu_read_unlock();
+
+ ret = ERR_PTR(-ENOENT);
+ if (!cell)
+ goto out_n;
+
+ ret = lookup_one_len(name, parent, len);
+ if (IS_ERR(ret) || d_is_positive(ret))
+ goto out_n;
+
+ /* We don't want to d_add() the @cell dentry here as we don't want to
+ * the cached dentry to hide changes to the local cell name.
+ */
+ dput(ret);
+ ret = NULL;
+
+out_n:
+ kfree(name);
+out_p:
+ dput(parent);
+ return ret;
+}
+
/*
* Look up an entry in a dynroot directory.
*/
@@ -942,6 +998,10 @@ static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentr
return ERR_PTR(-ENAMETOOLONG);
}

+ if (dentry->d_name.len == 5 &&
+ memcmp(dentry->d_name.name, "@cell", 5) == 0)
+ return afs_lookup_atcell(dentry);
+
inode = afs_try_auto_mntpt(dentry, dir);
if (IS_ERR(inode)) {
ret = PTR_ERR(inode);
diff --git a/fs/afs/proc.c b/fs/afs/proc.c
index 7e9d6b2f9734..f28719c8d153 100644
--- a/fs/afs/proc.c
+++ b/fs/afs/proc.c
@@ -334,7 +334,40 @@ static ssize_t afs_proc_cells_write(struct file *file, const char __user *buf,
static ssize_t afs_proc_rootcell_read(struct file *file, char __user *buf,
size_t size, loff_t *_pos)
{
- return 0;
+ struct afs_cell *cell;
+ struct afs_net *net = afs_proc2net(file);
+ unsigned int seq = 0;
+ char name[AFS_MAXCELLNAME + 1];
+ int len;
+
+ if (*_pos > 0)
+ return 0;
+ if (!net->ws_cell)
+ return 0;
+
+ rcu_read_lock();
+ do {
+ read_seqbegin_or_lock(&net->cells_lock, &seq);
+ len = 0;
+ cell = rcu_dereference_raw(net->ws_cell);
+ if (cell) {
+ len = cell->name_len;
+ memcpy(name, cell->name, len);
+ }
+ } while (need_seqretry(&net->cells_lock, seq));
+ done_seqretry(&net->cells_lock, seq);
+ rcu_read_unlock();
+
+ if (!len)
+ return 0;
+
+ name[len++] = '\n';
+ if (len > size)
+ len = size;
+ if (copy_to_user(buf, name, len) != 0)
+ return -EFAULT;
+ *_pos = 1;
+ return len;
}

/*
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