commit 12064f3a794e67c81d2bae15606f03f436630e88
author Daniel Rosenberg <drosen@google.com> Fri Jul 06 16:24:27 2018 -0700
committer Daniel Rosenberg <drosen@google.com> Fri Nov 02 22:03:28 2018 +0000
tree 58b39743d7b7817f1d8a1d91ee108e0aea799691
parent 4ed22187defde44f5c49a4e09e478867c84892e5

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>

fs/sdcardfs/dentry.c

diff --git a/fs/sdcardfs/dentry.c b/fs/sdcardfs/dentry.c
index 776d549..cb573f1 100644
--- a/fs/sdcardfs/dentry.c
+++ b/fs/sdcardfs/dentry.c
@@ -123,6 +123,12 @@
 	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)
 {
 	if (!dentry || !dentry->d_fsdata)
@@ -181,6 +187,7 @@
 
 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,

fs/sdcardfs/main.c

diff --git a/fs/sdcardfs/main.c b/fs/sdcardfs/main.c
index 27ec726..ba52af8 100644
--- a/fs/sdcardfs/main.c
+++ b/fs/sdcardfs/main.c
@@ -34,6 +34,7 @@
 	Opt_reserved_mb,
 	Opt_gid_derivation,
 	Opt_default_normal,
+	Opt_nocache,
 	Opt_err,
 };
 
@@ -48,6 +49,7 @@
 	{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 @@
 	/* by default, gid derivation is off */
 	opts->gid_derivation = false;
 	opts->default_normal = false;
+	opts->nocache = false;
 
 	*debug = 0;
 
@@ -128,6 +131,9 @@
 		case Opt_default_normal:
 			opts->default_normal = true;
 			break;
+		case Opt_nocache:
+			opts->nocache = true;
+			break;
 		/* unknown option */
 		default:
 			if (!silent)

fs/sdcardfs/sdcardfs.h

diff --git a/fs/sdcardfs/sdcardfs.h b/fs/sdcardfs/sdcardfs.h
index ec2290a..c2a16a0 100644
--- a/fs/sdcardfs/sdcardfs.h
+++ b/fs/sdcardfs/sdcardfs.h
@@ -198,6 +198,7 @@
 	bool gid_derivation;
 	bool default_normal;
 	unsigned int reserved_mb;
+	bool nocache;
 };
 
 struct sdcardfs_vfsmount_options {

fs/sdcardfs/super.c

diff --git a/fs/sdcardfs/super.c b/fs/sdcardfs/super.c
index cffcdb1..140696e 100644
--- a/fs/sdcardfs/super.c
+++ b/fs/sdcardfs/super.c
@@ -311,6 +311,8 @@
 		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;
 };