[External] Re: [PATCH V2 5/5] erofs: support fscache based shared domain

[Jia Zhu]

在 2022/9/13 14:27, JeffleXu 写道:
> 
> 
> On 9/2/22 6:53 PM, Jia Zhu wrote:
>> 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/fscache.c  | 73 +++++++++++++++++++++++++++++++++++++++++++++
>>   fs/erofs/internal.h | 12 ++++++++
>>   fs/erofs/super.c    | 10 +++++--
>>   3 files changed, 93 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
>> index 439dd3cc096a..c01845808ede 100644
>> --- a/fs/erofs/fscache.c
>> +++ b/fs/erofs/fscache.c
>> @@ -559,12 +559,27 @@ int erofs_fscache_register_cookie(struct super_block *sb,
>>   void erofs_fscache_unregister_cookie(struct erofs_fscache **fscache)
>>   {
>>   	struct erofs_fscache *ctx = *fscache;
>> +	struct erofs_domain *domain;
>>   
>>   	if (!ctx)
>>   		return;
>> +	domain = ctx->domain;
>> +	if (domain) {
>> +		mutex_lock(&domain->mutex);
>> +		/* Cookie is still in use */
>> +		if (atomic_read(&ctx->anon_inode->i_count) > 1) {
>> +			iput(ctx->anon_inode);
>> +			mutex_unlock(&domain->mutex);
>> +			return;
>> +		}
>> +		iput(ctx->anon_inode);
>> +		kfree(ctx->name);
>> +		mutex_unlock(&domain->mutex);
>> +	}
>>   
>>   	fscache_unuse_cookie(ctx->cookie, NULL, NULL);
>>   	fscache_relinquish_cookie(ctx->cookie, false);
>> +	erofs_fscache_domain_put(domain);
>>   	ctx->cookie = NULL;
>>   
>>   	iput(ctx->inode);
>> @@ -609,3 +624,61 @@ void erofs_fscache_unregister_fs(struct super_block *sb)
>>   	sbi->volume = NULL;
>>   	sbi->domain = NULL;
>>   }
>> +
>> +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;
> 
> Shall we clean up the above registered cookie in the error path?
> 
If this step fails, error will be transmitted to vfs_get_tree() and
erofs_kill_sb() will relinquish the cookie.
>> +
>> +	inode = new_inode(erofs_pseudo_mnt->mnt_sb);
>> +	if (!inode) {
>> +		kfree(ctx->name);
>> +		return -ENOMEM;
>> +	}
> 
> Ditto.
> 
>> +
>> +	ctx->domain = domain;
>> +	ctx->anon_inode = inode;
>> +	inode->i_private = ctx;
>> +	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 = erofs_pseudo_mnt->mnt_sb;
>> +
>> +	mutex_lock(&domain->mutex);
> 
> What is domain->mutex used for?
> 
This lock is used to avoid race conditions between cookie's
traverse/del/insert in the inode list.
It seems to be possible to increase the granularity of the lock
after v2's change "Only initialize one pseudo fs to manage anonymous 
inodes(cookies).".
> 
>> +	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;
>> +			igrab(inode);
>> +			mutex_unlock(&domain->mutex);
>> +			return 0;
>> +		}
>> +	}
>> +	err = erofs_fscache_domain_init_cookie(sb, fscache, name, need_inode);
>> +	mutex_unlock(&domain->mutex);
>> +	return err;
>> +}
>> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
>> index 2790c93ffb83..efa4f4ad77cc 100644
>> --- a/fs/erofs/internal.h
>> +++ b/fs/erofs/internal.h
>> @@ -110,6 +110,9 @@ struct erofs_domain {
>>   struct erofs_fscache {
>>   	struct fscache_cookie *cookie;
>>   	struct inode *inode;
>> +	struct inode *anon_inode;
> 
> Why can't we reuse @inode for anon_inode?
> 
We use pseudo sb's anonymous inodes list to manage the cookie.
Wouldn't it be a bit of messy if reuses erofs meta inode?
> 
>> +	struct erofs_domain *domain;
>> +	char *name;
>>   };
>>   
>>   struct erofs_sb_info {
>> @@ -625,6 +628,9 @@ 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;
>> @@ -646,6 +652,12 @@ 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 667a78f0ee70..11c5ba84567c 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 {
>> @@ -726,6 +730,8 @@ 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)
>