[PATCH V6 5/6] erofs: Support sharing cookies in the same domain

[Jia Zhu]

Several erofs filesystems can belong to one domain, and data blobs can
be shared among these erofs filesystems of same domain.

Users could specify domain_id mount option to create or join into a
domain.

Signed-off-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
---
 fs/erofs/fscache.c  | 99 ++++++++++++++++++++++++++++++++++++++++++---
 fs/erofs/internal.h |  3 ++
 2 files changed, 96 insertions(+), 6 deletions(-)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 4a7346b9fa73..ce9301a890f9 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -7,6 +7,7 @@
 #include "internal.h"
 
 static DEFINE_MUTEX(erofs_domain_list_lock);
+static DEFINE_MUTEX(erofs_domain_cookies_lock);
 static LIST_HEAD(erofs_domain_list);
 static struct vfsmount *erofs_pseudo_mnt;
 
@@ -527,8 +528,9 @@ static int erofs_fscache_register_domain(struct super_block *sb)
 	return err;
 }
 
-struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
-						     char *name, bool need_inode)
+static
+struct erofs_fscache *erofs_fscache_acquire_cookie(struct super_block *sb,
+						    char *name, bool need_inode)
 {
 	struct fscache_volume *volume = EROFS_SB(sb)->volume;
 	struct erofs_fscache *ctx;
@@ -577,17 +579,102 @@ struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
 	return ERR_PTR(ret);
 }
 
-void erofs_fscache_unregister_cookie(struct erofs_fscache *ctx)
+static void erofs_fscache_relinquish_cookie(struct erofs_fscache *ctx)
 {
-	if (!ctx)
-		return;
-
 	fscache_unuse_cookie(ctx->cookie, NULL, NULL);
 	fscache_relinquish_cookie(ctx->cookie, false);
 	iput(ctx->inode);
+	kfree(ctx->name);
 	kfree(ctx);
 }
 
+static
+struct erofs_fscache *erofs_fscache_domain_init_cookie(struct super_block *sb,
+							char *name, bool need_inode)
+{
+	int err;
+	struct inode *inode;
+	struct erofs_fscache *ctx;
+	struct erofs_domain *domain = EROFS_SB(sb)->domain;
+
+	ctx = erofs_fscache_acquire_cookie(sb, name, need_inode);
+	if (IS_ERR(ctx))
+		return ctx;
+
+	ctx->name = kstrdup(name, GFP_KERNEL);
+	if (!ctx->name) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	inode = new_inode(erofs_pseudo_mnt->mnt_sb);
+	if (!inode) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	ctx->domain = domain;
+	ctx->anon_inode = inode;
+	inode->i_private = ctx;
+	refcount_inc(&domain->ref);
+	return ctx;
+out:
+	erofs_fscache_relinquish_cookie(ctx);
+	return ERR_PTR(err);
+}
+
+static
+struct erofs_fscache *erofs_domain_register_cookie(struct super_block *sb,
+						    char *name, bool need_inode)
+{
+	struct inode *inode;
+	struct erofs_fscache *ctx;
+	struct erofs_domain *domain = EROFS_SB(sb)->domain;
+	struct super_block *psb = erofs_pseudo_mnt->mnt_sb;
+
+	mutex_lock(&erofs_domain_cookies_lock);
+	list_for_each_entry(inode, &psb->s_inodes, i_sb_list) {
+		ctx = inode->i_private;
+		if (!ctx || ctx->domain != domain || strcmp(ctx->name, name))
+			continue;
+		igrab(inode);
+		mutex_unlock(&erofs_domain_cookies_lock);
+		return ctx;
+	}
+	ctx = erofs_fscache_domain_init_cookie(sb, name, need_inode);
+	mutex_unlock(&erofs_domain_cookies_lock);
+	return ctx;
+}
+
+struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
+						     char *name, bool need_inode)
+{
+	if (EROFS_SB(sb)->opt.domain_id)
+		return erofs_domain_register_cookie(sb, name, need_inode);
+	return erofs_fscache_acquire_cookie(sb, name, need_inode);
+}
+
+void erofs_fscache_unregister_cookie(struct erofs_fscache *ctx)
+{
+	bool drop;
+	struct erofs_domain *domain;
+
+	if (!ctx)
+		return;
+	domain = ctx->domain;
+	if (domain) {
+		mutex_lock(&erofs_domain_cookies_lock);
+		drop = atomic_read(&ctx->anon_inode->i_count) == 1;
+		iput(ctx->anon_inode);
+		mutex_unlock(&erofs_domain_cookies_lock);
+		if (!drop)
+			return;
+	}
+
+	erofs_fscache_relinquish_cookie(ctx);
+	erofs_fscache_domain_put(domain);
+}
+
 int erofs_fscache_register_fs(struct super_block *sb)
 {
 	int ret;
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 273fb35170e2..0f63830c9056 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -109,6 +109,9 @@ struct erofs_domain {
 struct erofs_fscache {
 	struct fscache_cookie *cookie;
 	struct inode *inode;
+	struct inode *anon_inode;
+	struct erofs_domain *domain;
+	char *name;
 };
 
 struct erofs_sb_info {
-- 
2.20.1