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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>
This commit is contained in:
David Howells 2018-04-06 14:17:23 +01:00
parent 6f8880d8e6
commit 37ab636880
3 changed files with 89 additions and 1 deletions
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2
fs/afs/cell.c
View file

@ -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);

53
fs/afs/dir.c
View file

@ -908,6 +908,55 @@ success:
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 *ret;
unsigned int seq = 0;
char *name;
int len;
if (!net->ws_cell)
return ERR_PTR(-ENOENT);
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, dentry->d_parent, len);
/* 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.
*/
out_n:
kfree(name);
out_p:
return ret;
}
/*
* Look up an entry in a dynroot directory.
*/
@ -929,6 +978,10 @@ 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);

35
fs/afs/proc.c
View file

@ -334,7 +334,40 @@ inval:
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;
}
/*