ANDROID: sdcardfs: Add option to drop unused dentries

This adds the nocache mount option, which will cause sdcardfs to always
drop dentries that are not in use, preventing cached entries from
holding on to lower dentries, which could  cause strange behavior when
bypassing the sdcardfs layer and directly changing the lower fs.

Change-Id: I70268584a20b989ae8cfdd278a2e4fa1605217fb
Signed-off-by: Daniel Rosenberg <drosen@google.com>

4 files changed, 16 insertions, 0 deletions

diff --git a/fs/sdcardfs/dentry.c b/fs/sdcardfs/dentry.c
index c8f3bcbfb..e941565d3 100755
--- a/fs/sdcardfs/dentry.c
+++ b/fs/sdcardfs/dentry.c
@@ -129,6 +129,12 @@ out:
 	return err;
 }
 
+/* 1 = delete, 0 = cache */
+static int sdcardfs_d_delete(const struct dentry *d)
+{
+	return SDCARDFS_SB(d->d_sb)->options.nocache ? 1 : 0;
+}
+
 static void sdcardfs_d_release(struct dentry *dentry)
 {
 	/* release and reset the lower paths */
@@ -187,6 +193,7 @@ static void sdcardfs_canonical_path(const struct path *path,
 
 const struct dentry_operations sdcardfs_ci_dops = {
 	.d_revalidate	= sdcardfs_d_revalidate,
+	.d_delete	= sdcardfs_d_delete,
 	.d_release	= sdcardfs_d_release,
 	.d_hash	= sdcardfs_hash_ci,
 	.d_compare	= sdcardfs_cmp_ci,
diff --git a/fs/sdcardfs/main.c b/fs/sdcardfs/main.c
index 8a01bebd4..8e12a7dda 100755
--- a/fs/sdcardfs/main.c
+++ b/fs/sdcardfs/main.c
@@ -34,6 +34,7 @@ enum {
 	Opt_reserved_mb,
 	Opt_gid_derivation,
 	Opt_default_normal,
+	Opt_nocache,
 	Opt_err,
 };
 
@@ -48,6 +49,7 @@ static const match_table_t sdcardfs_tokens = {
 	{Opt_gid_derivation, "derive_gid"},
 	{Opt_default_normal, "default_normal"},
 	{Opt_reserved_mb, "reserved_mb=%u"},
+	{Opt_nocache, "nocache"},
 	{Opt_err, NULL}
 };
 
@@ -71,6 +73,7 @@ static int parse_options(struct super_block *sb, char *options, int silent,
 	/* by default, gid derivation is off */
 	opts->gid_derivation = false;
 	opts->default_normal = false;
+	opts->nocache = false;
 
 	*debug = 0;
 
@@ -127,6 +130,9 @@ static int parse_options(struct super_block *sb, char *options, int silent,
 			break;
 		case Opt_default_normal:
 			opts->default_normal = true;
+		case Opt_nocache:
+			opts->nocache = true;
+			break;
 		/* unknown option */
 		default:
 			if (!silent)
diff --git a/fs/sdcardfs/sdcardfs.h b/fs/sdcardfs/sdcardfs.h
index 63279a603..0d94d56c7 100755
--- a/fs/sdcardfs/sdcardfs.h
+++ b/fs/sdcardfs/sdcardfs.h
@@ -196,6 +196,7 @@ struct sdcardfs_mount_options {
 	bool gid_derivation;
 	bool default_normal;
 	unsigned int reserved_mb;
+	bool nocache;
 };
 
 struct sdcardfs_vfsmount_options {
diff --git a/fs/sdcardfs/super.c b/fs/sdcardfs/super.c
index 87d6f8365..9d5407ea3 100755
--- a/fs/sdcardfs/super.c
+++ b/fs/sdcardfs/super.c
@@ -308,6 +308,8 @@ static int sdcardfs_show_options(struct vfsmount *mnt, struct seq_file *m,
 		seq_puts(m, ",default_normal");
 	if (opts->reserved_mb != 0)
 		seq_printf(m, ",reserved=%uMB", opts->reserved_mb);
+	if (opts->nocache)
+		seq_printf(m, ",nocache");
 
 	return 0;
 };