Cc: <serue@...>, <matthltc@...>, Eric W. Biederman <ebiederm@...>, <hpa@...>, Pavel Emelyanov <xemul@...>, Containers <containers@...>, <linux-kernel@...>
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject:[PATCH 4/4]: Enable multiple mounts of /dev/pts
To support multiple PTY namespaces, allow multiple mounts of /dev/pts, once
within each PTY namespace.
This patch removes the get_sb_single() in devpts_get_sb() and uses test and
set sb interfaces to allow remounting /dev/pts.
Changelog [v4]:
- Split-off the simpler changes of moving global=variables into
'pts_namespace' to previous patch.
Changelog [v3]:
- Removed some unnecessary comments from devpts_set_sb()
Changelog [v2]:
- (Pavel Emelianov/Serge Hallyn) Remove reference to pts_ns from
sb->s_fs_info to fix the circular reference (/dev/pts is not
unmounted unless the pts_ns is destroyed, so we don't need a
reference to the pts_ns).
Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
---
fs/devpts/inode.c | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 59 insertions(+), 3 deletions(-)
Index: 2.6.25-rc8-mm1/fs/devpts/inode.c
===================================================================
--- 2.6.25-rc8-mm1.orig/fs/devpts/inode.c 2008-04-12 10:10:33.000000000 -0700
+++ 2.6.25-rc8-mm1/fs/devpts/inode.c 2008-04-12 10:10:38.000000000 -0700
@@ -154,17 +154,73 @@ fail:
return -ENOMEM;
}
+/*
+ * We use test and set super-block operations to help determine whether we
+ * need a new super-block for this namespace. get_sb() walks the list of
+ * existing devpts supers, comparing them with the @data ptr. Since we
+ * passed 'current's namespace as the @data pointer we can compare the
+ * namespace pointer in the super-block's 's_fs_info'. If the test is
+ * TRUE then get_sb() returns a new active reference to the super block.
+ * Otherwise, it helps us build an active reference to a new one.
+ */
+
+static int devpts_test_sb(struct super_block *sb, void *data)
+{
+ return sb->s_fs_info == data;
+}
+
+static int devpts_set_sb(struct super_block *sb, void *data)
+{
+ sb->s_fs_info = data;
+ return set_anon_super(sb, NULL);
+}
+
static int devpts_get_sb(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
- return get_sb_single(fs_type, flags, data, devpts_fill_super, mnt);
+ struct super_block *sb;
+ struct pts_namespace *ns;
+ int err;
+
+ /* hereafter we're very similar to proc_get_sb */
+ if (flags & MS_KERNMOUNT)
+ ns = data;
+ else
+ ns = &init_pts_ns;
+
+ /* hereafter we're very simlar to get_sb_nodev */
+ sb = sget(fs_type, devpts_test_sb, devpts_set_sb, ns);
+ if (IS_ERR(sb))
+ return PTR_ERR(sb);
+
+ if (sb->s_root)
+ return simple_set_mnt(mnt, sb);
+
+ sb->s_flags = flags;
+ err = devpts_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
+ if (err) {
+ up_write(&sb->s_umount);
+ deactivate_super(sb);
+ return err;
+ }
+
+ sb->s_flags |= MS_ACTIVE;
+ ns->mnt = mnt;
+
+ return simple_set_mnt(mnt, sb);
+}
+
+static void devpts_kill_sb(struct super_block *sb)
+{
+ sb->s_fs_info = NULL;
+ kill_anon_super(sb);
}
static struct file_system_type devpts_fs_type = {
.owner = THIS_MODULE,
.name = "devpts",
.get_sb = devpts_get_sb,
- .kill_sb = kill_anon_super,
+ .kill_sb = devpts_kill_sb,
};
/*
@@ -315,7 +371,7 @@ static int __init init_devpts_fs(void)
err = register_filesystem(&devpts_fs_type);
if (!err) {
- mnt = kern_mount(&devpts_fs_type);
+ mnt = kern_mount_data(&devpts_fs_type, &init_pts_ns);
if (IS_ERR(mnt))
err = PTR_ERR(mnt);
else
--
