[RFC PATCH 5/5] erofs: support fscache based shared 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 at bytedance.com>
---
 fs/erofs/domain.c   | 60 +++++++++++++++++++++++++++++++++++++++++++++
 fs/erofs/fscache.c  |  7 ++++++
 fs/erofs/internal.h | 13 ++++++++++
 fs/erofs/super.c    | 10 ++++++--
 4 files changed, 88 insertions(+), 2 deletions(-)

diff --git a/fs/erofs/domain.c b/fs/erofs/domain.c
index 6461e4ee3582..ea7b591b7db1 100644
--- a/fs/erofs/domain.c
+++ b/fs/erofs/domain.c
@@ -13,6 +13,66 @@
 static DEFINE_SPINLOCK(erofs_domain_list_lock);
 static LIST_HEAD(erofs_domain_list);
 
+static int erofs_fscache_domain_init_cookie(struct super_block *sb,
+		struct erofs_fscache **fscache, char *name, bool need_inode)
+{
+	int ret;
+	struct inode *inode;
+	struct erofs_fscache *ctx;
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+	struct erofs_domain *domain = sbi->domain;
+
+	ret = erofs_fscache_register_cookie(sb, &ctx, name, need_inode);
+	if (ret)
+		return ret;
+
+	ctx->name = kstrdup(name, GFP_KERNEL);
+	if (!ctx->name)
+		return -ENOMEM;
+
+	inode = new_inode(domain->mnt->mnt_sb);
+	if (!inode) {
+		kfree(ctx->name);
+		return -ENOMEM;
+	}
+
+	ctx->domain = domain;
+	ctx->anon_inode = inode;
+	inode->i_private = ctx;
+	refcount_set(&ctx->ref, 1);
+	erofs_fscache_domain_get(domain);
+	*fscache = ctx;
+	return 0;
+}
+
+int erofs_domain_register_cookie(struct super_block *sb,
+	struct erofs_fscache **fscache, char *name, bool need_inode)
+{
+	int err;
+	struct inode *inode;
+	struct erofs_fscache *ctx;
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+	struct erofs_domain *domain = sbi->domain;
+	struct super_block *psb = domain->mnt->mnt_sb;
+
+	mutex_lock(&domain->mutex);
+	list_for_each_entry(inode, &psb->s_inodes, i_sb_list) {
+		ctx = inode->i_private;
+		if (!ctx)
+			continue;
+		if (!strcmp(ctx->name, name)) {
+			*fscache = ctx;
+			refcount_inc(&ctx->ref);
+			mutex_unlock(&domain->mutex);
+			return 0;
+		}
+	}
+	err = erofs_fscache_domain_init_cookie(sb, fscache, name, need_inode);
+	mutex_unlock(&domain->mutex);
+
+	return err;
+}
+
 void erofs_fscache_domain_get(struct erofs_domain *domain)
 {
 	if (!domain)
diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 5c918a06ae9a..51425e310e3d 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -476,6 +476,8 @@ void erofs_fscache_unregister_cookie(struct erofs_fscache **fscache)
 
 	if (!ctx)
 		return;
+	if (ctx->domain && !refcount_dec_and_test(&ctx->ref))
+		return;
 
 	fscache_unuse_cookie(ctx->cookie, NULL, NULL);
 	fscache_relinquish_cookie(ctx->cookie, false);
@@ -483,7 +485,12 @@ void erofs_fscache_unregister_cookie(struct erofs_fscache **fscache)
 
 	iput(ctx->inode);
 	ctx->inode = NULL;
+	iput(ctx->anon_inode);
+	ctx->anon_inode = NULL;
+	erofs_fscache_domain_put(ctx->domain);
 
+	kfree(ctx->name);
+	ctx->name = NULL;
 	kfree(ctx);
 	*fscache = NULL;
 }
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index bca4e9c57890..1abdad81bfe3 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -109,8 +109,12 @@ struct erofs_domain {
 };
 
 struct erofs_fscache {
+	refcount_t ref;
 	struct fscache_cookie *cookie;
 	struct inode *inode;
+	struct inode *anon_inode;
+	struct erofs_domain *domain;
+	char *name;
 };
 
 struct erofs_sb_info {
@@ -627,6 +631,9 @@ int erofs_fscache_register_domain(struct super_block *sb);
 int erofs_fscache_register_cookie(struct super_block *sb,
 				  struct erofs_fscache **fscache,
 				  char *name, bool need_inode);
+int erofs_domain_register_cookie(struct super_block *sb,
+				  struct erofs_fscache **fscache,
+				  char *name, bool need_inode);
 void erofs_fscache_unregister_cookie(struct erofs_fscache **fscache);
 
 extern const struct address_space_operations erofs_fscache_access_aops;
@@ -648,6 +655,12 @@ static inline int erofs_fscache_register_cookie(struct super_block *sb,
 {
 	return -EOPNOTSUPP;
 }
+static inline int erofs_domain_register_cookie(struct super_block *sb,
+						struct erofs_fscache **fscache,
+						char *name, bool need_inode)
+{
+	return -EOPNOTSUPP;
+}
 
 static inline void erofs_fscache_unregister_cookie(struct erofs_fscache **fscache)
 {
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index bbc63b7d546c..aefe7dfcd4c9 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -245,8 +245,12 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
 	}
 
 	if (erofs_is_fscache_mode(sb)) {
-		ret = erofs_fscache_register_cookie(sb, &dif->fscache,
-				dif->path, false);
+		if (sbi->opt.domain_id)
+			ret = erofs_domain_register_cookie(sb, &dif->fscache, dif->path,
+					false);
+		else
+			ret = erofs_fscache_register_cookie(sb, &dif->fscache, dif->path,
+					false);
 		if (ret)
 			return ret;
 	} else {
@@ -719,6 +723,8 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 			err = erofs_fscache_register_domain(sb);
 			if (err)
 				return err;
+			err = erofs_domain_register_cookie(sb, &sbi->s_fscache,
+					sbi->opt.fsid, true);
 		} else {
 			err = erofs_fscache_register_fs(sb);
 			if (err)
-- 
2.20.1