[PATCH 14/75] Define get_init_pts_sb()

Alan Cox
2009-01-02T13:42:05Z

From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>

See comments in the function header for details. The new interface will
be used in a follow-on patch.

Changelog [v2]:
[Dave Hansen] Replace get_sb_ref() in fs/super.c with get_init_pts_sb()
and make the new interface private to devpts

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Alan Cox <alan@redhat.com>
---

fs/devpts/inode.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 files changed, 54 insertions(+), 1 deletions(-)

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 8ee9dc2..2d0eb2c 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -305,10 +305,63 @@ fail:
return -ENOMEM;
}

+static int compare_init_pts_sb(struct super_block *s, void *p)
+{
+ if (devpts_mnt)
+ return devpts_mnt->mnt_sb == s;
+
+ return 0;
+}
+
+/*
+ * get_init_pts_sb()
+ *
+ * This interface is needed to support multiple namespace semantics in
+ * devpts while preserving backward compatibility of the current 'single-
+ * namespace' semantics. i.e all mounts of devpts without the 'newinstance'
+ * mount option should bind to the initial kernel mount, like
+ * get_sb_single().
+ *
+ * Mounts with 'newinstance' option create a new private namespace.
+ *
+ * But for single-mount semantics, devpts cannot use get_sb_single(),
+ * because get_sb_single()/sget() find and use the super-block from
+ * the most recent mount of devpts. But that recent mount may be a
+ * 'newinstance' mount and get_sb_single() would pick the newinstance
+ * super-block instead of the initial super-block.
+ *
+ * This interface is identical to get_sb_single() except that it
+ * consistently selects the 'single-namespace' superblock even in the
+ * presence of the private namespace (i.e 'newinstance') super-blocks.
+ */
+static int get_init_pts_sb(struct file_system_type *fs_type, int flags,
+ void *data, struct vfsmount *mnt)
+{
+ struct super_block *s;
+ int error;
+
+ s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
+ if (IS_ERR(s))
+ return PTR_ERR(s);
+
+ if (!s->s_root) {
+ s->s_flags = flags;
+ error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
+ if (error) {
+ up_write(&s->s_umount);
+ deactivate_super(s);
+ return error;
+ }
+ s->s_flags |= MS_ACTIVE;
+ }
+ do_remount_sb(s, flags, data, 0);
+ return simple_set_mnt(mnt, s);
+}
+
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);
+ return get_init_pts_sb(fs_type, flags, data, mnt);
}

static void devpts_kill_sb(struct super_block *sb)