Re: [PATCH v8 10/20] erofs: register fscache volume

[Gao Xiang]

On Wed, Apr 06, 2022 at 03:56:02PM +0800, Jeffle Xu wrote:
> A new fscache based mode is going to be introduced for erofs, in which
> case on-demand read semantics is implemented through fscache.
> 
> As the first step, register fscache volume for each erofs filesystem.
> That means, data blobs can not be shared among erofs filesystems. In the
> following iteration, we are going to introduce the domain semantics, in
> which case several erofs filesystems can belong to one domain, and data
> blobs can be shared among these erofs filesystems of one domain.
> 
> Signed-off-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

Thanks,
Gao Xiang

> ---
>  fs/erofs/Kconfig    | 10 ++++++++++
>  fs/erofs/Makefile   |  1 +
>  fs/erofs/fscache.c  | 37 +++++++++++++++++++++++++++++++++++++
>  fs/erofs/internal.h | 13 +++++++++++++
>  fs/erofs/super.c    |  7 +++++++
>  5 files changed, 68 insertions(+)
>  create mode 100644 fs/erofs/fscache.c
> 
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index f57255ab88ed..3d05265e3e8e 100644
> --- a/fs/erofs/Kconfig
> +++ b/fs/erofs/Kconfig
> @@ -98,3 +98,13 @@ config EROFS_FS_ZIP_LZMA
>  	  systems will be readable without selecting this option.
>  
>  	  If unsure, say N.
> +
> +config EROFS_FS_ONDEMAND
> +	bool "EROFS fscache-based ondemand-read"
> +	depends on CACHEFILES_ONDEMAND && (EROFS_FS=m && FSCACHE || EROFS_FS=y && FSCACHE=y)
> +	default n
> +	help
> +	  EROFS is mounted from data blobs and on-demand read semantics is
> +	  implemented through fscache.
> +
> +	  If unsure, say N.
> diff --git a/fs/erofs/Makefile b/fs/erofs/Makefile
> index 8a3317e38e5a..99bbc597a3e9 100644
> --- a/fs/erofs/Makefile
> +++ b/fs/erofs/Makefile
> @@ -5,3 +5,4 @@ erofs-objs := super.o inode.o data.o namei.o dir.o utils.o pcpubuf.o sysfs.o
>  erofs-$(CONFIG_EROFS_FS_XATTR) += xattr.o
>  erofs-$(CONFIG_EROFS_FS_ZIP) += decompressor.o zmap.o zdata.o
>  erofs-$(CONFIG_EROFS_FS_ZIP_LZMA) += decompressor_lzma.o
> +erofs-$(CONFIG_EROFS_FS_ONDEMAND) += fscache.o
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> new file mode 100644
> index 000000000000..7a6d0239ebb1
> --- /dev/null
> +++ b/fs/erofs/fscache.c
> @@ -0,0 +1,37 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2022, Alibaba Cloud
> + */
> +#include <linux/fscache.h>
> +#include "internal.h"
> +
> +int erofs_fscache_register_fs(struct super_block *sb)
> +{
> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
> +	struct fscache_volume *volume;
> +	char *name;
> +	int ret = 0;
> +
> +	name = kasprintf(GFP_KERNEL, "erofs,%s", sbi->opt.fsid);
> +	if (!name)
> +		return -ENOMEM;
> +
> +	volume = fscache_acquire_volume(name, NULL, NULL, 0);
> +	if (IS_ERR_OR_NULL(volume)) {
> +		erofs_err(sb, "failed to register volume for %s", name);
> +		ret = volume ? PTR_ERR(volume) : -EOPNOTSUPP;
> +		volume = NULL;
> +	}
> +
> +	sbi->volume = volume;
> +	kfree(name);
> +	return ret;
> +}
> +
> +void erofs_fscache_unregister_fs(struct super_block *sb)
> +{
> +	struct erofs_sb_info *sbi = EROFS_SB(sb);
> +
> +	fscache_relinquish_volume(sbi->volume, NULL, false);
> +	sbi->volume = NULL;
> +}
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 05a97533b1e9..952a2f483f94 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -74,6 +74,7 @@ struct erofs_mount_opts {
>  	unsigned int max_sync_decompress_pages;
>  #endif
>  	unsigned int mount_opt;
> +	char *fsid;
>  };
>  
>  struct erofs_dev_context {
> @@ -146,6 +147,9 @@ struct erofs_sb_info {
>  	/* sysfs support */
>  	struct kobject s_kobj;		/* /sys/fs/erofs/<devname> */
>  	struct completion s_kobj_unregister;
> +
> +	/* fscache support */
> +	struct fscache_volume *volume;
>  };
>  
>  #define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info)
> @@ -618,6 +622,15 @@ static inline int z_erofs_load_lzma_config(struct super_block *sb,
>  }
>  #endif	/* !CONFIG_EROFS_FS_ZIP */
>  
> +/* fscache.c */
> +#ifdef CONFIG_EROFS_FS_ONDEMAND
> +int erofs_fscache_register_fs(struct super_block *sb);
> +void erofs_fscache_unregister_fs(struct super_block *sb);
> +#else
> +static inline int erofs_fscache_register_fs(struct super_block *sb) { return 0; }
> +static inline void erofs_fscache_unregister_fs(struct super_block *sb) {}
> +#endif
> +
>  #define EFSCORRUPTED    EUCLEAN         /* Filesystem is corrupted */
>  
>  #endif	/* __EROFS_INTERNAL_H */
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index 0c4b41130c2f..6590ed1b7d3b 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -601,6 +601,12 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  	sbi->devs = ctx->devs;
>  	ctx->devs = NULL;
>  
> +	if (erofs_is_fscache_mode(sb)) {
> +		err = erofs_fscache_register_fs(sb);
> +		if (err)
> +			return err;
> +	}
> +
>  	err = erofs_read_superblock(sb);
>  	if (err)
>  		return err;
> @@ -757,6 +763,7 @@ static void erofs_kill_sb(struct super_block *sb)
>  
>  	erofs_free_dev_context(sbi->devs);
>  	fs_put_dax(sbi->dax_dev);
> +	erofs_fscache_unregister_fs(sb);
>  	kfree(sbi);
>  	sb->s_fs_info = NULL;
>  }
> -- 
> 2.27.0