Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

[Gao Xiang]

Hi Sasha,

I'm not sure why we need to backport this into stable kernels, as there
are users who use EROFS over fscache on these stable kernels.

The functionality works and it's a breaking change.  Could you please
kindly tell why?

Thanks,
Gao Xiang

On Mon, Oct 12, 2026 at 10:00:42PM -0400, Sasha Levin wrote:
> This is a note to let you know that I've just added the patch titled
> 
>     erofs: remove fscache backend entirely
> 
> to the 6.18-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      erofs-remove-fscache-backend-entirely.patch
> and it can be found in the queue-6.18 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.
> 
> 
> 
> commit abe569fd895a5260615eb4e7092f110543705bb7
> Author: Gao Xiang <xiang@kernel.org>
> Date:   Mon Jun 22 09:36:22 2026 +0800
> 
>     erofs: remove fscache backend entirely
>     
>     [ Upstream commit c37460cd9b2fcb61ec66b7eb4fde737e65ec2a56 ]
>     
>     EROFS over fscache was introduced to provide image lazy pulling
>     functionality. After the feature landed, the fscache subsystem made
>     netfs a new hard dependency, which is unexpected for a local filesystem
>     and has an kernel-defined caching hierarchy which could be inflexible
>     compared to the fanotify pre-content hooks. Therefore, this feature has
>     been deprecated for almost two years.
>     
>     As EROFS file-backed mounts and fanotify pre-content hooks both upstream
>     for a while and already providing equivalent functionality (erofs-utils
>     has supported fanotify pre-content hooks), let's remove the fscache
>     backend now.
>     
>     The main application of this feature is Nydus [1], and they plan to move
>     to use fanotify pre-content hooks in the near future too.
>     
>     I hope this patch can be merged into Linux 7.2, which is also motivated
>     by newly found implementation issues [2][3] that are not worth
>     investigating given the deprecation and limited development resources.
>     The associated fscache/cachefiles cleanup patch will follow separately
>     through the vfs tree (netfs) later: it seems fine since the codebase is
>     isolated by CONFIG_CACHEFILES_ONDEMAND.
>     
>     [1] https://github.com/dragonflyoss/nydus/blob/v2.1.0/docs/nydus-fscache.md
>     [2] https://github.com/dragonflyoss/nydus/pull/1824
>     [3] https://lore.kernel.org/r/20260619135800.1594811-1-michael.bommarito@gmail.com
>     
>     Acked-by: Jingbo Xu <jefflexu@linux.alibaba.com>
>     Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
>     Signed-off-by: Sasha Levin <sashal@kernel.org>
> 
> diff --git a/Documentation/filesystems/erofs.rst b/Documentation/filesystems/erofs.rst
> index 08194f194b942..8c96104e91df5 100644
> --- a/Documentation/filesystems/erofs.rst
> +++ b/Documentation/filesystems/erofs.rst
> @@ -125,9 +125,6 @@ dax={always,never}     Use direct access (no page cache).  See
>                         Documentation/filesystems/dax.rst.
>  dax                    A legacy option which is an alias for ``dax=always``.
>  device=%s              Specify a path to an extra device to be used together.
> -fsid=%s                Specify a filesystem image ID for Fscache back-end.
> -domain_id=%s           Specify a domain ID in fscache mode so that different images
> -                       with the same blobs under a given domain ID can share storage.
>  fsoffset=%llu          Specify block-aligned filesystem offset for the primary device.
>  ===================    =========================================================
>  
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index 473a22167c154..3e08d7b174678 100644
> --- a/fs/erofs/Kconfig
> +++ b/fs/erofs/Kconfig
> @@ -3,13 +3,11 @@
>  config EROFS_FS
>  	tristate "EROFS filesystem support"
>  	depends on BLOCK
> -	select CACHEFILES if EROFS_FS_ONDEMAND
>  	select CRC32
>  	select CRYPTO if EROFS_FS_ZIP_ACCEL
>  	select CRYPTO_DEFLATE if EROFS_FS_ZIP_ACCEL
>  	select FS_IOMAP
>  	select LZ4_DECOMPRESS if EROFS_FS_ZIP
> -	select NETFS_SUPPORT if EROFS_FS_ONDEMAND
>  	select XXHASH if EROFS_FS_XATTR
>  	select XZ_DEC if EROFS_FS_ZIP_LZMA
>  	select XZ_DEC_MICROLZMA if EROFS_FS_ZIP_LZMA
> @@ -95,9 +93,6 @@ config EROFS_FS_BACKED_BY_FILE
>  	  be used to simplify error-prone lifetime management of unnecessary
>  	  virtual block devices.
>  
> -	  Note that this feature, along with ongoing fanotify pre-content
> -	  hooks, will eventually replace "EROFS over fscache."
> -
>  	  If you don't want to enable this feature, say N.
>  
>  config EROFS_FS_ZIP
> @@ -179,20 +174,6 @@ config EROFS_FS_ZIP_ACCEL
>  
>  	  If unsure, say N.
>  
> -config EROFS_FS_ONDEMAND
> -	bool "EROFS fscache-based on-demand read support (deprecated)"
> -	depends on EROFS_FS
> -	select FSCACHE
> -	select CACHEFILES_ONDEMAND
> -	help
> -	  This permits EROFS to use fscache-backed data blobs with on-demand
> -	  read support.
> -
> -	  It is now deprecated and scheduled to be removed from the kernel
> -	  after fanotify pre-content hooks are landed.
> -
> -	  If unsure, say N.
> -
>  config EROFS_FS_PCPU_KTHREAD
>  	bool "EROFS per-cpu decompression kthread workers"
>  	depends on EROFS_FS_ZIP
> diff --git a/fs/erofs/Makefile b/fs/erofs/Makefile
> index 549abc4247632..a980f760a673e 100644
> --- a/fs/erofs/Makefile
> +++ b/fs/erofs/Makefile
> @@ -9,4 +9,3 @@ erofs-$(CONFIG_EROFS_FS_ZIP_DEFLATE) += decompressor_deflate.o
>  erofs-$(CONFIG_EROFS_FS_ZIP_ZSTD) += decompressor_zstd.o
>  erofs-$(CONFIG_EROFS_FS_ZIP_ACCEL) += decompressor_crypto.o
>  erofs-$(CONFIG_EROFS_FS_BACKED_BY_FILE) += fileio.o
> -erofs-$(CONFIG_EROFS_FS_ONDEMAND) += fscache.o
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index 3e6b512efe21c..0574384eca18c 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -65,9 +65,7 @@ int erofs_init_metabuf(struct erofs_buf *buf, struct super_block *sb,
>  	if (erofs_is_fileio_mode(sbi)) {
>  		buf->file = sbi->dif0.file;	/* some fs like FUSE needs it */
>  		buf->mapping = buf->file->f_mapping;
> -	} else if (erofs_is_fscache_mode(sb))
> -		buf->mapping = sbi->dif0.fscache->inode->i_mapping;
> -	else
> +	} else
>  		buf->mapping = sb->s_bdev->bd_mapping;
>  	return 0;
>  }
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> deleted file mode 100644
> index 754f7d04488da..0000000000000
> --- a/fs/erofs/fscache.c
> +++ /dev/null
> @@ -1,679 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-or-later
> -/*
> - * Copyright (C) 2022, Alibaba Cloud
> - * Copyright (C) 2022, Bytedance Inc. All rights reserved.
> - */
> -#include <linux/pseudo_fs.h>
> -#include <linux/fscache.h>
> -#include "internal.h"
> -
> -static DEFINE_MUTEX(erofs_domain_list_lock);
> -static DEFINE_MUTEX(erofs_domain_cookies_lock);
> -static LIST_HEAD(erofs_domain_list);
> -static LIST_HEAD(erofs_domain_cookies_list);
> -static struct vfsmount *erofs_pseudo_mnt;
> -
> -static int erofs_anon_init_fs_context(struct fs_context *fc)
> -{
> -	return init_pseudo(fc, EROFS_SUPER_MAGIC) ? 0 : -ENOMEM;
> -}
> -
> -static struct file_system_type erofs_anon_fs_type = {
> -	.owner		= THIS_MODULE,
> -	.name           = "pseudo_erofs",
> -	.init_fs_context = erofs_anon_init_fs_context,
> -	.kill_sb        = kill_anon_super,
> -};
> -
> -struct erofs_fscache_io {
> -	struct netfs_cache_resources cres;
> -	struct iov_iter		iter;
> -	netfs_io_terminated_t	end_io;
> -	void			*private;
> -	refcount_t		ref;
> -};
> -
> -struct erofs_fscache_rq {
> -	struct address_space	*mapping;	/* The mapping being accessed */
> -	loff_t			start;		/* Start position */
> -	size_t			len;		/* Length of the request */
> -	size_t			submitted;	/* Length of submitted */
> -	short			error;		/* 0 or error that occurred */
> -	refcount_t		ref;
> -};
> -
> -static bool erofs_fscache_io_put(struct erofs_fscache_io *io)
> -{
> -	if (!refcount_dec_and_test(&io->ref))
> -		return false;
> -	if (io->cres.ops)
> -		io->cres.ops->end_operation(&io->cres);
> -	kfree(io);
> -	return true;
> -}
> -
> -static void erofs_fscache_req_complete(struct erofs_fscache_rq *req)
> -{
> -	struct folio *folio;
> -	bool failed = req->error;
> -	pgoff_t start_page = req->start / PAGE_SIZE;
> -	pgoff_t last_page = ((req->start + req->len) / PAGE_SIZE) - 1;
> -
> -	XA_STATE(xas, &req->mapping->i_pages, start_page);
> -
> -	rcu_read_lock();
> -	xas_for_each(&xas, folio, last_page) {
> -		if (xas_retry(&xas, folio))
> -			continue;
> -		if (!failed)
> -			folio_mark_uptodate(folio);
> -		/* Skip the entire folio before unlocking allows it to be split. */
> -		xas_advance(&xas, folio_next_index(folio) - 1);
> -		folio_unlock(folio);
> -	}
> -	rcu_read_unlock();
> -}
> -
> -static void erofs_fscache_req_put(struct erofs_fscache_rq *req)
> -{
> -	if (!refcount_dec_and_test(&req->ref))
> -		return;
> -	erofs_fscache_req_complete(req);
> -	kfree(req);
> -}
> -
> -static struct erofs_fscache_rq *erofs_fscache_req_alloc(struct address_space *mapping,
> -						loff_t start, size_t len)
> -{
> -	struct erofs_fscache_rq *req = kzalloc(sizeof(*req), GFP_KERNEL);
> -
> -	if (!req)
> -		return NULL;
> -	req->mapping = mapping;
> -	req->start = start;
> -	req->len = len;
> -	refcount_set(&req->ref, 1);
> -	return req;
> -}
> -
> -static void erofs_fscache_req_io_put(struct erofs_fscache_io *io)
> -{
> -	struct erofs_fscache_rq *req = io->private;
> -
> -	if (erofs_fscache_io_put(io))
> -		erofs_fscache_req_put(req);
> -}
> -
> -static void erofs_fscache_req_end_io(void *priv, ssize_t transferred_or_error)
> -{
> -	struct erofs_fscache_io *io = priv;
> -	struct erofs_fscache_rq *req = io->private;
> -
> -	if (IS_ERR_VALUE(transferred_or_error))
> -		req->error = transferred_or_error;
> -	erofs_fscache_req_io_put(io);
> -}
> -
> -static struct erofs_fscache_io *erofs_fscache_req_io_alloc(struct erofs_fscache_rq *req)
> -{
> -	struct erofs_fscache_io *io = kzalloc(sizeof(*io), GFP_KERNEL);
> -
> -	if (!io)
> -		return NULL;
> -	io->end_io = erofs_fscache_req_end_io;
> -	io->private = req;
> -	refcount_inc(&req->ref);
> -	refcount_set(&io->ref, 1);
> -	return io;
> -}
> -
> -/*
> - * Read data from fscache described by cookie at pstart physical address
> - * offset, and fill the read data into buffer described by io->iter.
> - */
> -static int erofs_fscache_read_io_async(struct fscache_cookie *cookie,
> -		loff_t pstart, struct erofs_fscache_io *io)
> -{
> -	enum netfs_io_source source;
> -	struct netfs_cache_resources *cres = &io->cres;
> -	struct iov_iter *iter = &io->iter;
> -	int ret;
> -
> -	ret = fscache_begin_read_operation(cres, cookie);
> -	if (ret)
> -		return ret;
> -
> -	while (iov_iter_count(iter)) {
> -		size_t orig_count = iov_iter_count(iter), len = orig_count;
> -		unsigned long flags = 1 << NETFS_SREQ_ONDEMAND;
> -
> -		source = cres->ops->prepare_ondemand_read(cres,
> -				pstart, &len, LLONG_MAX, &flags, 0);
> -		if (WARN_ON(len == 0))
> -			source = NETFS_INVALID_READ;
> -		if (source != NETFS_READ_FROM_CACHE) {
> -			erofs_err(NULL, "prepare_ondemand_read failed (source %d)", source);
> -			return -EIO;
> -		}
> -
> -		iov_iter_truncate(iter, len);
> -		refcount_inc(&io->ref);
> -		ret = fscache_read(cres, pstart, iter, NETFS_READ_HOLE_FAIL,
> -				   io->end_io, io);
> -		if (ret == -EIOCBQUEUED)
> -			ret = 0;
> -		if (ret) {
> -			erofs_err(NULL, "fscache_read failed (ret %d)", ret);
> -			return ret;
> -		}
> -		if (WARN_ON(iov_iter_count(iter)))
> -			return -EIO;
> -
> -		iov_iter_reexpand(iter, orig_count - len);
> -		pstart += len;
> -	}
> -	return 0;
> -}
> -
> -struct erofs_fscache_bio {
> -	struct erofs_fscache_io io;
> -	struct bio bio;		/* w/o bdev to share bio_add_page/endio() */
> -	struct bio_vec bvecs[BIO_MAX_VECS];
> -};
> -
> -static void erofs_fscache_bio_endio(void *priv, ssize_t transferred_or_error)
> -{
> -	struct erofs_fscache_bio *io = priv;
> -
> -	if (IS_ERR_VALUE(transferred_or_error))
> -		io->bio.bi_status = errno_to_blk_status(transferred_or_error);
> -	bio_endio(&io->bio);
> -	BUILD_BUG_ON(offsetof(struct erofs_fscache_bio, io) != 0);
> -	erofs_fscache_io_put(&io->io);
> -}
> -
> -struct bio *erofs_fscache_bio_alloc(struct erofs_map_dev *mdev)
> -{
> -	struct erofs_fscache_bio *io;
> -
> -	io = kmalloc(sizeof(*io), GFP_KERNEL | __GFP_NOFAIL);
> -	bio_init(&io->bio, NULL, io->bvecs, BIO_MAX_VECS, REQ_OP_READ);
> -	io->io.private = mdev->m_dif->fscache->cookie;
> -	io->io.end_io = erofs_fscache_bio_endio;
> -	refcount_set(&io->io.ref, 1);
> -	return &io->bio;
> -}
> -
> -void erofs_fscache_submit_bio(struct bio *bio)
> -{
> -	struct erofs_fscache_bio *io = container_of(bio,
> -			struct erofs_fscache_bio, bio);
> -	int ret;
> -
> -	iov_iter_bvec(&io->io.iter, ITER_DEST, io->bvecs, bio->bi_vcnt,
> -		      bio->bi_iter.bi_size);
> -	ret = erofs_fscache_read_io_async(io->io.private,
> -				bio->bi_iter.bi_sector << 9, &io->io);
> -	erofs_fscache_io_put(&io->io);
> -	if (!ret)
> -		return;
> -	bio->bi_status = errno_to_blk_status(ret);
> -	bio_endio(bio);
> -}
> -
> -static int erofs_fscache_meta_read_folio(struct file *data, struct folio *folio)
> -{
> -	struct erofs_fscache *ctx = folio->mapping->host->i_private;
> -	int ret = -ENOMEM;
> -	struct erofs_fscache_rq *req;
> -	struct erofs_fscache_io *io;
> -
> -	req = erofs_fscache_req_alloc(folio->mapping,
> -				folio_pos(folio), folio_size(folio));
> -	if (!req) {
> -		folio_unlock(folio);
> -		return ret;
> -	}
> -
> -	io = erofs_fscache_req_io_alloc(req);
> -	if (!io) {
> -		req->error = ret;
> -		goto out;
> -	}
> -	iov_iter_xarray(&io->iter, ITER_DEST, &folio->mapping->i_pages,
> -			folio_pos(folio), folio_size(folio));
> -
> -	ret = erofs_fscache_read_io_async(ctx->cookie, folio_pos(folio), io);
> -	if (ret)
> -		req->error = ret;
> -
> -	erofs_fscache_req_io_put(io);
> -out:
> -	erofs_fscache_req_put(req);
> -	return ret;
> -}
> -
> -static int erofs_fscache_data_read_slice(struct erofs_fscache_rq *req)
> -{
> -	struct address_space *mapping = req->mapping;
> -	struct inode *inode = mapping->host;
> -	struct super_block *sb = inode->i_sb;
> -	struct erofs_fscache_io *io;
> -	struct erofs_map_blocks map;
> -	struct erofs_map_dev mdev;
> -	loff_t pos = req->start + req->submitted;
> -	size_t count;
> -	int ret;
> -
> -	map.m_la = pos;
> -	ret = erofs_map_blocks(inode, &map);
> -	if (ret)
> -		return ret;
> -
> -	if (map.m_flags & EROFS_MAP_META) {
> -		struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
> -		struct iov_iter iter;
> -		size_t size = map.m_llen;
> -		void *src;
> -
> -		src = erofs_read_metabuf(&buf, sb, map.m_pa,
> -					 erofs_inode_in_metabox(inode));
> -		if (IS_ERR(src))
> -			return PTR_ERR(src);
> -
> -		iov_iter_xarray(&iter, ITER_DEST, &mapping->i_pages, pos, PAGE_SIZE);
> -		if (copy_to_iter(src, size, &iter) != size) {
> -			erofs_put_metabuf(&buf);
> -			return -EFAULT;
> -		}
> -		iov_iter_zero(PAGE_SIZE - size, &iter);
> -		erofs_put_metabuf(&buf);
> -		req->submitted += PAGE_SIZE;
> -		return 0;
> -	}
> -
> -	count = req->len - req->submitted;
> -	if (!(map.m_flags & EROFS_MAP_MAPPED)) {
> -		struct iov_iter iter;
> -
> -		iov_iter_xarray(&iter, ITER_DEST, &mapping->i_pages, pos, count);
> -		iov_iter_zero(count, &iter);
> -		req->submitted += count;
> -		return 0;
> -	}
> -
> -	count = min_t(size_t, map.m_llen - (pos - map.m_la), count);
> -	DBG_BUGON(!count || count % PAGE_SIZE);
> -
> -	mdev = (struct erofs_map_dev) {
> -		.m_deviceid = map.m_deviceid,
> -		.m_pa = map.m_pa,
> -	};
> -	ret = erofs_map_dev(sb, &mdev);
> -	if (ret)
> -		return ret;
> -
> -	io = erofs_fscache_req_io_alloc(req);
> -	if (!io)
> -		return -ENOMEM;
> -	iov_iter_xarray(&io->iter, ITER_DEST, &mapping->i_pages, pos, count);
> -	ret = erofs_fscache_read_io_async(mdev.m_dif->fscache->cookie,
> -			mdev.m_pa + (pos - map.m_la), io);
> -	erofs_fscache_req_io_put(io);
> -
> -	req->submitted += count;
> -	return ret;
> -}
> -
> -static int erofs_fscache_data_read(struct erofs_fscache_rq *req)
> -{
> -	int ret;
> -
> -	do {
> -		ret = erofs_fscache_data_read_slice(req);
> -		if (ret)
> -			req->error = ret;
> -	} while (!ret && req->submitted < req->len);
> -	return ret;
> -}
> -
> -static int erofs_fscache_read_folio(struct file *file, struct folio *folio)
> -{
> -	struct erofs_fscache_rq *req;
> -	int ret;
> -
> -	req = erofs_fscache_req_alloc(folio->mapping,
> -			folio_pos(folio), folio_size(folio));
> -	if (!req) {
> -		folio_unlock(folio);
> -		return -ENOMEM;
> -	}
> -
> -	ret = erofs_fscache_data_read(req);
> -	erofs_fscache_req_put(req);
> -	return ret;
> -}
> -
> -static void erofs_fscache_readahead(struct readahead_control *rac)
> -{
> -	struct erofs_fscache_rq *req;
> -
> -	if (!readahead_count(rac))
> -		return;
> -
> -	req = erofs_fscache_req_alloc(rac->mapping,
> -			readahead_pos(rac), readahead_length(rac));
> -	if (!req)
> -		return;
> -
> -	/* The request completion will drop refs on the folios. */
> -	while (readahead_folio(rac))
> -		;
> -
> -	erofs_fscache_data_read(req);
> -	erofs_fscache_req_put(req);
> -}
> -
> -static const struct address_space_operations erofs_fscache_meta_aops = {
> -	.read_folio = erofs_fscache_meta_read_folio,
> -};
> -
> -const struct address_space_operations erofs_fscache_access_aops = {
> -	.read_folio = erofs_fscache_read_folio,
> -	.readahead = erofs_fscache_readahead,
> -};
> -
> -static void erofs_fscache_domain_put(struct erofs_domain *domain)
> -{
> -	mutex_lock(&erofs_domain_list_lock);
> -	if (refcount_dec_and_test(&domain->ref)) {
> -		list_del(&domain->list);
> -		if (list_empty(&erofs_domain_list)) {
> -			kern_unmount(erofs_pseudo_mnt);
> -			erofs_pseudo_mnt = NULL;
> -		}
> -		fscache_relinquish_volume(domain->volume, NULL, false);
> -		mutex_unlock(&erofs_domain_list_lock);
> -		kfree(domain->domain_id);
> -		kfree(domain);
> -		return;
> -	}
> -	mutex_unlock(&erofs_domain_list_lock);
> -}
> -
> -static int erofs_fscache_register_volume(struct super_block *sb)
> -{
> -	struct erofs_sb_info *sbi = EROFS_SB(sb);
> -	char *domain_id = sbi->domain_id;
> -	struct fscache_volume *volume;
> -	char *name;
> -	int ret = 0;
> -
> -	name = kasprintf(GFP_KERNEL, "erofs,%s",
> -			 domain_id ? domain_id : sbi->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;
> -}
> -
> -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->domain_id, GFP_KERNEL);
> -	if (!domain->domain_id) {
> -		kfree(domain);
> -		return -ENOMEM;
> -	}
> -
> -	err = erofs_fscache_register_volume(sb);
> -	if (err)
> -		goto out;
> -
> -	if (!erofs_pseudo_mnt) {
> -		struct vfsmount *mnt = kern_mount(&erofs_anon_fs_type);
> -		if (IS_ERR(mnt)) {
> -			err = PTR_ERR(mnt);
> -			goto out;
> -		}
> -		erofs_pseudo_mnt = mnt;
> -	}
> -
> -	domain->volume = sbi->volume;
> -	refcount_set(&domain->ref, 1);
> -	list_add(&domain->list, &erofs_domain_list);
> -	sbi->domain = domain;
> -	return 0;
> -out:
> -	kfree(domain->domain_id);
> -	kfree(domain);
> -	return err;
> -}
> -
> -static 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->domain_id)) {
> -			sbi->domain = domain;
> -			sbi->volume = domain->volume;
> -			refcount_inc(&domain->ref);
> -			mutex_unlock(&erofs_domain_list_lock);
> -			return 0;
> -		}
> -	}
> -	err = erofs_fscache_init_domain(sb);
> -	mutex_unlock(&erofs_domain_list_lock);
> -	return err;
> -}
> -
> -static struct erofs_fscache *erofs_fscache_acquire_cookie(struct super_block *sb,
> -						char *name, unsigned int flags)
> -{
> -	struct fscache_volume *volume = EROFS_SB(sb)->volume;
> -	struct erofs_fscache *ctx;
> -	struct fscache_cookie *cookie;
> -	struct super_block *isb;
> -	struct inode *inode;
> -	int ret;
> -
> -	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
> -	if (!ctx)
> -		return ERR_PTR(-ENOMEM);
> -	INIT_LIST_HEAD(&ctx->node);
> -	refcount_set(&ctx->ref, 1);
> -
> -	cookie = fscache_acquire_cookie(volume, FSCACHE_ADV_WANT_CACHE_SIZE,
> -					name, strlen(name), NULL, 0, 0);
> -	if (!cookie) {
> -		erofs_err(sb, "failed to get cookie for %s", name);
> -		ret = -EINVAL;
> -		goto err;
> -	}
> -	fscache_use_cookie(cookie, false);
> -
> -	/*
> -	 * Allocate anonymous inode in global pseudo mount for shareable blobs,
> -	 * so that they are accessible among erofs fs instances.
> -	 */
> -	isb = flags & EROFS_REG_COOKIE_SHARE ? erofs_pseudo_mnt->mnt_sb : sb;
> -	inode = new_inode(isb);
> -	if (!inode) {
> -		erofs_err(sb, "failed to get anon inode for %s", name);
> -		ret = -ENOMEM;
> -		goto err_cookie;
> -	}
> -
> -	inode->i_size = OFFSET_MAX;
> -	inode->i_mapping->a_ops = &erofs_fscache_meta_aops;
> -	mapping_set_gfp_mask(inode->i_mapping, GFP_KERNEL);
> -	inode->i_blkbits = EROFS_SB(sb)->blkszbits;
> -	inode->i_private = ctx;
> -
> -	ctx->cookie = cookie;
> -	ctx->inode = inode;
> -	return ctx;
> -
> -err_cookie:
> -	fscache_unuse_cookie(cookie, NULL, NULL);
> -	fscache_relinquish_cookie(cookie, false);
> -err:
> -	kfree(ctx);
> -	return ERR_PTR(ret);
> -}
> -
> -static void erofs_fscache_relinquish_cookie(struct erofs_fscache *ctx)
> -{
> -	fscache_unuse_cookie(ctx->cookie, NULL, NULL);
> -	fscache_relinquish_cookie(ctx->cookie, false);
> -	iput(ctx->inode);
> -	kfree(ctx->name);
> -	kfree(ctx);
> -}
> -
> -static struct erofs_fscache *erofs_domain_init_cookie(struct super_block *sb,
> -						char *name, unsigned int flags)
> -{
> -	struct erofs_fscache *ctx;
> -	struct erofs_domain *domain = EROFS_SB(sb)->domain;
> -
> -	ctx = erofs_fscache_acquire_cookie(sb, name, flags);
> -	if (IS_ERR(ctx))
> -		return ctx;
> -
> -	ctx->name = kstrdup(name, GFP_KERNEL);
> -	if (!ctx->name) {
> -		erofs_fscache_relinquish_cookie(ctx);
> -		return ERR_PTR(-ENOMEM);
> -	}
> -
> -	refcount_inc(&domain->ref);
> -	ctx->domain = domain;
> -	list_add(&ctx->node, &erofs_domain_cookies_list);
> -	return ctx;
> -}
> -
> -static struct erofs_fscache *erofs_domain_register_cookie(struct super_block *sb,
> -						char *name, unsigned int flags)
> -{
> -	struct erofs_fscache *ctx;
> -	struct erofs_domain *domain = EROFS_SB(sb)->domain;
> -
> -	flags |= EROFS_REG_COOKIE_SHARE;
> -	mutex_lock(&erofs_domain_cookies_lock);
> -	list_for_each_entry(ctx, &erofs_domain_cookies_list, node) {
> -		if (ctx->domain != domain || strcmp(ctx->name, name))
> -			continue;
> -		if (!(flags & EROFS_REG_COOKIE_NEED_NOEXIST)) {
> -			refcount_inc(&ctx->ref);
> -		} else {
> -			erofs_err(sb, "%s already exists in domain %s", name,
> -				  domain->domain_id);
> -			ctx = ERR_PTR(-EEXIST);
> -		}
> -		mutex_unlock(&erofs_domain_cookies_lock);
> -		return ctx;
> -	}
> -	ctx = erofs_domain_init_cookie(sb, name, flags);
> -	mutex_unlock(&erofs_domain_cookies_lock);
> -	return ctx;
> -}
> -
> -struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
> -						    char *name,
> -						    unsigned int flags)
> -{
> -	if (EROFS_SB(sb)->domain_id)
> -		return erofs_domain_register_cookie(sb, name, flags);
> -	return erofs_fscache_acquire_cookie(sb, name, flags);
> -}
> -
> -void erofs_fscache_unregister_cookie(struct erofs_fscache *ctx)
> -{
> -	struct erofs_domain *domain = NULL;
> -
> -	if (!ctx)
> -		return;
> -	if (!ctx->domain)
> -		return erofs_fscache_relinquish_cookie(ctx);
> -
> -	mutex_lock(&erofs_domain_cookies_lock);
> -	if (refcount_dec_and_test(&ctx->ref)) {
> -		domain = ctx->domain;
> -		list_del(&ctx->node);
> -		erofs_fscache_relinquish_cookie(ctx);
> -	}
> -	mutex_unlock(&erofs_domain_cookies_lock);
> -	if (domain)
> -		erofs_fscache_domain_put(domain);
> -}
> -
> -int erofs_fscache_register_fs(struct super_block *sb)
> -{
> -	int ret;
> -	struct erofs_sb_info *sbi = EROFS_SB(sb);
> -	struct erofs_fscache *fscache;
> -	unsigned int flags = 0;
> -
> -	if (sbi->domain_id)
> -		ret = erofs_fscache_register_domain(sb);
> -	else
> -		ret = erofs_fscache_register_volume(sb);
> -	if (ret)
> -		return ret;
> -
> -	/*
> -	 * When shared domain is enabled, using NEED_NOEXIST to guarantee
> -	 * the primary data blob (aka fsid) is unique in the shared domain.
> -	 *
> -	 * For non-shared-domain case, fscache_acquire_volume() invoked by
> -	 * erofs_fscache_register_volume() has already guaranteed
> -	 * the uniqueness of primary data blob.
> -	 *
> -	 * Acquired domain/volume will be relinquished in kill_sb() on error.
> -	 */
> -	if (sbi->domain_id)
> -		flags |= EROFS_REG_COOKIE_NEED_NOEXIST;
> -	fscache = erofs_fscache_register_cookie(sb, sbi->fsid, flags);
> -	if (IS_ERR(fscache))
> -		return PTR_ERR(fscache);
> -
> -	sbi->dif0.fscache = fscache;
> -	return 0;
> -}
> -
> -void erofs_fscache_unregister_fs(struct super_block *sb)
> -{
> -	struct erofs_sb_info *sbi = EROFS_SB(sb);
> -
> -	erofs_fscache_unregister_cookie(sbi->dif0.fscache);
> -
> -	if (sbi->domain)
> -		erofs_fscache_domain_put(sbi->domain);
> -	else
> -		fscache_relinquish_volume(sbi->volume, NULL, false);
> -
> -	sbi->dif0.fscache = NULL;
> -	sbi->volume = NULL;
> -	sbi->domain = NULL;
> -}
> diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
> index 218ab22589228..07fab8d159292 100644
> --- a/fs/erofs/inode.c
> +++ b/fs/erofs/inode.c
> @@ -246,10 +246,6 @@ static int erofs_fill_inode(struct inode *inode)
>  #endif
>  	} else {
>  		inode->i_mapping->a_ops = &erofs_aops;
> -#ifdef CONFIG_EROFS_FS_ONDEMAND
> -		if (erofs_is_fscache_mode(inode->i_sb))
> -			inode->i_mapping->a_ops = &erofs_fscache_access_aops;
> -#endif
>  #ifdef CONFIG_EROFS_FS_BACKED_BY_FILE
>  		if (erofs_is_fileio_mode(EROFS_SB(inode->i_sb)))
>  			inode->i_mapping->a_ops = &erofs_fileio_aops;
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 845c71afb58d5..62f0d05e30393 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -41,7 +41,6 @@ typedef u64 erofs_blk_t;
>  
>  struct erofs_device_info {
>  	char *path;
> -	struct erofs_fscache *fscache;
>  	struct file *file;
>  	struct dax_device *dax_dev;
>  	u64 fsoff, dax_part_off;
> @@ -74,24 +73,6 @@ struct erofs_sb_lz4_info {
>  	u16 max_pclusterblks;	/* maximum physical blocks for LZ4 pclusters */
>  };
>  
> -struct erofs_domain {
> -	refcount_t ref;
> -	struct list_head list;
> -	struct fscache_volume *volume;
> -	char *domain_id;
> -};
> -
> -struct erofs_fscache {
> -	struct fscache_cookie *cookie;
> -	struct inode *inode;	/* anonymous inode for the blob */
> -
> -	/* used for share domain mode */
> -	struct erofs_domain *domain;
> -	struct list_head node;
> -	refcount_t ref;
> -	char *name;
> -};
> -
>  struct erofs_xattr_prefix_item {
>  	struct erofs_xattr_long_prefix *prefix;
>  	u8 infix_len;
> @@ -154,12 +135,6 @@ struct erofs_sb_info {
>  	struct kobject s_kobj;		/* /sys/fs/erofs/<devname> */
>  	struct completion s_kobj_unregister;
>  	erofs_off_t dir_ra_bytes;
> -
> -	/* fscache support */
> -	struct fscache_volume *volume;
> -	struct erofs_domain *domain;
> -	char *fsid;
> -	char *domain_id;
>  };
>  
>  #define EROFS_SB(sb) ((struct erofs_sb_info *)(sb)->s_fs_info)
> @@ -181,12 +156,6 @@ static inline bool erofs_is_fileio_mode(struct erofs_sb_info *sbi)
>  	return IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) && sbi->dif0.file;
>  }
>  
> -static inline bool erofs_is_fscache_mode(struct super_block *sb)
> -{
> -	return IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) &&
> -			!erofs_is_fileio_mode(EROFS_SB(sb)) && !sb->s_bdev;
> -}
> -
>  enum {
>  	EROFS_ZIP_CACHE_DISABLED,
>  	EROFS_ZIP_CACHE_READAHEAD,
> @@ -385,11 +354,9 @@ struct erofs_map_dev {
>  };
>  
>  extern const struct super_operations erofs_sops;
> -
>  extern const struct address_space_operations erofs_aops;
>  extern const struct address_space_operations erofs_fileio_aops;
>  extern const struct address_space_operations z_erofs_aops;
> -extern const struct address_space_operations erofs_fscache_access_aops;
>  
>  extern const struct inode_operations erofs_generic_iops;
>  extern const struct inode_operations erofs_symlink_iops;
> @@ -401,10 +368,6 @@ extern const struct file_operations erofs_dir_fops;
>  
>  extern const struct iomap_ops z_erofs_iomap_report_ops;
>  
> -/* flags for erofs_fscache_register_cookie() */
> -#define EROFS_REG_COOKIE_SHARE		0x0001
> -#define EROFS_REG_COOKIE_NEED_NOEXIST	0x0002
> -
>  void *erofs_read_metadata(struct super_block *sb, struct erofs_buf *buf,
>  			  erofs_off_t *offset, int *lengthp);
>  void erofs_unmap_metabuf(struct erofs_buf *buf);
> @@ -499,36 +462,6 @@ static inline struct bio *erofs_fileio_bio_alloc(struct erofs_map_dev *mdev) { r
>  static inline void erofs_fileio_submit_bio(struct bio *bio) {}
>  #endif
>  
> -#ifdef CONFIG_EROFS_FS_ONDEMAND
> -int erofs_fscache_register_fs(struct super_block *sb);
> -void erofs_fscache_unregister_fs(struct super_block *sb);
> -
> -struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
> -					char *name, unsigned int flags);
> -void erofs_fscache_unregister_cookie(struct erofs_fscache *fscache);
> -struct bio *erofs_fscache_bio_alloc(struct erofs_map_dev *mdev);
> -void erofs_fscache_submit_bio(struct bio *bio);
> -#else
> -static inline int erofs_fscache_register_fs(struct super_block *sb)
> -{
> -	return -EOPNOTSUPP;
> -}
> -static inline void erofs_fscache_unregister_fs(struct super_block *sb) {}
> -
> -static inline
> -struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
> -					char *name, unsigned int flags)
> -{
> -	return ERR_PTR(-EOPNOTSUPP);
> -}
> -
> -static inline void erofs_fscache_unregister_cookie(struct erofs_fscache *fscache)
> -{
> -}
> -static inline struct bio *erofs_fscache_bio_alloc(struct erofs_map_dev *mdev) { return NULL; }
> -static inline void erofs_fscache_submit_bio(struct bio *bio) {}
> -#endif
> -
>  long erofs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg);
>  long erofs_compat_ioctl(struct file *filp, unsigned int cmd,
>  			unsigned long arg);
> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
> index e6725e9847bed..18048719aab58 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -137,7 +137,6 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
>  			     struct erofs_device_info *dif, erofs_off_t *pos)
>  {
>  	struct erofs_sb_info *sbi = EROFS_SB(sb);
> -	struct erofs_fscache *fscache;
>  	struct erofs_deviceslot *dis;
>  	struct file *file;
>  	bool _48bit;
> @@ -156,12 +155,7 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
>  			return -ENOMEM;
>  	}
>  
> -	if (erofs_is_fscache_mode(sb)) {
> -		fscache = erofs_fscache_register_cookie(sb, dif->path, 0);
> -		if (IS_ERR(fscache))
> -			return PTR_ERR(fscache);
> -		dif->fscache = fscache;
> -	} else if (!sbi->devs->flatdev) {
> +	if (!sbi->devs->flatdev) {
>  		file = erofs_is_fileio_mode(sbi) ?
>  				filp_open(dif->path, O_RDONLY | O_LARGEFILE, 0) :
>  				bdev_file_open_by_path(dif->path,
> @@ -227,7 +221,7 @@ static int erofs_scan_devices(struct super_block *sb,
>  	if (!ondisk_extradevs)
>  		return 0;
>  
> -	if (!sbi->devs->extra_devices && !erofs_is_fscache_mode(sb))
> +	if (!sbi->devs->extra_devices)
>  		sbi->devs->flatdev = true;
>  
>  	sbi->device_id_mask = roundup_pow_of_two(ondisk_extradevs + 1) - 1;
> @@ -368,8 +362,6 @@ static int erofs_read_superblock(struct super_block *sb)
>  		erofs_info(sb, "EXPERIMENTAL 48-bit layout support in use. Use at your own risk!");
>  	if (erofs_sb_has_metabox(sbi))
>  		erofs_info(sb, "EXPERIMENTAL metadata compression support in use. Use at your own risk!");
> -	if (erofs_is_fscache_mode(sb))
> -		erofs_info(sb, "[deprecated] fscache-based on-demand read feature in use. Use at your own risk!");
>  out:
>  	erofs_put_metabuf(&buf);
>  	return ret;
> @@ -391,7 +383,7 @@ static void erofs_default_options(struct erofs_sb_info *sbi)
>  
>  enum {
>  	Opt_user_xattr, Opt_acl, Opt_cache_strategy, Opt_dax, Opt_dax_enum,
> -	Opt_device, Opt_fsid, Opt_domain_id, Opt_directio, Opt_fsoffset,
> +	Opt_device, Opt_domain_id, Opt_directio, Opt_fsoffset,
>  };
>  
>  static const struct constant_table erofs_param_cache_strategy[] = {
> @@ -415,7 +407,6 @@ static const struct fs_parameter_spec erofs_fs_parameters[] = {
>  	fsparam_flag("dax",             Opt_dax),
>  	fsparam_enum("dax",		Opt_dax_enum, erofs_dax_param_enums),
>  	fsparam_string("device",	Opt_device),
> -	fsparam_string("fsid",		Opt_fsid),
>  	fsparam_string("domain_id",	Opt_domain_id),
>  	fsparam_flag_no("directio",	Opt_directio),
>  	fsparam_u64("fsoffset",		Opt_fsoffset),
> @@ -513,25 +504,9 @@ static int erofs_fc_parse_param(struct fs_context *fc,
>  		}
>  		++sbi->devs->extra_devices;
>  		break;
> -#ifdef CONFIG_EROFS_FS_ONDEMAND
> -	case Opt_fsid:
> -		kfree(sbi->fsid);
> -		sbi->fsid = kstrdup(param->string, GFP_KERNEL);
> -		if (!sbi->fsid)
> -			return -ENOMEM;
> -		break;
> -	case Opt_domain_id:
> -		kfree(sbi->domain_id);
> -		sbi->domain_id = kstrdup(param->string, GFP_KERNEL);
> -		if (!sbi->domain_id)
> -			return -ENOMEM;
> -		break;
> -#else
> -	case Opt_fsid:
>  	case Opt_domain_id:
>  		errorfc(fc, "%s option not supported", erofs_fs_parameters[opt].name);
>  		break;
> -#endif
>  	case Opt_directio:
>  #ifdef CONFIG_EROFS_FS_BACKED_BY_FILE
>  		if (result.boolean)
> @@ -620,12 +595,7 @@ static void erofs_set_sysfs_name(struct super_block *sb)
>  {
>  	struct erofs_sb_info *sbi = EROFS_SB(sb);
>  
> -	if (sbi->domain_id)
> -		super_set_sysfs_name_generic(sb, "%s,%s", sbi->domain_id,
> -					     sbi->fsid);
> -	else if (sbi->fsid)
> -		super_set_sysfs_name_generic(sb, "%s", sbi->fsid);
> -	else if (erofs_is_fileio_mode(sbi))
> +	if (erofs_is_fileio_mode(sbi))
>  		super_set_sysfs_name_generic(sb, "%s",
>  					     bdi_dev_name(sb->s_bdi));
>  	else
> @@ -671,11 +641,6 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  		sb->s_blocksize = PAGE_SIZE;
>  		sb->s_blocksize_bits = PAGE_SHIFT;
>  
> -		if (erofs_is_fscache_mode(sb)) {
> -			err = erofs_fscache_register_fs(sb);
> -			if (err)
> -				return err;
> -		}
>  		err = super_setup_bdi(sb);
>  		if (err)
>  			return err;
> @@ -694,11 +659,6 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  		return err;
>  
>  	if (sb->s_blocksize_bits != sbi->blkszbits) {
> -		if (erofs_is_fscache_mode(sb)) {
> -			errorfc(fc, "unsupported blksize for fscache mode");
> -			return -EINVAL;
> -		}
> -
>  		if (erofs_is_fileio_mode(sbi)) {
>  			sb->s_blocksize = 1 << sbi->blkszbits;
>  			sb->s_blocksize_bits = sbi->blkszbits;
> @@ -707,14 +667,9 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  			return -EINVAL;
>  		}
>  	}
> -
> -	if (sbi->dif0.fsoff) {
> -		if (sbi->dif0.fsoff & (sb->s_blocksize - 1))
> -			return invalfc(fc, "fsoffset %llu is not aligned to block size %lu",
> -				       sbi->dif0.fsoff, sb->s_blocksize);
> -		if (erofs_is_fscache_mode(sb))
> -			return invalfc(fc, "cannot use fsoffset in fscache mode");
> -	}
> +	if (sbi->dif0.fsoff & (sb->s_blocksize - 1))
> +		return invalfc(fc, "fsoffset %llu is not aligned to block size %lu",
> +			       sbi->dif0.fsoff, sb->s_blocksize);
>  
>  	if (test_opt(&sbi->opt, DAX_ALWAYS) && sbi->blkszbits != PAGE_SHIFT) {
>  		erofs_info(sb, "unsupported blocksize for DAX");
> @@ -778,17 +733,14 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
>  
>  static int erofs_fc_get_tree(struct fs_context *fc)
>  {
> -	struct erofs_sb_info *sbi = fc->s_fs_info;
>  	int ret;
>  
> -	if (IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid)
> -		return get_tree_nodev(fc, erofs_fc_fill_super);
> -
>  	ret = get_tree_bdev_flags(fc, erofs_fc_fill_super,
>  		IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) ?
>  			GET_TREE_BDEV_QUIET_LOOKUP : 0);
>  #ifdef CONFIG_EROFS_FS_BACKED_BY_FILE
>  	if (ret == -ENOTBLK) {
> +		struct erofs_sb_info *sbi = fc->s_fs_info;
>  		struct file *file;
>  
>  		if (!fc->source)
> @@ -814,9 +766,6 @@ static int erofs_fc_reconfigure(struct fs_context *fc)
>  
>  	DBG_BUGON(!sb_rdonly(sb));
>  
> -	if (new_sbi->fsid || new_sbi->domain_id)
> -		erofs_info(sb, "ignoring reconfiguration for fsid|domain_id.");
> -
>  	if (test_opt(&new_sbi->opt, POSIX_ACL))
>  		fc->sb_flags |= SB_POSIXACL;
>  	else
> @@ -835,8 +784,6 @@ static int erofs_release_device_info(int id, void *ptr, void *data)
>  	fs_put_dax(dif->dax_dev, NULL);
>  	if (dif->file)
>  		fput(dif->file);
> -	erofs_fscache_unregister_cookie(dif->fscache);
> -	dif->fscache = NULL;
>  	kfree(dif->path);
>  	kfree(dif);
>  	return 0;
> @@ -854,8 +801,6 @@ static void erofs_free_dev_context(struct erofs_dev_context *devs)
>  static void erofs_sb_free(struct erofs_sb_info *sbi)
>  {
>  	erofs_free_dev_context(sbi->devs);
> -	kfree(sbi->fsid);
> -	kfree(sbi->domain_id);
>  	if (sbi->dif0.file)
>  		fput(sbi->dif0.file);
>  	kfree(sbi->volume_name);
> @@ -915,14 +860,12 @@ static void erofs_kill_sb(struct super_block *sb)
>  {
>  	struct erofs_sb_info *sbi = EROFS_SB(sb);
>  
> -	if ((IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) && sbi->fsid) ||
> -	    sbi->dif0.file)
> +	if (sbi->dif0.file)
>  		kill_anon_super(sb);
>  	else
>  		kill_block_super(sb);
>  	erofs_drop_internal_inodes(sbi);
>  	fs_put_dax(sbi->dif0.dax_dev, NULL);
> -	erofs_fscache_unregister_fs(sb);
>  	erofs_sb_free(sbi);
>  	sb->s_fs_info = NULL;
>  }
> @@ -937,7 +880,6 @@ static void erofs_put_super(struct super_block *sb)
>  	erofs_drop_internal_inodes(sbi);
>  	erofs_free_dev_context(sbi->devs);
>  	sbi->devs = NULL;
> -	erofs_fscache_unregister_fs(sb);
>  }
>  
>  static struct file_system_type erofs_fs_type = {
> @@ -1044,12 +986,6 @@ static int erofs_show_options(struct seq_file *seq, struct dentry *root)
>  		seq_puts(seq, ",dax=never");
>  	if (erofs_is_fileio_mode(sbi) && test_opt(opt, DIRECT_IO))
>  		seq_puts(seq, ",directio");
> -#ifdef CONFIG_EROFS_FS_ONDEMAND
> -	if (sbi->fsid)
> -		seq_printf(seq, ",fsid=%s", sbi->fsid);
> -	if (sbi->domain_id)
> -		seq_printf(seq, ",domain_id=%s", sbi->domain_id);
> -#endif
>  	if (sbi->dif0.fsoff)
>  		seq_printf(seq, ",fsoffset=%llu", sbi->dif0.fsoff);
>  	return 0;
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index 0af259e22026f..9214f3c0e851e 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -1699,8 +1699,6 @@ static void z_erofs_submit_queue(struct z_erofs_frontend *f,
>  drain_io:
>  				if (erofs_is_fileio_mode(EROFS_SB(sb)))
>  					erofs_fileio_submit_bio(bio);
> -				else if (erofs_is_fscache_mode(sb))
> -					erofs_fscache_submit_bio(bio);
>  				else
>  					submit_bio(bio);
>  
> @@ -1729,8 +1727,6 @@ static void z_erofs_submit_queue(struct z_erofs_frontend *f,
>  			if (!bio) {
>  				if (erofs_is_fileio_mode(EROFS_SB(sb)))
>  					bio = erofs_fileio_bio_alloc(&mdev);
> -				else if (erofs_is_fscache_mode(sb))
> -					bio = erofs_fscache_bio_alloc(&mdev);
>  				else
>  					bio = bio_alloc(mdev.m_bdev, BIO_MAX_VECS,
>  							REQ_OP_READ, GFP_NOIO);
> @@ -1759,8 +1755,6 @@ static void z_erofs_submit_queue(struct z_erofs_frontend *f,
>  	if (bio) {
>  		if (erofs_is_fileio_mode(EROFS_SB(sb)))
>  			erofs_fileio_submit_bio(bio);
> -		else if (erofs_is_fscache_mode(sb))
> -			erofs_fscache_submit_bio(bio);
>  		else
>  			submit_bio(bio);
>  	}

Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

[Greg KH]

On Tue, Oct 13, 2026 at 09:28:44AM +0200, Gao Xiang wrote:
> Hi Sasha,
> 
> I'm not sure why we need to backport this into stable kernels, as there
> are users who use EROFS over fscache on these stable kernels.
> 
> The functionality works and it's a breaking change.  Could you please
> kindly tell why?

Why would you have a breaking change in Linus's tree?  We never break
existing users, so how was this ever accepted in mainline?

As this removal fixes known bugs, isn't that a good thing for those
older users as well?  Why would you want them to run broken systems?

thanks,

greg k-h

Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

[Gao Xiang]

Hi Greg,

On Tue, Oct 13, 2026 at 09:59:58AM +0200, Greg KH wrote:
> On Tue, Oct 13, 2026 at 09:28:44AM +0200, Gao Xiang wrote:
> > Hi Sasha,
> > 
> > I'm not sure why we need to backport this into stable kernels, as there
> > are users who use EROFS over fscache on these stable kernels.
> > 
> > The functionality works and it's a breaking change.  Could you please
> > kindly tell why?
> 
> Why would you have a breaking change in Linus's tree?  We never break
> existing users, so how was this ever accepted in mainline?

Because the similar + better functionality "erofs over fanotify" is
already available in the recent upstream, and it has simpler interfaces
than "erofs over fscache.", so we don't actually break users as long
as one of those functionalities exist ("erofs over fanotify" or
"erofs over fscache".  Many stable kernels don't support "erofs over
fsnotify", so backport this commit will make existing users using
old stable kernels have no choice (no "erofs over fanotify" nor
"erofs over fscache").

The commit message is already described well I think. 

> 
> As this removal fixes known bugs, isn't that a good thing for those
> older users as well?  Why would you want them to run broken systems?

I think it depends on the importance of the bug, at least "erofs over
fscache" is usable (and it's used by vendors) on stable kernels, but
it's unneeded to address every edge case found by LLMs since I mostly
think it doesn't impact the real use case, and as I said, we have
a new unique interface ("erofs over fanotify") now, but only on very
latest kernels.

Also there could always be breaking changes for various reasons (e.g.
obsolete/dispute filesystem breaking changes these years like
bcachefs, etc), will these commits be backported to all stable kernels
too?

Thanks,
Gao Xiang


>
> thanks,
> 
> greg k-h
> 

Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

[Greg KH]

On Tue, Oct 13, 2026 at 10:16:29AM +0200, Gao Xiang wrote:
> Hi Greg,
> 
> On Tue, Oct 13, 2026 at 09:59:58AM +0200, Greg KH wrote:
> > On Tue, Oct 13, 2026 at 09:28:44AM +0200, Gao Xiang wrote:
> > > Hi Sasha,
> > > 
> > > I'm not sure why we need to backport this into stable kernels, as there
> > > are users who use EROFS over fscache on these stable kernels.
> > > 
> > > The functionality works and it's a breaking change.  Could you please
> > > kindly tell why?
> > 
> > Why would you have a breaking change in Linus's tree?  We never break
> > existing users, so how was this ever accepted in mainline?
> 
> Because the similar + better functionality "erofs over fanotify" is
> already available in the recent upstream, and it has simpler interfaces
> than "erofs over fscache.", so we don't actually break users as long
> as one of those functionalities exist ("erofs over fanotify" or
> "erofs over fscache".  Many stable kernels don't support "erofs over
> fsnotify", so backport this commit will make existing users using
> old stable kernels have no choice (no "erofs over fanotify" nor
> "erofs over fscache").
> 
> The commit message is already described well I think. 
> 
> > 
> > As this removal fixes known bugs, isn't that a good thing for those
> > older users as well?  Why would you want them to run broken systems?
> 
> I think it depends on the importance of the bug, at least "erofs over
> fscache" is usable (and it's used by vendors) on stable kernels, but
> it's unneeded to address every edge case found by LLMs since I mostly
> think it doesn't impact the real use case, and as I said, we have
> a new unique interface ("erofs over fanotify") now, but only on very
> latest kernels.
> 
> Also there could always be breaking changes for various reasons (e.g.
> obsolete/dispute filesystem breaking changes these years like
> bcachefs, etc), will these commits be backported to all stable kernels
> too?

Sometimes, yes they are.

But this makes sense, I'll go drop this patch now, thanks.

greg k-h

Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

[Michael Bommarito]

For context, the original bug I found can hit both 100% deterministic
local DoS and a textbook UAF on kmalloc-128 slab that requires timing,
but I don't think an LPE can be ruled out...

Since it is reachable by an ordinary read() on Nydus or others that
enabled ondemand in Kconfig, I think it is worth thinking about what to
do for all of the pre-deprecation users (even if it's just comms).

I would defer to Gao, but I sent a minimal fix in June that can
close the UAF without any other breaking changes.

Thanks,
Michael Bommarito

Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

[Gao Xiang]

Hi Michael,

On Tue, Oct 13, 2026 at 07:10:11AM -0400, Michael Bommarito wrote:
> For context, the original bug I found can hit both 100% deterministic
> local DoS and a textbook UAF on kmalloc-128 slab that requires timing,
> but I don't think an LPE can be ruled out...
> 
> Since it is reachable by an ordinary read() on Nydus or others that
> enabled ondemand in Kconfig, I think it is worth thinking about what to
> do for all of the pre-deprecation users (even if it's just comms).
> 
> I would defer to Gao, but I sent a minimal fix in June that can
> close the UAF without any other breaking changes.

Do you mean this one?
https://lore.kernel.org/r/20260619135800.1594811-1-michael.bommarito@gmail.com

As I requested months ago, could you please provide a reproducer first
so I can play with your patch.

If you provide a minimal reproducer, of course we could address this in
the stable kernels.

Thanks,
Gao Xiang

> 
> Thanks,
> Michael Bommarito
> 

Re: Patch "erofs: remove fscache backend entirely" has been added to the 6.18-stable tree

[Gao Xiang]

On Tue, Oct 13, 2026 at 12:37:56PM +0200, Greg KH wrote:
> On Tue, Oct 13, 2026 at 10:16:29AM +0200, Gao Xiang wrote:
> > Hi Greg,
> > 
> > On Tue, Oct 13, 2026 at 09:59:58AM +0200, Greg KH wrote:
> > > On Tue, Oct 13, 2026 at 09:28:44AM +0200, Gao Xiang wrote:
> > > > Hi Sasha,
> > > > 
> > > > I'm not sure why we need to backport this into stable kernels, as there
> > > > are users who use EROFS over fscache on these stable kernels.
> > > > 
> > > > The functionality works and it's a breaking change.  Could you please
> > > > kindly tell why?
> > > 
> > > Why would you have a breaking change in Linus's tree?  We never break
> > > existing users, so how was this ever accepted in mainline?
> > 
> > Because the similar + better functionality "erofs over fanotify" is
> > already available in the recent upstream, and it has simpler interfaces
> > than "erofs over fscache.", so we don't actually break users as long
> > as one of those functionalities exist ("erofs over fanotify" or
> > "erofs over fscache".  Many stable kernels don't support "erofs over
> > fsnotify", so backport this commit will make existing users using
> > old stable kernels have no choice (no "erofs over fanotify" nor
> > "erofs over fscache").
> > 
> > The commit message is already described well I think. 
> > 
> > > 
> > > As this removal fixes known bugs, isn't that a good thing for those
> > > older users as well?  Why would you want them to run broken systems?
> > 
> > I think it depends on the importance of the bug, at least "erofs over
> > fscache" is usable (and it's used by vendors) on stable kernels, but
> > it's unneeded to address every edge case found by LLMs since I mostly
> > think it doesn't impact the real use case, and as I said, we have
> > a new unique interface ("erofs over fanotify") now, but only on very
> > latest kernels.
> > 
> > Also there could always be breaking changes for various reasons (e.g.
> > obsolete/dispute filesystem breaking changes these years like
> > bcachefs, etc), will these commits be backported to all stable kernels
> > too?
> 
> Sometimes, yes they are.
> 
> But this makes sense, I'll go drop this patch now, thanks.

Thanks, Greg.  As I said, "erofs over fscache" is still used by
Xiaomi on old stable kernels for example:
https://lore.kernel.org/all/20260923084823.496741-1-hwenwur@gmail.com

But we prefer to use fanotify in recent kernels and it has
a simpler and unique interface than the old one.

There is no need to leave two same functionality features within
the same codebase, so we deprecated fscache two years ago, and
removed it months before so that we could sunset the old
interface over time.

I think another similar example is XFS v4 format, The kconfig says
that it will be removed in 2030 as well:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/xfs/Kconfig?h=v7.2#n51

Thanks,
Gao Xiang

> 
> greg k-h
>