[PATCH V3 6/6] erofs: Support sharing cookies in the same domain

[Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>]

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>
---
 fs/erofs/fscache.c  | 89 +++++++++++++++++++++++++++++++++++++++++++--
 fs/erofs/internal.h |  4 +-
 2 files changed, 89 insertions(+), 4 deletions(-)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 4e0a441afb7d..e9ae1ee963e2 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;
 
@@ -504,7 +505,6 @@ static int erofs_fscache_init_domain(struct super_block *sb)
 
 	domain->volume = sbi->volume;
 	refcount_set(&domain->ref, 1);
-	mutex_init(&domain->mutex);
 	list_add(&domain->list, &erofs_domain_list);
 	return 0;
 out:
@@ -534,8 +534,8 @@ 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)
+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;
@@ -585,13 +585,96 @@ struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
 	return ERR_PTR(ret);
 }
 
+static
+struct erofs_fscache *erofs_fscache_domain_init_cookie(struct super_block *sb,
+							char *name, bool need_inode)
+{
+	struct inode *inode;
+	struct erofs_fscache *ctx;
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+	struct erofs_domain *domain = sbi->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)
+		return ERR_PTR(-ENOMEM);
+
+	inode = new_inode(erofs_pseudo_mnt->mnt_sb);
+	if (!inode) {
+		kfree(ctx->name);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	ctx->domain = domain;
+	ctx->anon_inode = inode;
+	inode->i_private = ctx;
+	erofs_fscache_domain_get(domain);
+	return ctx;
+}
+
+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_sb_info *sbi = EROFS_SB(sb);
+	struct erofs_domain *domain = sbi->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)
+			continue;
+		if (ctx->domain == domain && !strcmp(ctx->name, name)) {
+			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)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+
+	if (sbi->opt.domain_id)
+		return erofs_domain_register_cookie(sb, name, need_inode);
+	else
+		return erofs_fscache_acquire_cookie(sb, name, need_inode);
+}
+
 void erofs_fscache_unregister_cookie(struct erofs_fscache *ctx)
 {
+	struct erofs_domain *domain;
+
 	if (!ctx)
 		return;
+	domain = ctx->domain;
+	if (domain) {
+		mutex_lock(&erofs_domain_cookies_lock);
+		/* Cookie is still in use */
+		if (atomic_read(&ctx->anon_inode->i_count) > 1) {
+			iput(ctx->anon_inode);
+			mutex_unlock(&erofs_domain_cookies_lock);
+			return;
+		}
+		iput(ctx->anon_inode);
+		kfree(ctx->name);
+		mutex_unlock(&erofs_domain_cookies_lock);
+	}
 
 	fscache_unuse_cookie(ctx->cookie, NULL, NULL);
 	fscache_relinquish_cookie(ctx->cookie, false);
+	erofs_fscache_domain_put(domain);
 	ctx->cookie = NULL;
 
 	iput(ctx->inode);
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 4dd0b545755a..8a6f94b27a23 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -101,7 +101,6 @@ struct erofs_sb_lz4_info {
 
 struct erofs_domain {
 	refcount_t ref;
-	struct mutex mutex;
 	struct list_head list;
 	struct fscache_volume *volume;
 	char *domain_id;
@@ -110,6 +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