[PATCH V4 4/6] erofs: introduce a pseudo mnt to manage shared cookies

[Jia Zhu <zhujia.zj@bytedance.com>]

Use a pseudo mnt to manage shared cookies.

Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
---
 fs/erofs/fscache.c  | 13 +++++++++++++
 fs/erofs/internal.h |  1 +
 fs/erofs/super.c    | 31 +++++++++++++++++++++++++++++--
 3 files changed, 43 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 10d3f0511f15..ff8382df493e 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -8,6 +8,7 @@
 
 static DEFINE_MUTEX(erofs_domain_list_lock);
 static LIST_HEAD(erofs_domain_list);
+static struct vfsmount *erofs_pseudo_mnt;
 
 static struct netfs_io_request *erofs_fscache_alloc_request(struct address_space *mapping,
 					     loff_t start, size_t len)
@@ -429,6 +430,10 @@ static void erofs_fscache_domain_put(struct erofs_domain *domain)
 	if (refcount_dec_and_test(&domain->ref)) {
 		list_del(&domain->list);
 		fscache_relinquish_volume(domain->volume, NULL, false);
+		if (list_empty(&erofs_domain_list)) {
+			kern_unmount(erofs_pseudo_mnt);
+			erofs_pseudo_mnt = NULL;
+		}
 		mutex_unlock(&erofs_domain_list_lock);
 		kfree(domain->domain_id);
 		kfree(domain);
@@ -482,6 +487,14 @@ static int erofs_fscache_init_domain(struct super_block *sb)
 	if (err)
 		goto out;
 
+	if (!erofs_pseudo_mnt) {
+		erofs_pseudo_mnt = kern_mount(&erofs_fs_type);
+		if (IS_ERR(erofs_pseudo_mnt)) {
+			err = PTR_ERR(erofs_pseudo_mnt);
+			goto out;
+		}
+	}
+
 	domain->volume = sbi->volume;
 	refcount_set(&domain->ref, 1);
 	list_add(&domain->list, &erofs_domain_list);
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 7f0939f4005b..88c1a46867b3 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -402,6 +402,7 @@ struct page *erofs_grab_cache_page_nowait(struct address_space *mapping,
 }
 
 extern const struct super_operations erofs_sops;
+extern struct file_system_type erofs_fs_type;
 
 extern const struct address_space_operations erofs_raw_access_aops;
 extern const struct address_space_operations z_erofs_aops;
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 79e871c04fe2..24bac58285e8 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -676,6 +676,13 @@ static const struct export_operations erofs_export_ops = {
 	.get_parent = erofs_get_parent,
 };
 
+static int erofs_fc_fill_pseudo_super(struct super_block *sb, struct fs_context *fc)
+{
+	static const struct tree_descr empty_descr = {""};
+
+	return simple_fill_super(sb, EROFS_SUPER_MAGIC, &empty_descr);
+}
+
 static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	struct inode *inode;
@@ -776,6 +783,11 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 	return 0;
 }
 
+static int erofs_fc_anon_get_tree(struct fs_context *fc)
+{
+	return get_tree_nodev(fc, erofs_fc_fill_pseudo_super);
+}
+
 static int erofs_fc_get_tree(struct fs_context *fc)
 {
 	struct erofs_fs_context *ctx = fc->fs_private;
@@ -844,10 +856,20 @@ static const struct fs_context_operations erofs_context_ops = {
 	.free		= erofs_fc_free,
 };
 
+static const struct fs_context_operations erofs_anon_context_ops = {
+	.get_tree       = erofs_fc_anon_get_tree,
+};
+
 static int erofs_init_fs_context(struct fs_context *fc)
 {
-	struct erofs_fs_context *ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
+	struct erofs_fs_context *ctx;
+
+	if (fc->sb_flags & SB_KERNMOUNT) {
+		fc->ops = &erofs_anon_context_ops;
+		return 0;
+	}
 
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
 	ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
@@ -874,6 +896,11 @@ static void erofs_kill_sb(struct super_block *sb)
 
 	WARN_ON(sb->s_magic != EROFS_SUPER_MAGIC);
 
+	if (sb->s_flags & SB_KERNMOUNT) {
+		kill_litter_super(sb);
+		return;
+	}
+
 	if (erofs_is_fscache_mode(sb))
 		kill_anon_super(sb);
 	else
@@ -908,7 +935,7 @@ static void erofs_put_super(struct super_block *sb)
 	sbi->s_fscache = NULL;
 }
 
-static struct file_system_type erofs_fs_type = {
+struct file_system_type erofs_fs_type = {
 	.owner          = THIS_MODULE,
 	.name           = "erofs",
 	.init_fs_context = erofs_init_fs_context,
-- 
2.20.1