A new fscache-based shared domain mode is going to be introduced for
erofs. In which case, same data blobs in same domain will be shared
and reused to reduce on-disk space usage.

As the first step, we use pseudo mnt to manage and maintain domain's
lifecycle.

The implementation of sharing blobs will be introduced in subsequent
patches.

Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
---
 fs/erofs/fscache.c  | 95 ++++++++++++++++++++++++++++++++++++++++++++-
 fs/erofs/internal.h | 18 ++++++++-
 fs/erofs/super.c    | 51 ++++++++++++++++++------
 3 files changed, 149 insertions(+), 15 deletions(-)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 8e01d89c3319..439dd3cc096a 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -1,10 +1,15 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * Copyright (C) 2022, Alibaba Cloud
+ * Copyright (C) 2022, Bytedance Inc. All rights reserved.
  */
 #include <linux/fscache.h>
 #include "internal.h"
 
+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)
 {
@@ -417,6 +422,87 @@ const struct address_space_operations erofs_fscache_access_aops = {
 	.readahead = erofs_fscache_readahead,
 };
 
+static void erofs_fscache_domain_get(struct erofs_domain *domain)
+{
+	if (!domain)
+		return;
+	refcount_inc(&domain->ref);
+}
+
+static void erofs_fscache_domain_put(struct erofs_domain *domain)
+{
+	if (!domain)
+		return;
+	if (refcount_dec_and_test(&domain->ref)) {
+		fscache_relinquish_volume(domain->volume, NULL, false);
+		mutex_lock(&erofs_domain_list_lock);
+		list_del(&domain->list);
+		mutex_unlock(&erofs_domain_list_lock);
+		kfree(domain->domain_id);
+		kfree(domain);
+	}
+}
+
+static int erofs_fscache_init_domain(struct super_block *sb)
+{
+	int err;
+	struct erofs_domain *domain;
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+
+	domain = kzalloc(sizeof(struct erofs_domain), GFP_KERNEL);
+	if (!domain)
+		return -ENOMEM;
+
+	domain->domain_id = kstrdup(sbi->opt.domain_id, GFP_KERNEL);
+	if (!domain->domain_id) {
+		kfree(domain);
+		return -ENOMEM;
+	}
+	sbi->domain = domain;
+	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;
+		}
+	}
+	err = erofs_fscache_register_fs(sb);
+	if (err)
+		goto out;
+
+	domain->volume = sbi->volume;
+	refcount_set(&domain->ref, 1);
+	mutex_init(&domain->mutex);
+	list_add(&domain->list, &erofs_domain_list);
+	return 0;
+out:
+	kfree(domain->domain_id);
+	kfree(domain);
+	sbi->domain = NULL;
+	return err;
+}
+
+int erofs_fscache_register_domain(struct super_block *sb)
+{
+	int err;
+	struct erofs_domain *domain;
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+
+	mutex_lock(&erofs_domain_list_lock);
+	list_for_each_entry(domain, &erofs_domain_list, list) {
+		if (!strcmp(domain->domain_id, sbi->opt.domain_id)) {
+			erofs_fscache_domain_get(domain);
+			sbi->domain = domain;
+			sbi->volume = domain->volume;
+			mutex_unlock(&erofs_domain_list_lock);
+			return 0;
+		}
+	}
+	err = erofs_fscache_init_domain(sb);
+	mutex_unlock(&erofs_domain_list_lock);
+	return err;
+}
+
 int erofs_fscache_register_cookie(struct super_block *sb,
 				  struct erofs_fscache **fscache,
 				  char *name, bool need_inode)
@@ -495,7 +581,8 @@ int erofs_fscache_register_fs(struct super_block *sb)
 	char *name;
 	int ret = 0;
 
-	name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
+	name = kasprintf(GFP_KERNEL, "erofs,%s",
+			sbi->domain ? sbi->domain->domain_id : sbi->opt.fsid);
 	if (!name)
 		return -ENOMEM;
 
@@ -515,6 +602,10 @@ void erofs_fscache_unregister_fs(struct super_block *sb)
 {
 	struct erofs_sb_info *sbi = EROFS_SB(sb);
 
-	fscache_relinquish_volume(sbi->volume, NULL, false);
+	if (sbi->domain)
+		erofs_fscache_domain_put(sbi->domain);
+	else
+		fscache_relinquish_volume(sbi->volume, NULL, false);
 	sbi->volume = NULL;
+	sbi->domain = NULL;
 }
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index fe435d077f1a..2790c93ffb83 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -99,6 +99,14 @@ struct erofs_sb_lz4_info {
 	u16 max_pclusterblks;
 };
 
+struct erofs_domain {
+	refcount_t ref;
+	struct mutex mutex;
+	struct list_head list;
+	struct fscache_volume *volume;
+	char *domain_id;
+};
+
 struct erofs_fscache {
 	struct fscache_cookie *cookie;
 	struct inode *inode;
@@ -158,6 +166,7 @@ struct erofs_sb_info {
 	/* fscache support */
 	struct fscache_volume *volume;
 	struct erofs_fscache *s_fscache;
+	struct erofs_domain *domain;
 };
 
 #define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info)
@@ -394,6 +403,7 @@ 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;
@@ -610,6 +620,7 @@ static inline int z_erofs_load_lzma_config(struct super_block *sb,
 #ifdef CONFIG_EROFS_FS_ONDEMAND
 int erofs_fscache_register_fs(struct super_block *sb);
 void erofs_fscache_unregister_fs(struct super_block *sb);
+int erofs_fscache_register_domain(struct super_block *sb);
 
 int erofs_fscache_register_cookie(struct super_block *sb,
 				  struct erofs_fscache **fscache,
@@ -620,10 +631,15 @@ extern const struct address_space_operations erofs_fscache_access_aops;
 #else
 static inline int erofs_fscache_register_fs(struct super_block *sb)
 {
-	return 0;
+	return -EOPNOTSUPP;
 }
 static inline void erofs_fscache_unregister_fs(struct super_block *sb) {}
 
+static inline int erofs_fscache_register_domain(const struct super_block *sb)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int erofs_fscache_register_cookie(struct super_block *sb,
 						struct erofs_fscache **fscache,
 						char *name, bool need_inode)
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index d01109069c6b..69de1731f454 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -688,6 +688,13 @@ 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;
@@ -715,12 +722,17 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 		sb->s_blocksize = EROFS_BLKSIZ;
 		sb->s_blocksize_bits = LOG_BLOCK_SIZE;
 
-		err = erofs_fscache_register_fs(sb);
-		if (err)
-			return err;
-
-		err = erofs_fscache_register_cookie(sb, &sbi->s_fscache,
-						    sbi->opt.fsid, true);
+		if (sbi->opt.domain_id) {
+			err = erofs_fscache_register_domain(sb);
+			if (err)
+				return err;
+		} else {
+			err = erofs_fscache_register_fs(sb);
+			if (err)
+				return err;
+			err = erofs_fscache_register_cookie(sb, &sbi->s_fscache,
+					sbi->opt.fsid, true);
+		}
 		if (err)
 			return err;
 
@@ -798,8 +810,12 @@ static int erofs_fc_get_tree(struct fs_context *fc)
 {
 	struct erofs_fs_context *ctx = fc->fs_private;
 
-	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->opt.fsid)
-		return get_tree_nodev(fc, erofs_fc_fill_super);
+	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND)) {
+		if (!ctx && fc->sb_flags & SB_KERNMOUNT)
+			return get_tree_nodev(fc, erofs_fc_fill_pseudo_super);
+		if (ctx->opt.fsid)
+			return get_tree_nodev(fc, erofs_fc_fill_super);
+	}
 
 	return get_tree_bdev(fc, erofs_fc_fill_super);
 }
@@ -849,6 +865,8 @@ static void erofs_fc_free(struct fs_context *fc)
 {
 	struct erofs_fs_context *ctx = fc->fs_private;
 
+	if (!ctx)
+		return;
 	erofs_free_dev_context(ctx->devs);
 	kfree(ctx->opt.fsid);
 	kfree(ctx->opt.domain_id);
@@ -864,8 +882,12 @@ static const struct fs_context_operations erofs_context_ops = {
 
 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)
+		goto out;
+
+	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
 	ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
@@ -878,6 +900,7 @@ static int erofs_init_fs_context(struct fs_context *fc)
 	idr_init(&ctx->devs->tree);
 	init_rwsem(&ctx->devs->rwsem);
 	erofs_default_options(ctx);
+out:
 	fc->ops = &erofs_context_ops;
 	return 0;
 }
@@ -892,6 +915,10 @@ 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))
 		generic_shutdown_super(sb);
 	else
@@ -916,8 +943,8 @@ static void erofs_put_super(struct super_block *sb)
 {
 	struct erofs_sb_info *const sbi = EROFS_SB(sb);
 
-	DBG_BUGON(!sbi);
-
+	if (!sbi)
+		return;
 	erofs_unregister_sysfs(sb);
 	erofs_shrinker_unregister(sb);
 #ifdef CONFIG_EROFS_FS_ZIP
@@ -927,7 +954,7 @@ static void erofs_put_super(struct super_block *sb)
 	erofs_fscache_unregister_cookie(&sbi->s_fscache);
 }
 
-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

On 9/2/22 6:53 PM, Jia Zhu wrote:
> A new fscache-based shared domain mode is going to be introduced for
> erofs. In which case, same data blobs in same domain will be shared
> and reused to reduce on-disk space usage.
> 
> As the first step, we use pseudo mnt to manage and maintain domain's
> lifecycle.
> 
> The implementation of sharing blobs will be introduced in subsequent
> patches.
> 
> Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
> ---
>  fs/erofs/fscache.c  | 95 ++++++++++++++++++++++++++++++++++++++++++++-
>  fs/erofs/internal.h | 18 ++++++++-
>  fs/erofs/super.c    | 51 ++++++++++++++++++------
>  3 files changed, 149 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index 8e01d89c3319..439dd3cc096a 100644
> --- a/fs/erofs/fscache.c
> +++ b/fs/erofs/fscache.c
> @@ -1,10 +1,15 @@
>  // SPDX-License-Identifier: GPL-2.0-or-later
>  /*
>   * Copyright (C) 2022, Alibaba Cloud
> + * Copyright (C) 2022, Bytedance Inc. All rights reserved.
>   */
>  #include <linux/fscache.h>
>  #include "internal.h"
>  
> +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)
>  {
> @@ -417,6 +422,87 @@ const struct address_space_operations erofs_fscache_access_aops = {
>  	.readahead = erofs_fscache_readahead,
>  };
>  
> +static void erofs_fscache_domain_get(struct erofs_domain *domain)
> +{
> +	if (!domain)
> +		return;
> +	refcount_inc(&domain->ref);
> +}

It seems that the input @domain can not be NULL, and thus the NULL check
is not needed.

Besides how about:

struct erofs_domain *domain erofs_fscache_domain_get(struct erofs_domain
*domain)
{
	refcount_inc(&domain->ref);
	return domain;
}

> +
> +static void erofs_fscache_domain_put(struct erofs_domain *domain)
> +{
> +	if (!domain)
> +		return;
> +	if (refcount_dec_and_test(&domain->ref)) {
> +		fscache_relinquish_volume(domain->volume, NULL, false);
> +		mutex_lock(&erofs_domain_list_lock);
> +		list_del(&domain->list);
> +		mutex_unlock(&erofs_domain_list_lock);
> +		kfree(domain->domain_id);
> +		kfree(domain);
> +	}
> +}
> +
> +static int erofs_fscache_init_domain(struct super_block *sb)
> +{
> +	int err;
> +	struct erofs_domain *domain;
> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
> +
> +	domain = kzalloc(sizeof(struct erofs_domain), GFP_KERNEL);
> +	if (!domain)
> +		return -ENOMEM;
> +
> +	domain->domain_id = kstrdup(sbi->opt.domain_id, GFP_KERNEL);
> +	if (!domain->domain_id) {
> +		kfree(domain);
> +		return -ENOMEM;
> +	}
> +	sbi->domain = domain;
> +	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;
> +		}
> +	}
> +	err = erofs_fscache_register_fs(sb);
> +	if (err)
> +		goto out;
> +
> +	domain->volume = sbi->volume;
> +	refcount_set(&domain->ref, 1);
> +	mutex_init(&domain->mutex);
> +	list_add(&domain->list, &erofs_domain_list);
> +	return 0;
> +out:
> +	kfree(domain->domain_id);
> +	kfree(domain);
> +	sbi->domain = NULL;
> +	return err;
> +}
> +
> +int erofs_fscache_register_domain(struct super_block *sb)
> +{
> +	int err;
> +	struct erofs_domain *domain;
> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
> +
> +	mutex_lock(&erofs_domain_list_lock);
> +	list_for_each_entry(domain, &erofs_domain_list, list) {
> +		if (!strcmp(domain->domain_id, sbi->opt.domain_id)) {
> +			erofs_fscache_domain_get(domain);
> +			sbi->domain = domain;

			sbi->domain = erofs_fscache_domain_get(domain);
			
> +			sbi->volume = domain->volume;
> +			mutex_unlock(&erofs_domain_list_lock);
> +			return 0;
> +		}
> +	}
> +	err = erofs_fscache_init_domain(sb);
> +	mutex_unlock(&erofs_domain_list_lock);
> +	return err;
> +}
> +
>  int erofs_fscache_register_cookie(struct super_block *sb,
>  				  struct erofs_fscache **fscache,
>  				  char *name, bool need_inode)
> @@ -495,7 +581,8 @@ int erofs_fscache_register_fs(struct super_block *sb)
>  	char *name;
>  	int ret = 0;
>  
> -	name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
> +	name = kasprintf(GFP_KERNEL, "erofs,%s",
> +			sbi->domain ? sbi->domain->domain_id : sbi->opt.fsid);

Do we also need to encode the cookie name in the "<domain_id>,<fsid>"
format? This will affect the path of the cache files.

>  	if (!name)
>  		return -ENOMEM;
>  
> @@ -515,6 +602,10 @@ void erofs_fscache_unregister_fs(struct super_block *sb)
>  {
>  	struct erofs_sb_info *sbi = EROFS_SB(sb);
>  
> -	fscache_relinquish_volume(sbi->volume, NULL, false);
> +	if (sbi->domain)
> +		erofs_fscache_domain_put(sbi->domain);
> +	else
> +		fscache_relinquish_volume(sbi->volume, NULL, false);
>  	sbi->volume = NULL;
> +	sbi->domain = NULL;
>  }
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index fe435d077f1a..2790c93ffb83 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -99,6 +99,14 @@ struct erofs_sb_lz4_info {
>  	u16 max_pclusterblks;
>  };
>  
> +struct erofs_domain {
> +	refcount_t ref;
> +	struct mutex mutex;
> +	struct list_head list;
> +	struct fscache_volume *volume;
> +	char *domain_id;
> +};
> +
>  struct erofs_fscache {
>  	struct fscache_cookie *cookie;
>  	struct inode *inode;
> @@ -158,6 +166,7 @@ struct erofs_sb_info {
>  	/* fscache support */
>  	struct fscache_volume *volume;
>  	struct erofs_fscache *s_fscache;
> +	struct erofs_domain *domain;
>  };
>  
>  #define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info)
> @@ -394,6 +403,7 @@ 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;
> @@ -610,6 +620,7 @@ static inline int z_erofs_load_lzma_config(struct super_block *sb,
>  #ifdef CONFIG_EROFS_FS_ONDEMAND
>  int erofs_fscache_register_fs(struct super_block *sb);
>  void erofs_fscache_unregister_fs(struct super_block *sb);
> +int erofs_fscache_register_domain(struct super_block *sb);
>  
>  int erofs_fscache_register_cookie(struct super_block *sb,
>  				  struct erofs_fscache **fscache,
> @@ -620,10 +631,15 @@ extern const struct address_space_operations erofs_fscache_access_aops;
>  #else
>  static inline int erofs_fscache_register_fs(struct super_block *sb)
>  {
> -	return 0;
> +	return -EOPNOTSUPP;
>  }
>  static inline void erofs_fscache_unregister_fs(struct super_block *sb) {}
>  
> +static inline int erofs_fscache_register_domain(const struct super_block *sb)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  static inline int erofs_fscache_register_cookie(struct super_block *sb,
>  						struct erofs_fscache **fscache,
>  						char *name, bool need_inode)
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index d01109069c6b..69de1731f454 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -688,6 +688,13 @@ 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;
> @@ -715,12 +722,17 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  		sb->s_blocksize = EROFS_BLKSIZ;
>  		sb->s_blocksize_bits = LOG_BLOCK_SIZE;
>  
> -		err = erofs_fscache_register_fs(sb);
> -		if (err)
> -			return err;
> -
> -		err = erofs_fscache_register_cookie(sb, &sbi->s_fscache,
> -						    sbi->opt.fsid, true);
> +		if (sbi->opt.domain_id) {
> +			err = erofs_fscache_register_domain(sb);
> +			if (err)
> +				return err;
> +		} else {
> +			err = erofs_fscache_register_fs(sb);
> +			if (err)
> +				return err;
> +			err = erofs_fscache_register_cookie(sb, &sbi->s_fscache,
> +					sbi->opt.fsid, true);

We'd better keep only one entry to the fscache related codes. How about
moving erofs_fscache_register_cookie(), i.e. registering cookie for
bootstrap, into erofs_fscache_register_fs()? Similarly, check the
domain_id and call erofs_fscache_register_domain() inside
erofs_fscache_register_fs().

Similarly, check domain_id and call erofs_domain_register_cookie()
inside erofs_fscache_register_cookie().



> +		}
>  		if (err)
>  			return err;
>  
> @@ -798,8 +810,12 @@ static int erofs_fc_get_tree(struct fs_context *fc)
>  {
>  	struct erofs_fs_context *ctx = fc->fs_private;
>  
> -	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->opt.fsid)
> -		return get_tree_nodev(fc, erofs_fc_fill_super);
> +	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND)) {
> +		if (!ctx && fc->sb_flags & SB_KERNMOUNT)
> +			return get_tree_nodev(fc, erofs_fc_fill_pseudo_super);
> +		if (ctx->opt.fsid)
> +			return get_tree_nodev(fc, erofs_fc_fill_super);
> +	}
>  
>  	return get_tree_bdev(fc, erofs_fc_fill_super);
>  }
> @@ -849,6 +865,8 @@ static void erofs_fc_free(struct fs_context *fc)
>  {
>  	struct erofs_fs_context *ctx = fc->fs_private;
>  
> +	if (!ctx)
> +		return;
>  	erofs_free_dev_context(ctx->devs);
>  	kfree(ctx->opt.fsid);
>  	kfree(ctx->opt.domain_id);
> @@ -864,8 +882,12 @@ static const struct fs_context_operations erofs_context_ops = {
>  
>  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)
> +		goto out;
> +
> +	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>  	if (!ctx)
>  		return -ENOMEM;
>  	ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
> @@ -878,6 +900,7 @@ static int erofs_init_fs_context(struct fs_context *fc)
>  	idr_init(&ctx->devs->tree);
>  	init_rwsem(&ctx->devs->rwsem);
>  	erofs_default_options(ctx);
> +out:
>  	fc->ops = &erofs_context_ops;
>  	return 0;
>  }
> @@ -892,6 +915,10 @@ 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))
>  		generic_shutdown_super(sb);
>  	else
> @@ -916,8 +943,8 @@ static void erofs_put_super(struct super_block *sb)
>  {
>  	struct erofs_sb_info *const sbi = EROFS_SB(sb);
>  
> -	DBG_BUGON(!sbi);
> -
> +	if (!sbi)
> +		return;
>  	erofs_unregister_sysfs(sb);
>  	erofs_shrinker_unregister(sb);
>  #ifdef CONFIG_EROFS_FS_ZIP
> @@ -927,7 +954,7 @@ static void erofs_put_super(struct super_block *sb)
>  	erofs_fscache_unregister_cookie(&sbi->s_fscache);
>  }
>  
> -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,

-- 
Thanks,
Jingbo

在 2022/9/9 16:42, JeffleXu 写道:
> 
> 
> On 9/2/22 6:53 PM, Jia Zhu wrote:
>> A new fscache-based shared domain mode is going to be introduced for
>> erofs. In which case, same data blobs in same domain will be shared
>> and reused to reduce on-disk space usage.
>>
>> As the first step, we use pseudo mnt to manage and maintain domain's
>> lifecycle.
>>
>> The implementation of sharing blobs will be introduced in subsequent
>> patches.
>>
>> Signed-off-by: Jia Zhu <zhujia.zj@bytedance.com>
>> ---
>>   fs/erofs/fscache.c  | 95 ++++++++++++++++++++++++++++++++++++++++++++-
>>   fs/erofs/internal.h | 18 ++++++++-
>>   fs/erofs/super.c    | 51 ++++++++++++++++++------
>>   3 files changed, 149 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
>> index 8e01d89c3319..439dd3cc096a 100644
>> --- a/fs/erofs/fscache.c
>> +++ b/fs/erofs/fscache.c
>> @@ -1,10 +1,15 @@
>>   // SPDX-License-Identifier: GPL-2.0-or-later
>>   /*
>>    * Copyright (C) 2022, Alibaba Cloud
>> + * Copyright (C) 2022, Bytedance Inc. All rights reserved.
>>    */
>>   #include <linux/fscache.h>
>>   #include "internal.h"
>>   
>> +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)
>>   {
>> @@ -417,6 +422,87 @@ const struct address_space_operations erofs_fscache_access_aops = {
>>   	.readahead = erofs_fscache_readahead,
>>   };
>>   
>> +static void erofs_fscache_domain_get(struct erofs_domain *domain)
>> +{
>> +	if (!domain)
>> +		return;
>> +	refcount_inc(&domain->ref);
>> +}
> 
Hi Jingbo,
Thanks for your careful review.
> It seems that the input @domain can not be NULL, and thus the NULL check
> is not needed.
> 
I will remove it in next version.
> Besides how about:
> 
> struct erofs_domain *domain erofs_fscache_domain_get(struct erofs_domain
> *domain)
> {
> 	refcount_inc(&domain->ref);
> 	return domain;
> }
> 
Thanks for the suggestion, I will apply it.
>> +
>> +static void erofs_fscache_domain_put(struct erofs_domain *domain)
>> +{
>> +	if (!domain)
>> +		return;
>> +	if (refcount_dec_and_test(&domain->ref)) {
>> +		fscache_relinquish_volume(domain->volume, NULL, false);
>> +		mutex_lock(&erofs_domain_list_lock);
>> +		list_del(&domain->list);
>> +		mutex_unlock(&erofs_domain_list_lock);
>> +		kfree(domain->domain_id);
>> +		kfree(domain);
>> +	}
>> +}
>> +
>> +static int erofs_fscache_init_domain(struct super_block *sb)
>> +{
>> +	int err;
>> +	struct erofs_domain *domain;
>> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
>> +
>> +	domain = kzalloc(sizeof(struct erofs_domain), GFP_KERNEL);
>> +	if (!domain)
>> +		return -ENOMEM;
>> +
>> +	domain->domain_id = kstrdup(sbi->opt.domain_id, GFP_KERNEL);
>> +	if (!domain->domain_id) {
>> +		kfree(domain);
>> +		return -ENOMEM;
>> +	}
>> +	sbi->domain = domain;
>> +	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;
>> +		}
>> +	}
>> +	err = erofs_fscache_register_fs(sb);
>> +	if (err)
>> +		goto out;
>> +
>> +	domain->volume = sbi->volume;
>> +	refcount_set(&domain->ref, 1);
>> +	mutex_init(&domain->mutex);
>> +	list_add(&domain->list, &erofs_domain_list);
>> +	return 0;
>> +out:
>> +	kfree(domain->domain_id);
>> +	kfree(domain);
>> +	sbi->domain = NULL;
>> +	return err;
>> +}
>> +
>> +int erofs_fscache_register_domain(struct super_block *sb)
>> +{
>> +	int err;
>> +	struct erofs_domain *domain;
>> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
>> +
>> +	mutex_lock(&erofs_domain_list_lock);
>> +	list_for_each_entry(domain, &erofs_domain_list, list) {
>> +		if (!strcmp(domain->domain_id, sbi->opt.domain_id)) {
>> +			erofs_fscache_domain_get(domain);
>> +			sbi->domain = domain;
> 
> 			sbi->domain = erofs_fscache_domain_get(domain);
> 			
>> +			sbi->volume = domain->volume;
>> +			mutex_unlock(&erofs_domain_list_lock);
>> +			return 0;
>> +		}
>> +	}
>> +	err = erofs_fscache_init_domain(sb);
>> +	mutex_unlock(&erofs_domain_list_lock);
>> +	return err;
>> +}
>> +
>>   int erofs_fscache_register_cookie(struct super_block *sb,
>>   				  struct erofs_fscache **fscache,
>>   				  char *name, bool need_inode)
>> @@ -495,7 +581,8 @@ int erofs_fscache_register_fs(struct super_block *sb)
>>   	char *name;
>>   	int ret = 0;
>>   
>> -	name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
>> +	name = kasprintf(GFP_KERNEL, "erofs,%s",
>> +			sbi->domain ? sbi->domain->domain_id : sbi->opt.fsid);
> 
> Do we also need to encode the cookie name in the "<domain_id>,<fsid>"
> format? This will affect the path of the cache files.
> 
I think even though the cookies have the same name, they belong to
different volumes(path). Cookies do not affect each other.
Are there other benefits to doing so?
>>   	if (!name)
>>   		return -ENOMEM;
>>   
>> @@ -515,6 +602,10 @@ void erofs_fscache_unregister_fs(struct super_block *sb)
>>   {
>>   	struct erofs_sb_info *sbi = EROFS_SB(sb);
>>   
>> -	fscache_relinquish_volume(sbi->volume, NULL, false);
>> +	if (sbi->domain)
>> +		erofs_fscache_domain_put(sbi->domain);
>> +	else
>> +		fscache_relinquish_volume(sbi->volume, NULL, false);
>>   	sbi->volume = NULL;
>> +	sbi->domain = NULL;
>>   }
>> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
>> index fe435d077f1a..2790c93ffb83 100644
>> --- a/fs/erofs/internal.h
>> +++ b/fs/erofs/internal.h
>> @@ -99,6 +99,14 @@ struct erofs_sb_lz4_info {
>>   	u16 max_pclusterblks;
>>   };
>>   
>> +struct erofs_domain {
>> +	refcount_t ref;
>> +	struct mutex mutex;
>> +	struct list_head list;
>> +	struct fscache_volume *volume;
>> +	char *domain_id;
>> +};
>> +
>>   struct erofs_fscache {
>>   	struct fscache_cookie *cookie;
>>   	struct inode *inode;
>> @@ -158,6 +166,7 @@ struct erofs_sb_info {
>>   	/* fscache support */
>>   	struct fscache_volume *volume;
>>   	struct erofs_fscache *s_fscache;
>> +	struct erofs_domain *domain;
>>   };
>>   
>>   #define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info)
>> @@ -394,6 +403,7 @@ 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;
>> @@ -610,6 +620,7 @@ static inline int z_erofs_load_lzma_config(struct super_block *sb,
>>   #ifdef CONFIG_EROFS_FS_ONDEMAND
>>   int erofs_fscache_register_fs(struct super_block *sb);
>>   void erofs_fscache_unregister_fs(struct super_block *sb);
>> +int erofs_fscache_register_domain(struct super_block *sb);
>>   
>>   int erofs_fscache_register_cookie(struct super_block *sb,
>>   				  struct erofs_fscache **fscache,
>> @@ -620,10 +631,15 @@ extern const struct address_space_operations erofs_fscache_access_aops;
>>   #else
>>   static inline int erofs_fscache_register_fs(struct super_block *sb)
>>   {
>> -	return 0;
>> +	return -EOPNOTSUPP;
>>   }
>>   static inline void erofs_fscache_unregister_fs(struct super_block *sb) {}
>>   
>> +static inline int erofs_fscache_register_domain(const struct super_block *sb)
>> +{
>> +	return -EOPNOTSUPP;
>> +}
>> +
>>   static inline int erofs_fscache_register_cookie(struct super_block *sb,
>>   						struct erofs_fscache **fscache,
>>   						char *name, bool need_inode)
>> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
>> index d01109069c6b..69de1731f454 100644
>> --- a/fs/erofs/super.c
>> +++ b/fs/erofs/super.c
>> @@ -688,6 +688,13 @@ 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;
>> @@ -715,12 +722,17 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>>   		sb->s_blocksize = EROFS_BLKSIZ;
>>   		sb->s_blocksize_bits = LOG_BLOCK_SIZE;
>>   
>> -		err = erofs_fscache_register_fs(sb);
>> -		if (err)
>> -			return err;
>> -
>> -		err = erofs_fscache_register_cookie(sb, &sbi->s_fscache,
>> -						    sbi->opt.fsid, true);
>> +		if (sbi->opt.domain_id) {
>> +			err = erofs_fscache_register_domain(sb);
>> +			if (err)
>> +				return err;
>> +		} else {
>> +			err = erofs_fscache_register_fs(sb);
>> +			if (err)
>> +				return err;
>> +			err = erofs_fscache_register_cookie(sb, &sbi->s_fscache,
>> +					sbi->opt.fsid, true);
> 
> We'd better keep only one entry to the fscache related codes. How about
> moving erofs_fscache_register_cookie(), i.e. registering cookie for
> bootstrap, into erofs_fscache_register_fs()? Similarly, check the
> domain_id and call erofs_fscache_register_domain() inside
> erofs_fscache_register_fs().
> 
> Similarly, check domain_id and call erofs_domain_register_cookie()
> inside erofs_fscache_register_cookie().
> 
Thanks, that looks great, I will revise it in next version.
> 
> 
>> +		}
>>   		if (err)
>>   			return err;
>>   
>> @@ -798,8 +810,12 @@ static int erofs_fc_get_tree(struct fs_context *fc)
>>   {
>>   	struct erofs_fs_context *ctx = fc->fs_private;
>>   
>> -	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && ctx->opt.fsid)
>> -		return get_tree_nodev(fc, erofs_fc_fill_super);
>> +	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND)) {
>> +		if (!ctx && fc->sb_flags & SB_KERNMOUNT)
>> +			return get_tree_nodev(fc, erofs_fc_fill_pseudo_super);
>> +		if (ctx->opt.fsid)
>> +			return get_tree_nodev(fc, erofs_fc_fill_super);
>> +	}
>>   
>>   	return get_tree_bdev(fc, erofs_fc_fill_super);
>>   }
>> @@ -849,6 +865,8 @@ static void erofs_fc_free(struct fs_context *fc)
>>   {
>>   	struct erofs_fs_context *ctx = fc->fs_private;
>>   
>> +	if (!ctx)
>> +		return;
>>   	erofs_free_dev_context(ctx->devs);
>>   	kfree(ctx->opt.fsid);
>>   	kfree(ctx->opt.domain_id);
>> @@ -864,8 +882,12 @@ static const struct fs_context_operations erofs_context_ops = {
>>   
>>   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)
>> +		goto out;
>> +
>> +	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
>>   	if (!ctx)
>>   		return -ENOMEM;
>>   	ctx->devs = kzalloc(sizeof(struct erofs_dev_context), GFP_KERNEL);
>> @@ -878,6 +900,7 @@ static int erofs_init_fs_context(struct fs_context *fc)
>>   	idr_init(&ctx->devs->tree);
>>   	init_rwsem(&ctx->devs->rwsem);
>>   	erofs_default_options(ctx);
>> +out:
>>   	fc->ops = &erofs_context_ops;
>>   	return 0;
>>   }
>> @@ -892,6 +915,10 @@ 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))
>>   		generic_shutdown_super(sb);
>>   	else
>> @@ -916,8 +943,8 @@ static void erofs_put_super(struct super_block *sb)
>>   {
>>   	struct erofs_sb_info *const sbi = EROFS_SB(sb);
>>   
>> -	DBG_BUGON(!sbi);
>> -
>> +	if (!sbi)
>> +		return;
>>   	erofs_unregister_sysfs(sb);
>>   	erofs_shrinker_unregister(sb);
>>   #ifdef CONFIG_EROFS_FS_ZIP
>> @@ -927,7 +954,7 @@ static void erofs_put_super(struct super_block *sb)
>>   	erofs_fscache_unregister_cookie(&sbi->s_fscache);
>>   }
>>   
>> -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,
> 

On 9/13/22 12:31 PM, Jia Zhu wrote:
> 
> 
> 在 2022/9/9 16:42, JeffleXu 写道:
>>>   int erofs_fscache_register_cookie(struct super_block *sb,
>>>                     struct erofs_fscache **fscache,
>>>                     char *name, bool need_inode)
>>> @@ -495,7 +581,8 @@ int erofs_fscache_register_fs(struct super_block
>>> *sb)
>>>       char *name;
>>>       int ret = 0;
>>>   -    name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
>>> +    name = kasprintf(GFP_KERNEL, "erofs,%s",
>>> +            sbi->domain ? sbi->domain->domain_id : sbi->opt.fsid);
>>
>> Do we also need to encode the cookie name in the "<domain_id>,<fsid>"
>> format? This will affect the path of the cache files.
>>
> I think even though the cookies have the same name, they belong to
> different volumes(path). Cookies do not affect each other.
> Are there other benefits to doing so?

Okay. The current implementation is correct. Please ignore the noise.


-- 
Thanks,
Jingbo

On 9/2/22 6:53 PM, Jia Zhu wrote:

>  int erofs_fscache_register_cookie(struct super_block *sb,
>  				  struct erofs_fscache **fscache,
>  				  char *name, bool need_inode)
> @@ -495,7 +581,8 @@ int erofs_fscache_register_fs(struct super_block *sb)
>  	char *name;
>  	int ret = 0;
>  
> -	name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
> +	name = kasprintf(GFP_KERNEL, "erofs,%s",
> +			sbi->domain ? sbi->domain->domain_id : sbi->opt.fsid);
>  	if (!name)
>  		return -ENOMEM;
>  

What if domain_id and fsid has the same value?

How about the format "erofs,<domain_id>,<fsid>"? While in the
non-share-domain mode, is the format like "erofs,,<fsid>" or the default
"erofs,<fsid>"?


-- 
Thanks,
Jingbo

在 2022/9/14 11:02, JeffleXu 写道:
> 
> 
> On 9/2/22 6:53 PM, Jia Zhu wrote:
> 
>>   int erofs_fscache_register_cookie(struct super_block *sb,
>>   				  struct erofs_fscache **fscache,
>>   				  char *name, bool need_inode)
>> @@ -495,7 +581,8 @@ int erofs_fscache_register_fs(struct super_block *sb)
>>   	char *name;
>>   	int ret = 0;
>>   
>> -	name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
>> +	name = kasprintf(GFP_KERNEL, "erofs,%s",
>> +			sbi->domain ? sbi->domain->domain_id : sbi->opt.fsid);
>>   	if (!name)
>>   		return -ENOMEM;
>>   
> 
> What if domain_id and fsid has the same value?
> 
> How about the format "erofs,<domain_id>,<fsid>"? While in the
> non-share-domain mode, is the format like "erofs,,<fsid>" or the default
> "erofs,<fsid>"?
> 
Thanks for pointing this out. I'll revise it.
>