linux-kernel - [PATCH 2/4] fs - add have_local

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Date:   Wed, 14 Sep 2016 14:14:40 +0800
From:   Ian Kent <raven@...maw.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     autofs mailing list <autofs@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...IV.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Omar Sandoval <osandov@...ndov.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 2/4] fs - add have_local_submounts()

The have_submounts() function checks if a dentry is a mountpoint
in any namespace but autofs needs to know if the dentry is a
mountpoint within the current namespace.

Add have_local_submounts() to to do this.

Signed-off-by: Ian Kent <raven@...maw.net>
Cc: Al Viro <viro@...IV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@...ssion.com>
Cc: Omar Sandoval <osandov@...ndov.com>
---
 fs/dcache.c            |   34 ++++++++++++++++++++++++++++++++++
 include/linux/dcache.h |    1 +
 2 files changed, 35 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 5c7cc95..218166b 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1307,6 +1307,40 @@ int have_submounts(struct dentry *parent)
 EXPORT_SYMBOL(have_submounts);
 
 /*
+ * Search for at least 1 mount point in the dentry's subdirs.
+ * We descend to the next level whenever the d_subdirs
+ * list is non-empty and continue searching.
+ */
+
+static enum d_walk_ret check_local_mount(void *data, struct dentry *dentry)
+{
+	int *ret = data;
+	if (is_local_mountpoint(dentry)) {
+		*ret = 1;
+		return D_WALK_QUIT;
+	}
+	return D_WALK_CONTINUE;
+}
+
+/**
+ * have_local_submounts - check for mounts over a dentry
+ * 			  in the current namespace
+ * @parent: dentry to check.
+ *
+ * Return true if the parent or its subdirectories contain
+ * a mount point
+ */
+int have_local_submounts(struct dentry *parent)
+{
+	int ret = 0;
+
+	d_walk(parent, &ret, check_local_mount, NULL);
+
+	return ret;
+}
+EXPORT_SYMBOL(have_local_submounts);
+
+/*
  * Called by mount code to set a mountpoint and check if the mountpoint is
  * reachable (e.g. NFS can unhash a directory dentry and then the complete
  * subtree can become unreachable).
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 5ff3e9a..796b358 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -255,6 +255,7 @@ extern void d_prune_aliases(struct inode *);
 
 /* test whether we have any submounts in a subdir tree */
 extern int have_submounts(struct dentry *);
+extern int have_local_submounts(struct dentry *);
 
 /*
  * This adds the entry to the hash queues.