Re: [PATCH RFC] fs: New zonefs file system

[Jeff Moyer <jmoyer@redhat.com>]

Hi, Damien,

Did you consider creating a shared library?  I bet that would also
ease application adoption for the use cases you're interested in, and
would have similar performance.

-Jeff

Damien Le Moal <damien.lemoal@wdc.com> writes:

> zonefs is a very simple file system exposing each zone of a zoned
> block device as a file. This is intended to simplify implementation of
> application zoned block device raw access support by allowing switching
> to the well known POSIX file API rather than relying on direct block
> device file ioctls and read/write. Zonefs, for instance, greatly
> simplifies the implementation of LSM (log-structured merge) tree
> structures (such as used in RocksDB and LevelDB) on zoned block devices
> by allowing SSTables to be stored in a zone file similarly to a regular
> file system architecture, hence reducing the amount of change needed in
> the application.
>
> Due to its simplicity, zonefs is in fact closer to a raw block device
> access interface than to a full feature POSIX file system. This RFC
> implementation uses Christoph's work on generic iomap writepage
> implementation and is based on Christoph's gfs2 tree available at
> http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/gfs2-iomap
>
> Zonefs on-disk metadata is reduced to a super block to store a magic
> number, a uuid and optional features flags and values. On mount, zonefs
> uses blkdev_report_zones() to obtain the device zone configuration and
> populates the mount point with a static file tree solely based on this
> information. E.g. file sizes come from zone write pointer offset managed
> by the device itself.
>
> The zone files created on mount have the following characteristics.
> 1) Files representing zones of the same type are grouped together
>    under a common directory:
>   * For conventional zones, the directory "cnv" is used.
>   * For sequential write zones, the directory "seq" is used.
>   These two directories are the only directories that exist in zonefs.
>   Users cannot create other directories and cannot rename nor delete
>   the "cnv" and "seq" directories.
> 2) The name of zone files is by default the number of the file within
>    the zone type directory, in order of increasing zone start sector.
> 3) The size of conventional zone files is fixed to the device zone size.
>    Conventional zone files cannot be truncated.
> 4) The size of sequential zone files represent the file zone write
>    pointer position relative to the zone start sector. Truncating these
>    files is allowed only down to 0, in wich case, the zone is reset to
>    rewind the file zone write pointer position to the start of the zone.
> 5) All read and write operations to files are not allowed beyond the
>    file zone size. Any access exceeding the zone size is failed with
>    the -EFBIG error.
> 6) Creating, deleting, renaming or modifying any attribute of files
>    and directories is not allowed. The only exception being the file
>    size of sequential zone files which can be modified by write
>    operations or truncation to 0.
>
> Several optional features of zonefs can be enabled at format time.
> * Conventional zone aggregation: contiguous conventional zones can be
>   agregated into a single larger file instead of multiple per-zone
>   files.
> * File naming: the default file number file name can be switched to
>   using the base-10 value of the file zone start sector.
> * File ownership: The owner UID and GID of zone files is by default 0
>   (root) but can be changed to any valid UID/GID.
> * File access permissions: the default 640 access permissions can be
>   changed.
>
> The mkzonefs tool is used to format zonefs. This tool will be available
> on Github at:
>
> https://github.com/westerndigitalcorporation/zonefs-tools
>
> Example: the following formats a host-managed SMR HDD with the
> conventional zone aggregation feature enabled.
>
> mkzonefs -o aggr_cnv /dev/sdX
> mount -t zonefs /dev/sdX /mnt
> ls -l /mnt/
> total 0
> dr-xr-xr-x 2 root root 0 Apr 11 13:00 cnv
> dr-xr-xr-x 2 root root 0 Apr 11 13:00 seq
>
> ls -l /mnt/cnv
> total 137363456
> -rw-rw---- 1 root root 140660178944 Apr 11 13:00 0
>
> ls -Fal -v /mnt/seq
> total 14511243264
> dr-xr-xr-x 2 root root 15942528 Jul 10 11:53 ./
> drwxr-xr-x 4 root root     1152 Jul 10 11:53 ../
> -rw-r----- 1 root root        0 Jul 10 11:53 0
> -rw-r----- 1 root root 33554432 Jul 10 13:43 1
> -rw-r----- 1 root root        0 Jul 10 11:53 2
> -rw-r----- 1 root root        0 Jul 10 11:53 3
> ...
>
> The aggregated conventional zone file can be used as a regular file.
> Operations such as the following work.
>
> mkfs.ext4 /mnt/cnv/0
> mount -o loop /mnt/cnv/0 /data
>
> Contains contributions from Johannes Thumshirn <jthumshirn@suse.de>
> and Christoph Hellwig <hch@lst.de>.
>
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>  fs/Kconfig                 |    2 +
>  fs/Makefile                |    1 +
>  fs/zonefs/Kconfig          |    9 +
>  fs/zonefs/Makefile         |    4 +
>  fs/zonefs/super.c          | 1004 ++++++++++++++++++++++++++++++++++++
>  fs/zonefs/zonefs.h         |  190 +++++++
>  include/uapi/linux/magic.h |    1 +
>  7 files changed, 1211 insertions(+)
>  create mode 100644 fs/zonefs/Kconfig
>  create mode 100644 fs/zonefs/Makefile
>  create mode 100644 fs/zonefs/super.c
>  create mode 100644 fs/zonefs/zonefs.h
>
> diff --git a/fs/Kconfig b/fs/Kconfig
> index f1046cf6ad85..e48cc0e0efbb 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -41,6 +41,7 @@ source "fs/ocfs2/Kconfig"
>  source "fs/btrfs/Kconfig"
>  source "fs/nilfs2/Kconfig"
>  source "fs/f2fs/Kconfig"
> +source "fs/zonefs/Kconfig"
>  
>  config FS_DAX
>  	bool "Direct Access (DAX) support"
> @@ -262,6 +263,7 @@ source "fs/romfs/Kconfig"
>  source "fs/pstore/Kconfig"
>  source "fs/sysv/Kconfig"
>  source "fs/ufs/Kconfig"
> +source "fs/ufs/Kconfig"
>  
>  endif # MISC_FILESYSTEMS
>  
> diff --git a/fs/Makefile b/fs/Makefile
> index c9aea23aba56..02fcd528991b 100644
> --- a/fs/Makefile
> +++ b/fs/Makefile
> @@ -130,3 +130,4 @@ obj-$(CONFIG_F2FS_FS)		+= f2fs/
>  obj-$(CONFIG_CEPH_FS)		+= ceph/
>  obj-$(CONFIG_PSTORE)		+= pstore/
>  obj-$(CONFIG_EFIVAR_FS)		+= efivarfs/
> +obj-$(CONFIG_ZONEFS_FS)		+= zonefs/
> diff --git a/fs/zonefs/Kconfig b/fs/zonefs/Kconfig
> new file mode 100644
> index 000000000000..6490547e9763
> --- /dev/null
> +++ b/fs/zonefs/Kconfig
> @@ -0,0 +1,9 @@
> +config ZONEFS_FS
> +	tristate "zonefs filesystem support"
> +	depends on BLOCK
> +	depends on BLK_DEV_ZONED
> +	help
> +	  zonefs is a simple File System which exposes zones of a zoned block
> +	  device as files.
> +
> +	  If unsure, say N.
> diff --git a/fs/zonefs/Makefile b/fs/zonefs/Makefile
> new file mode 100644
> index 000000000000..75a380aa1ae1
> --- /dev/null
> +++ b/fs/zonefs/Makefile
> @@ -0,0 +1,4 @@
> +# SPDX-License-Identifier: GPL-2.0
> +obj-$(CONFIG_ZONEFS_FS) += zonefs.o
> +
> +zonefs-y	:= super.o
> diff --git a/fs/zonefs/super.c b/fs/zonefs/super.c
> new file mode 100644
> index 000000000000..0bf56f378a77
> --- /dev/null
> +++ b/fs/zonefs/super.c
> @@ -0,0 +1,1004 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Simple zone file system for zoned block devices.
> + *
> + * Copyright (C) 2019 Western Digital Corporation or its affiliates.
> + */
> +#include <linux/module.h>
> +#include <linux/fs.h>
> +#include <linux/magic.h>
> +#include <linux/iomap.h>
> +#include <linux/init.h>
> +#include <linux/slab.h>
> +#include <linux/blkdev.h>
> +#include <linux/statfs.h>
> +#include <linux/writeback.h>
> +#include <linux/quotaops.h>
> +#include <linux/seq_file.h>
> +#include <linux/parser.h>
> +#include <linux/uio.h>
> +#include <linux/mman.h>
> +#include <linux/sched/mm.h>
> +
> +#include "zonefs.h"
> +
> +static int zonefs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> +			      unsigned int flags, struct iomap *iomap)
> +{
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(inode->i_sb);
> +	loff_t max_isize = zonefs_file_max_size(inode);
> +	loff_t isize = i_size_read(inode);
> +
> +	/*
> +	 * For sequential zones, enforce direct IO writes. This is already
> +	 * checked when writes are issued, so warn about this here if we
> +	 * get buffered write to a sequential file inode.
> +	 */
> +	if (WARN_ON_ONCE(zonefs_file_is_seq(inode) && (flags & IOMAP_WRITE) &&
> +			 (!(flags & IOMAP_DIRECT))))
> +		return -EIO;
> +
> +	/* An IO cannot exceed the zone size */
> +	if (offset >= max_isize)
> +		return -EFBIG;
> +
> +	/* All blocks are always mapped */
> +	if (offset >= i_size_read(inode)) {
> +		length = min(length, max_isize - offset);
> +		iomap->type = IOMAP_UNWRITTEN;
> +	} else {
> +		length = min(length, isize - offset);
> +		iomap->type = IOMAP_MAPPED;
> +	}
> +	iomap->offset = offset & (~sbi->s_blocksize_mask);
> +	iomap->length = (offset + length + sbi->s_blocksize_mask) &
> +			(~sbi->s_blocksize_mask);
> +	iomap->addr = zonefs_file_addr(inode) + iomap->offset;
> +	iomap->bdev = inode->i_sb->s_bdev;
> +
> +	return 0;
> +}
> +
> +static const struct iomap_ops zonefs_iomap_ops = {
> +	.iomap_begin	= zonefs_iomap_begin,
> +};
> +
> +static int zonefs_readpage(struct file *unused, struct page *page)
> +{
> +	return iomap_readpage(page, &zonefs_iomap_ops);
> +}
> +
> +static int zonefs_readpages(struct file *unused, struct address_space *mapping,
> +			    struct list_head *pages, unsigned int nr_pages)
> +{
> +	return iomap_readpages(mapping, pages, nr_pages, &zonefs_iomap_ops);
> +}
> +
> +static int zonefs_map_blocks(struct iomap_writepage_ctx *wpc,
> +			     struct inode *inode, loff_t offset)
> +{
> +	if (offset >= wpc->iomap.offset &&
> +	    offset < wpc->iomap.offset + wpc->iomap.length)
> +		return 0;
> +
> +	memset(&wpc->iomap, 0, sizeof(wpc->iomap));
> +	return zonefs_iomap_begin(inode, offset, INT_MAX, 0, &wpc->iomap);
> +}
> +
> +static const struct iomap_writeback_ops zonefs_writeback_ops = {
> +	.map_blocks		= zonefs_map_blocks,
> +};
> +
> +static int zonefs_writepage(struct page *page, struct writeback_control *wbc)
> +{
> +	struct iomap_writepage_ctx wpc = { };
> +
> +	return iomap_writepage(page, wbc, &wpc, &zonefs_writeback_ops);
> +}
> +
> +static int zonefs_writepages(struct address_space *mapping,
> +			     struct writeback_control *wbc)
> +{
> +	struct iomap_writepage_ctx wpc = { };
> +
> +	return iomap_writepages(mapping, wbc, &wpc, &zonefs_writeback_ops);
> +}
> +
> +static const struct address_space_operations zonefs_file_aops = {
> +	.readpage		= zonefs_readpage,
> +	.readpages		= zonefs_readpages,
> +	.writepage		= zonefs_writepage,
> +	.writepages		= zonefs_writepages,
> +	.set_page_dirty		= iomap_set_page_dirty,
> +	.releasepage		= iomap_releasepage,
> +	.invalidatepage		= iomap_invalidatepage,
> +	.migratepage		= iomap_migrate_page,
> +	.is_partially_uptodate  = iomap_is_partially_uptodate,
> +	.error_remove_page	= generic_error_remove_page,
> +	.direct_IO		= noop_direct_IO,
> +};
> +
> +static int zonefs_truncate_seqfile(struct inode *inode)
> +{
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	int ret;
> +
> +	/* Serialize against page faults */
> +	down_write(&zi->i_mmap_sem);
> +
> +	ret = blkdev_reset_zones(inode->i_sb->s_bdev,
> +				 zonefs_file_addr(inode) >> SECTOR_SHIFT,
> +				 zonefs_file_max_size(inode) >> SECTOR_SHIFT,
> +				 GFP_KERNEL);
> +	if (ret) {
> +		zonefs_err(inode->i_sb,
> +			   "zonefs: Reset zone at %llu failed %d",
> +			   zonefs_file_addr(inode) >> SECTOR_SHIFT,
> +			   ret);
> +	} else {
> +		truncate_setsize(inode, 0);
> +		zi->i_wpoffset = 0;
> +	}
> +
> +	up_write(&zi->i_mmap_sem);
> +
> +	return ret;
> +}
> +
> +static int zonefs_inode_setattr(struct dentry *dentry, struct iattr *iattr)
> +{
> +	struct inode *inode = d_inode(dentry);
> +	int ret;
> +
> +	ret = setattr_prepare(dentry, iattr);
> +	if (ret)
> +		return ret;
> +
> +	if ((iattr->ia_valid & ATTR_UID &&
> +	     !uid_eq(iattr->ia_uid, inode->i_uid)) ||
> +	    (iattr->ia_valid & ATTR_GID &&
> +	     !gid_eq(iattr->ia_gid, inode->i_gid))) {
> +		ret = dquot_transfer(inode, iattr);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	if (iattr->ia_valid & ATTR_SIZE) {
> +		/* The size of conventional zone files cannot be changed */
> +		if (zonefs_file_is_conv(inode))
> +			return -EPERM;
> +
> +		/*
> +		 * For sequential zone files, we can only allow truncating to
> +		 * 0 size which is equivalent to a zone reset.
> +		 */
> +		if (iattr->ia_size != 0)
> +			return -EPERM;
> +
> +		ret = zonefs_truncate_seqfile(inode);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	setattr_copy(inode, iattr);
> +
> +	return 0;
> +}
> +
> +static const struct inode_operations zonefs_file_inode_operations = {
> +	.setattr	= zonefs_inode_setattr,
> +};
> +
> +/*
> + * Open a file.
> + */
> +static int zonefs_file_open(struct inode *inode, struct file *file)
> +{
> +	/*
> +	 * Note: here we can do an explicit open of the file zone,
> +	 * on the first open of the inode. The explicit close can be
> +	 * done on the last release (close) call for the inode.
> +	 */
> +
> +	return generic_file_open(inode, file);
> +}
> +
> +static int zonefs_file_fsync(struct file *file, loff_t start, loff_t end,
> +			     int datasync)
> +{
> +	struct inode *inode = file_inode(file);
> +	int ret;
> +
> +	/*
> +	 * Since only direct writes are allowed in sequential files, we only
> +	 * need a device flush for these files.
> +	 */
> +	if (zonefs_file_is_seq(inode))
> +		goto flush;
> +
> +	ret = file_write_and_wait_range(file, start, end);
> +	if (ret == 0)
> +		ret = file_check_and_advance_wb_err(file);
> +	if (ret)
> +		return ret;
> +
> +flush:
> +	return blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
> +}
> +
> +static vm_fault_t zonefs_filemap_fault(struct vm_fault *vmf)
> +{
> +	struct zonefs_inode_info *zi = ZONEFS_I(file_inode(vmf->vma->vm_file));
> +	vm_fault_t ret;
> +
> +	down_read(&zi->i_mmap_sem);
> +	ret = filemap_fault(vmf);
> +	up_read(&zi->i_mmap_sem);
> +
> +	return ret;
> +}
> +
> +static vm_fault_t zonefs_filemap_page_mkwrite(struct vm_fault *vmf)
> +{
> +	struct inode *inode = file_inode(vmf->vma->vm_file);
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	vm_fault_t ret;
> +
> +	sb_start_pagefault(inode->i_sb);
> +	file_update_time(vmf->vma->vm_file);
> +
> +	/* Serialize against truncates */
> +	down_read(&zi->i_mmap_sem);
> +	ret = iomap_page_mkwrite(vmf, &zonefs_iomap_ops);
> +	up_read(&zi->i_mmap_sem);
> +
> +	sb_end_pagefault(inode->i_sb);
> +	return ret;
> +}
> +
> +static const struct vm_operations_struct zonefs_file_vm_ops = {
> +	.fault		= zonefs_filemap_fault,
> +	.map_pages	= filemap_map_pages,
> +	.page_mkwrite	= zonefs_filemap_page_mkwrite,
> +};
> +
> +static int zonefs_file_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> +	/*
> +	 * Conventional zone files can be mmap-ed READ/WRITE.
> +	 * For sequential zone files, only readonly mappings are possible.
> +	 */
> +	if (zonefs_file_is_seq(file_inode(file)) &&
> +	    (vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE))
> +		return -EINVAL;
> +
> +	file_accessed(file);
> +	vma->vm_ops = &zonefs_file_vm_ops;
> +
> +	return 0;
> +}
> +
> +static loff_t zonefs_file_llseek(struct file *file, loff_t offset, int whence)
> +{
> +	loff_t isize = i_size_read(file_inode(file));
> +
> +	/*
> +	 * Seeks are limited to below the zone size for conventional zones
> +	 * and below the zone write pointer for sequential zones. In both
> +	 * cases, this limit is the inode size.
> +	 */
> +	return generic_file_llseek_size(file, offset, whence, isize, isize);
> +}
> +
> +static ssize_t zonefs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(inode->i_sb);
> +	loff_t max_pos = zonefs_file_max_size(inode);
> +	size_t count;
> +	ssize_t ret = 0;
> +
> +	/*
> +	 * Check that the read operation does not go beyond the maximum
> +	 * file size.
> +	 */
> +	if (iocb->ki_pos >= zonefs_file_max_size(inode))
> +		return -EFBIG;
> +
> +	/*
> +	 * For sequential zones, limit reads to written data.
> +	 */
> +	if (zonefs_file_is_seq(inode))
> +		max_pos = i_size_read(inode);
> +	if (iocb->ki_pos >= max_pos)
> +		return 0;
> +
> +	iov_iter_truncate(to, max_pos - iocb->ki_pos);
> +	count = iov_iter_count(to);
> +	if (!count)
> +		return 0;
> +
> +	/* Direct IO reads must be aligned to device physical sector size */
> +	if ((iocb->ki_flags & IOCB_DIRECT) &&
> +	    ((iocb->ki_pos | count) & sbi->s_blocksize_mask))
> +		return -EINVAL;
> +
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock_shared(inode))
> +			return -EAGAIN;
> +	} else {
> +		inode_lock_shared(inode);
> +	}
> +
> +	if (iocb->ki_flags & IOCB_DIRECT) {
> +		file_accessed(iocb->ki_filp);
> +		ret = iomap_dio_rw(iocb, to, &zonefs_iomap_ops, NULL);
> +	} else {
> +		ret = generic_file_read_iter(iocb, to);
> +	}
> +
> +	inode_unlock_shared(inode);
> +
> +	return ret;
> +}
> +
> +/*
> + * We got a write error: get the sequenial zone information from the device to
> + * figure out where the zone write pointer is and verify the inode size against
> + * it.
> + */
> +static int zonefs_write_failed(struct inode *inode, int error)
> +{
> +	struct super_block *sb = inode->i_sb;
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	sector_t sector = zi->i_addr >> SECTOR_SHIFT;
> +	unsigned int noio_flag;
> +	struct blk_zone zone;
> +	int n = 1, ret;
> +
> +	zonefs_warn(sb, "Updating inode zone %llu info\n", sector);
> +
> +	noio_flag = memalloc_noio_save();
> +	ret = blkdev_report_zones(sb->s_bdev, sector, &zone, &n);
> +	memalloc_noio_restore(noio_flag);
> +
> +	if (!n)
> +		ret = -EIO;
> +	if (ret) {
> +		zonefs_err(sb, "Get zone %llu report failed %d\n",
> +			   sector, ret);
> +		return ret;
> +	}
> +
> +	zi->i_wpoffset = (zone.wp - zone.start) << SECTOR_SHIFT;
> +	if (i_size_read(inode) != zi->i_wpoffset) {
> +		i_size_write(inode, zi->i_wpoffset);
> +		truncate_pagecache(inode, zi->i_wpoffset);
> +	}
> +
> +	return error;
> +}
> +
> +static int zonefs_update_size(struct inode *inode, loff_t new_pos)
> +{
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +
> +	zi->i_wpoffset = new_pos;
> +	if (new_pos > i_size_read(inode))
> +		i_size_write(inode, new_pos);
> +	return 0;
> +}
> +
> +static int zonefs_dio_seqwrite_end_io(struct kiocb *iocb, ssize_t size,
> +				      unsigned int flags)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +	int ret;
> +
> +	inode_lock(inode);
> +	if (size < 0)
> +		ret = zonefs_write_failed(inode, size);
> +	else
> +		ret = zonefs_update_size(inode, iocb->ki_pos + size);
> +	inode_unlock(inode);
> +	return ret;
> +}
> +
> +static ssize_t zonefs_file_dio_aio_write(struct kiocb *iocb,
> +					 struct iov_iter *from)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	size_t count;
> +
> +	/*
> +	 * The size of conventional zone files is fixed to the zone size.
> +	 * So only direct writes to sequential zones need adjusting the
> +	 * inode size on IO completion.
> +	 */
> +	if (zonefs_file_is_conv(inode))
> +		return iomap_dio_rw(iocb, from, &zonefs_iomap_ops, NULL);
> +
> +	/* Enforce append only sequential writes */
> +	count = iov_iter_count(from);
> +	if (iocb->ki_pos != zi->i_wpoffset) {
> +		zonefs_err(inode->i_sb,
> +			   "Unaligned write at %llu + %zu (wp %llu)\n",
> +			   iocb->ki_pos, count, zi->i_wpoffset);
> +		return -EINVAL;
> +	}
> +
> +	if (is_sync_kiocb(iocb)) {
> +		/*
> +		 * Don't use the end_io callback for synchronous iocbs,
> +		 * as we'd deadlock on i_rwsem.  Instead perform the same
> +		 * actions manually here.
> +		 */
> +		count = iomap_dio_rw(iocb, from, &zonefs_iomap_ops, NULL);
> +		if (count < 0)
> +			return zonefs_write_failed(inode, count);
> +		zonefs_update_size(inode, iocb->ki_pos);
> +		return count;
> +	}
> +
> +	return iomap_dio_rw(iocb, from, &zonefs_iomap_ops,
> +			    zonefs_dio_seqwrite_end_io);
> +}
> +
> +static ssize_t zonefs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(inode->i_sb);
> +	size_t count;
> +	ssize_t ret;
> +
> +	/*
> +	 * Check that the read operation does not go beyond the file
> +	 * zone boundary.
> +	 */
> +	if (iocb->ki_pos >= zonefs_file_max_size(inode))
> +		return -EFBIG;
> +	iov_iter_truncate(from, zonefs_file_max_size(inode) - iocb->ki_pos);
> +	count = iov_iter_count(from);
> +
> +	if (!count)
> +		return 0;
> +
> +	/*
> +	 * Direct IO writes are mandatory for sequential zones so that write IO
> +	 * order is preserved. The direct writes also must be aligned to
> +	 * device physical sector size.
> +	 */
> +	if (iocb->ki_flags & IOCB_DIRECT) {
> +		if ((iocb->ki_pos | count) & sbi->s_blocksize_mask)
> +			return -EINVAL;
> +	} else {
> +		if (zonefs_file_is_seq(inode))
> +			return -EOPNOTSUPP;
> +	}
> +
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock(inode))
> +			return -EAGAIN;
> +	} else {
> +		inode_lock(inode);
> +	}
> +
> +	ret = generic_write_checks(iocb, from);
> +	if (ret <= 0)
> +		goto out;
> +
> +	if (iocb->ki_flags & IOCB_DIRECT)
> +		ret = zonefs_file_dio_aio_write(iocb, from);
> +	else
> +		ret = iomap_file_buffered_write(iocb, from, &zonefs_iomap_ops);
> +
> +out:
> +	inode_unlock(inode);
> +
> +	if (ret > 0 && (!(iocb->ki_flags & IOCB_DIRECT))) {
> +		iocb->ki_pos += ret;
> +		ret = generic_write_sync(iocb, ret);
> +	}
> +
> +	return ret;
> +}
> +
> +static const struct file_operations zonefs_file_operations = {
> +	.open		= zonefs_file_open,
> +	.fsync		= zonefs_file_fsync,
> +	.mmap		= zonefs_file_mmap,
> +	.llseek		= zonefs_file_llseek,
> +	.read_iter	= zonefs_file_read_iter,
> +	.write_iter	= zonefs_file_write_iter,
> +	.splice_read	= generic_file_splice_read,
> +	.splice_write	= iter_file_splice_write,
> +	.iopoll		= iomap_dio_iopoll,
> +};
> +
> +
> +static struct kmem_cache *zonefs_inode_cachep;
> +
> +static struct inode *zonefs_alloc_inode(struct super_block *sb)
> +{
> +	struct zonefs_inode_info *zi;
> +
> +	zi = kmem_cache_alloc(zonefs_inode_cachep, GFP_KERNEL);
> +	if (!zi)
> +		return NULL;
> +
> +	init_rwsem(&zi->i_mmap_sem);
> +	inode_init_once(&zi->i_vnode);
> +
> +	return &zi->i_vnode;
> +}
> +
> +static void zonefs_destroy_cb(struct rcu_head *head)
> +{
> +	struct inode *inode = container_of(head, struct inode, i_rcu);
> +
> +	kmem_cache_free(zonefs_inode_cachep, ZONEFS_I(inode));
> +}
> +
> +static void zonefs_destroy_inode(struct inode *inode)
> +{
> +	call_rcu(&inode->i_rcu, zonefs_destroy_cb);
> +}
> +
> +static struct dentry *zonefs_create_inode(struct dentry *parent,
> +					  const char *name,
> +					  struct blk_zone *zone)
> +{
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(parent->d_sb);
> +	struct inode *dir = d_inode(parent);
> +	struct dentry *dentry;
> +	struct inode *inode;
> +
> +	dentry = d_alloc_name(parent, name);
> +	if (!dentry)
> +		return NULL;
> +
> +	inode = new_inode(parent->d_sb);
> +	if (!inode)
> +		goto out_dput;
> +
> +	inode->i_ino = get_next_ino();
> +	if (zone) {
> +		struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +
> +		/* Zone file */
> +		inode->i_mode = S_IFREG | sbi->s_perm;
> +		if (zonefs_zone_readonly(zone))
> +			inode->i_mode &= ~S_IWUGO;
> +		inode->i_uid = sbi->s_uid;
> +		inode->i_gid = sbi->s_gid;
> +		zi->i_ztype = zonefs_zone_type(zone);
> +		zi->i_addr = zone->start << SECTOR_SHIFT;
> +		zi->i_max_size = zone->len << SECTOR_SHIFT;
> +		inode->i_blocks = zone->len;
> +		if (zonefs_file_is_conv(inode))
> +			zi->i_wpoffset = zi->i_max_size;
> +		else
> +			zi->i_wpoffset =
> +				(zone->wp - zone->start) << SECTOR_SHIFT;
> +		inode->i_size = zi->i_wpoffset;
> +		inode->i_fop = &zonefs_file_operations;
> +		inode->i_op = &zonefs_file_inode_operations;
> +		inode->i_mapping->a_ops = &zonefs_file_aops;
> +		inode->i_mapping->a_ops = &zonefs_file_aops;
> +	} else {
> +		/* Zone group directory */
> +		inode_init_owner(inode, dir, S_IFDIR | 0555);
> +		inode->i_fop = &simple_dir_operations;
> +		inode->i_op = &simple_dir_inode_operations;
> +		set_nlink(inode, 2);
> +		inc_nlink(dir);
> +	}
> +	inode->i_ctime = inode->i_mtime = inode->i_atime = dir->i_ctime;
> +
> +	d_add(dentry, inode);
> +	d_inode(parent)->i_size += sizeof(struct dentry);
> +
> +	return dentry;
> +
> +out_dput:
> +	dput(dentry);
> +	return NULL;
> +}
> +
> +/*
> + * File system stat.
> + */
> +static int zonefs_statfs(struct dentry *dentry, struct kstatfs *buf)
> +{
> +	struct super_block *sb = dentry->d_sb;
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
> +	sector_t nr_sectors = sb->s_bdev->bd_part->nr_sects;
> +	enum zonefs_ztype t;
> +
> +	buf->f_type = ZONEFS_MAGIC;
> +	buf->f_bsize = dentry->d_sb->s_blocksize;
> +	buf->f_namelen = ZONEFS_NAME_MAX;
> +
> +	buf->f_blocks = nr_sectors >> (sb->s_blocksize_bits - SECTOR_SHIFT);
> +	buf->f_bfree = 0;
> +	buf->f_bavail = 0;
> +
> +	buf->f_files = sbi->s_nr_zones[ZONEFS_ZTYPE_ALL] - 1;
> +	for (t = ZONEFS_ZTYPE_ALL; t < ZONEFS_ZTYPE_MAX; t++) {
> +		if (sbi->s_nr_zones[t])
> +			buf->f_files++;
> +	}
> +	buf->f_ffree = 0;
> +
> +	/* buf->f_fsid = 0; uuid, see ext2 */
> +	buf->f_namelen = ZONEFS_NAME_MAX;
> +
> +	return 0;
> +}
> +
> +static const struct super_operations zonefs_sops = {
> +	.alloc_inode	= zonefs_alloc_inode,
> +	.destroy_inode	= zonefs_destroy_inode,
> +	.statfs		= zonefs_statfs,
> +};
> +
> +static char *zgroups_name[ZONEFS_ZTYPE_MAX] = {
> +	NULL,
> +	"cnv",
> +	"seq"
> +};
> +
> +/*
> + * Create a zone group and populate it with zone files.
> + */
> +static int zonefs_create_zgroup(struct super_block *sb, struct blk_zone *zones,
> +				enum zonefs_ztype type)
> +{
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
> +	struct blk_zone *zone, *next, *end;
> +	char name[ZONEFS_NAME_MAX];
> +	unsigned int nr_files = 0;
> +	struct dentry *dir;
> +
> +	/* If the group is empty, nothing to do */
> +	if (!sbi->s_nr_zones[type])
> +		return 0;
> +
> +	dir = zonefs_create_inode(sb->s_root, zgroups_name[type], NULL);
> +	if (!dir)
> +		return -ENOMEM;
> +
> +	/*
> +	 * Note: The first zone contains the super block: skip it.
> +	 */
> +	end = zones + sbi->s_nr_zones[ZONEFS_ZTYPE_ALL];
> +	for (zone = &zones[1]; zone < end; zone = next) {
> +
> +		next = zone + 1;
> +		if (zonefs_zone_type(zone) != type)
> +			continue;
> +
> +		/* Ignore offline zones */
> +		if (zonefs_zone_offline(zone))
> +			continue;
> +
> +		/*
> +		 * For conventional zones, contiguous zones can be aggregated
> +		 * together to form larger files.
> +		 * Note that this overwrites the length of the first zone of
> +		 * the set of contiguous zones aggregated together.
> +		 * Only zones with the same condition can be agreggated so that
> +		 * offline zones are excluded and readonly zones are aggregated
> +		 * together into a read only file.
> +		 */
> +		if (type == ZONEFS_ZTYPE_CNV &&
> +		    zonefs_has_feature(sbi, ZONEFS_F_AGRCNV)) {
> +			for (; next < end; next++) {
> +				if (zonefs_zone_type(next) != type ||
> +				    next->cond != zone->cond)
> +					break;
> +				zone->len += next->len;
> +			}
> +		}
> +
> +		if (zonefs_has_feature(sbi, ZONEFS_F_STARTSECT_NAME))
> +			/* Use zone start sector as file names */
> +			snprintf(name, ZONEFS_NAME_MAX - 1, "%llu",
> +				 zone->start);
> +		else
> +			/* Use file number as file names */
> +			snprintf(name, ZONEFS_NAME_MAX - 1, "%u", nr_files);
> +		nr_files++;
> +
> +		if (!zonefs_create_inode(dir, name, zone))
> +			return -ENOMEM;
> +	}
> +
> +	zonefs_info(sb, "Zone group %d (%s), %u zones -> %u file%s\n",
> +		    type, zgroups_name[type], sbi->s_nr_zones[type],
> +		    nr_files, nr_files > 1 ? "s" : "");
> +
> +	return 0;
> +}
> +
> +static struct blk_zone *zonefs_get_zone_info(struct super_block *sb)
> +{
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
> +	struct block_device *bdev = sb->s_bdev;
> +	sector_t nr_sectors = bdev->bd_part->nr_sects;
> +	unsigned int i, n, nr_zones = 0;
> +	struct blk_zone *zones, *zone;
> +	sector_t sector = 0;
> +	int ret;
> +
> +	sbi->s_blocksize_mask = sb->s_blocksize - 1;
> +	sbi->s_nr_zones[ZONEFS_ZTYPE_ALL] = blkdev_nr_zones(bdev);
> +	zones = kvcalloc(sbi->s_nr_zones[ZONEFS_ZTYPE_ALL],
> +			 sizeof(struct blk_zone), GFP_KERNEL);
> +	if (!zones)
> +		return ERR_PTR(-ENOMEM);
> +
> +	/* Get zones information */
> +	zone = zones;
> +	while (nr_zones < sbi->s_nr_zones[ZONEFS_ZTYPE_ALL] &&
> +	       sector < nr_sectors) {
> +
> +		n = sbi->s_nr_zones[ZONEFS_ZTYPE_ALL] - nr_zones;
> +		ret = blkdev_report_zones(bdev, sector, zone, &n);
> +		if (ret) {
> +			zonefs_err(sb, "Zone report failed %d\n", ret);
> +			goto err;
> +		}
> +		if (!n) {
> +			zonefs_err(sb, "No zones reported\n");
> +			ret = -EIO;
> +			goto err;
> +		}
> +
> +		for (i = 0; i < n; i++) {
> +			switch (zone->type) {
> +			case BLK_ZONE_TYPE_CONVENTIONAL:
> +				zone->wp = zone->start + zone->len;
> +				if (zone > zones)
> +					sbi->s_nr_zones[ZONEFS_ZTYPE_CNV]++;
> +				break;
> +			case BLK_ZONE_TYPE_SEQWRITE_REQ:
> +			case BLK_ZONE_TYPE_SEQWRITE_PREF:
> +				if (zone > zones)
> +					sbi->s_nr_zones[ZONEFS_ZTYPE_SEQ]++;
> +				break;
> +			default:
> +				zonefs_err(sb, "Unsupported zone type 0x%x\n",
> +					   zone->type);
> +				ret = -EIO;
> +				goto err;
> +			}
> +			sector += zone->len;
> +			zone++;
> +		}
> +
> +		nr_zones += n;
> +	}
> +
> +	if (sector < nr_sectors ||
> +	    nr_zones < sbi->s_nr_zones[ZONEFS_ZTYPE_ALL]) {
> +		zonefs_err(sb, "Incomplete zone report\n");
> +		ret = -EIO;
> +		goto err;
> +	}
> +
> +	return zones;
> +
> +err:
> +	kvfree(zones);
> +	return ERR_PTR(ret);
> +}
> +
> +/*
> + * Read super block information from the device.
> + */
> +static int zonefs_read_super(struct super_block *sb)
> +{
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
> +	struct zonefs_super *super;
> +	struct bio bio;
> +	struct bio_vec bio_vec;
> +	struct page *page;
> +	int ret;
> +
> +	page = alloc_page(GFP_KERNEL);
> +	if (!page)
> +		return -ENOMEM;
> +
> +	bio_init(&bio, &bio_vec, 1);
> +	bio.bi_iter.bi_sector = 0;
> +	bio_set_dev(&bio, sb->s_bdev);
> +	bio_set_op_attrs(&bio, REQ_OP_READ, 0);
> +	bio_add_page(&bio, page, PAGE_SIZE, 0);
> +
> +	ret = submit_bio_wait(&bio);
> +	if (ret)
> +		goto out;
> +
> +	ret = -EINVAL;
> +	super = page_address(page);
> +	if (le32_to_cpu(super->s_magic) != ZONEFS_MAGIC)
> +		goto out;
> +	if (le32_to_cpu(super->s_version) != ZONEFS_VERSION)
> +		goto out;
> +	sbi->s_features = le64_to_cpu(super->s_features);
> +	if (zonefs_has_feature(sbi, ZONEFS_F_UID)) {
> +		sbi->s_uid = make_kuid(current_user_ns(),
> +				       le32_to_cpu(super->s_uid));
> +		if (!uid_valid(sbi->s_uid))
> +			goto out;
> +	}
> +	if (zonefs_has_feature(sbi, ZONEFS_F_GID)) {
> +		sbi->s_gid = make_kgid(current_user_ns(),
> +				       le32_to_cpu(super->s_gid));
> +		if (!gid_valid(sbi->s_gid))
> +			goto out;
> +	}
> +	if (zonefs_has_feature(sbi, ZONEFS_F_PERM))
> +		sbi->s_perm = le32_to_cpu(super->s_perm);
> +
> +	ret = 0;
> +
> +out:
> +	__free_page(page);
> +
> +	return ret;
> +}
> +
> +/*
> + * Check that the device is zoned. If it is, get the list of zones and create
> + * sub-directories and files according to the device zone configuration.
> + */
> +static int zonefs_fill_super(struct super_block *sb, void *data, int silent)
> +{
> +	struct zonefs_sb_info *sbi;
> +	struct blk_zone *zones;
> +	struct inode *inode;
> +	enum zonefs_ztype t;
> +	int ret;
> +
> +	/* Check device type */
> +	if (!bdev_is_zoned(sb->s_bdev)) {
> +		zonefs_err(sb, "Not a zoned block device\n");
> +		return -EINVAL;
> +	}
> +
> +	/* Initialize super block information */
> +	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> +	if (!sbi)
> +		return -ENOMEM;
> +
> +	sb->s_fs_info = sbi;
> +	sb->s_magic = ZONEFS_MAGIC;
> +	sb->s_maxbytes = MAX_LFS_FILESIZE;
> +	sb_set_blocksize(sb, bdev_physical_block_size(sb->s_bdev));
> +	sb->s_op = &zonefs_sops;
> +	sb->s_time_gran	= 1;
> +
> +	/* Set defaults */
> +	sbi->s_uid = GLOBAL_ROOT_UID;
> +	sbi->s_gid = GLOBAL_ROOT_GID;
> +	sbi->s_perm = S_IRUSR | S_IWUSR | S_IRGRP; /* 0640 */
> +
> +	ret = zonefs_read_super(sb);
> +	if (ret)
> +		return ret;
> +
> +	zones = zonefs_get_zone_info(sb);
> +	if (IS_ERR(zones))
> +		return PTR_ERR(zones);
> +
> +	pr_info("zonefs: Mounting %s, %u zones",
> +		sb->s_id, sbi->s_nr_zones[ZONEFS_ZTYPE_ALL]);
> +
> +	/* Create root directory inode */
> +	ret = -ENOMEM;
> +	inode = new_inode(sb);
> +	if (!inode)
> +		goto out;
> +	inode->i_ino = get_next_ino();
> +	inode->i_mode = S_IFDIR | 0755;
> +	inode->i_ctime = inode->i_mtime = inode->i_atime = current_time(inode);
> +	inode->i_op = &simple_dir_inode_operations;
> +	inode->i_fop = &simple_dir_operations;
> +	inode->i_size = sizeof(struct dentry) * 2;
> +	set_nlink(inode, 2);
> +	sb->s_root = d_make_root(inode);
> +	if (!sb->s_root)
> +		goto out;
> +
> +	/* Create and populate zone groups */
> +	for (t = ZONEFS_ZTYPE_CNV; t < ZONEFS_ZTYPE_MAX; t++) {
> +		ret = zonefs_create_zgroup(sb, zones, t);
> +		if (ret)
> +			break;
> +	}
> +
> +out:
> +	kvfree(zones);
> +
> +	return ret;
> +}
> +
> +static struct dentry *zonefs_mount(struct file_system_type *fs_type,
> +				 int flags, const char *dev_name, void *data)
> +{
> +	return mount_bdev(fs_type, flags, dev_name, data, zonefs_fill_super);
> +}
> +
> +static void zonefs_kill_super(struct super_block *sb)
> +{
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
> +
> +	kfree(sbi);
> +	if (sb->s_root)
> +		d_genocide(sb->s_root);
> +	kill_block_super(sb);
> +}
> +
> +/*
> + * File system definition and registration.
> + */
> +static struct file_system_type zonefs_type = {
> +	.owner		= THIS_MODULE,
> +	.name		= "zonefs",
> +	.mount		= zonefs_mount,
> +	.kill_sb	= zonefs_kill_super,
> +	.fs_flags	= FS_REQUIRES_DEV,
> +};
> +
> +static int __init zonefs_init_inodecache(void)
> +{
> +	zonefs_inode_cachep = kmem_cache_create("zonefs_inode_cache",
> +			sizeof(struct zonefs_inode_info), 0,
> +			(SLAB_RECLAIM_ACCOUNT | SLAB_MEM_SPREAD | SLAB_ACCOUNT),
> +			NULL);
> +	if (zonefs_inode_cachep == NULL)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
> +static void zonefs_destroy_inodecache(void)
> +{
> +	/*
> +	 * Make sure all delayed rcu free inodes are flushed before we
> +	 * destroy the inode cache.
> +	 */
> +	rcu_barrier();
> +	kmem_cache_destroy(zonefs_inode_cachep);
> +}
> +
> +static int __init zonefs_init(void)
> +{
> +	int ret;
> +
> +	ret = zonefs_init_inodecache();
> +	if (ret)
> +		return ret;
> +
> +	ret = register_filesystem(&zonefs_type);
> +	if (ret) {
> +		zonefs_destroy_inodecache();
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static void __exit zonefs_exit(void)
> +{
> +	zonefs_destroy_inodecache();
> +	unregister_filesystem(&zonefs_type);
> +}
> +
> +MODULE_AUTHOR("Damien Le Moal");
> +MODULE_DESCRIPTION("Zone file system for zoned block devices");
> +MODULE_LICENSE("GPL");
> +module_init(zonefs_init);
> +module_exit(zonefs_exit);
> diff --git a/fs/zonefs/zonefs.h b/fs/zonefs/zonefs.h
> new file mode 100644
> index 000000000000..91a9081c0d77
> --- /dev/null
> +++ b/fs/zonefs/zonefs.h
> @@ -0,0 +1,190 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Simple zone file system for zoned block devices.
> + *
> + * Copyright (C) 2019 Western Digital Corporation or its affiliates.
> + */
> +#ifndef __ZONEFS_H__
> +#define __ZONEFS_H__
> +
> +#include <linux/fs.h>
> +#include <linux/magic.h>
> +
> +/*
> + * Maximum length of file names: this only needs to be large enough to fit
> + * the zone group directory names and a decimal value of the start sector of
> + * the zones for file names. 16 characterse is plenty.
> + */
> +#define ZONEFS_NAME_MAX		16
> +
> +/*
> + * Zone types: ZONEFS_ZTYPE_SEQWRITE is used for all sequential zone types
> + * defined in linux/blkzoned.h, that is, BLK_ZONE_TYPE_SEQWRITE_REQ and
> + * BLK_ZONE_TYPE_SEQWRITE_PREF.
> + */
> +enum zonefs_ztype {
> +	ZONEFS_ZTYPE_ALL = 0,
> +	ZONEFS_ZTYPE_CNV,
> +	ZONEFS_ZTYPE_SEQ,
> +	ZONEFS_ZTYPE_MAX,
> +};
> +
> +static inline enum zonefs_ztype zonefs_zone_type(struct blk_zone *zone)
> +{
> +	if (zone->type == BLK_ZONE_TYPE_CONVENTIONAL)
> +		return ZONEFS_ZTYPE_CNV;
> +	return ZONEFS_ZTYPE_SEQ;
> +}
> +
> +static inline bool zonefs_zone_offline(struct blk_zone *zone)
> +{
> +	return zone->cond == BLK_ZONE_COND_OFFLINE;
> +}
> +
> +static inline bool zonefs_zone_readonly(struct blk_zone *zone)
> +{
> +	return zone->cond == BLK_ZONE_COND_READONLY;
> +}
> +
> +/*
> + * Inode private data.
> + */
> +struct zonefs_inode_info {
> +	struct inode		i_vnode;
> +	enum zonefs_ztype	i_ztype;
> +	loff_t			i_addr;
> +	loff_t			i_wpoffset;
> +	loff_t			i_max_size;
> +	struct rw_semaphore	i_mmap_sem;
> +};
> +
> +static inline struct zonefs_inode_info *ZONEFS_I(struct inode *inode)
> +{
> +	return container_of(inode, struct zonefs_inode_info, i_vnode);
> +}
> +
> +static inline bool zonefs_file_is_conv(struct inode *inode)
> +{
> +	return ZONEFS_I(inode)->i_ztype == ZONEFS_ZTYPE_CNV;
> +}
> +
> +static inline bool zonefs_file_is_seq(struct inode *inode)
> +{
> +	return ZONEFS_I(inode)->i_ztype == ZONEFS_ZTYPE_SEQ;
> +}
> +
> +/*
> + * Address (byte offset) on disk of a file zone.
> + */
> +static inline loff_t zonefs_file_addr(struct inode *inode)
> +{
> +	return ZONEFS_I(inode)->i_addr;
> +}
> +
> +/*
> + * Maximum possible size of a file (i.e. the zone size).
> + */
> +static inline loff_t zonefs_file_max_size(struct inode *inode)
> +{
> +	return ZONEFS_I(inode)->i_max_size;
> +}
> +
> +/*
> + * On-disk super block (block 0).
> + */
> +struct zonefs_super {
> +
> +	/* Magic number */
> +	__le32		s_magic;		/*    4 */
> +
> +	/* Metadata version number */
> +	__le32		s_version;		/*    8 */
> +
> +	/* Features */
> +	__le64		s_features;		/*   16 */
> +
> +	/* 128-bit uuid */
> +	__u8		s_uuid[16];		/*   32 */
> +
> +	/* UID/GID to use for files */
> +	__le32		s_uid;			/*   36 */
> +	__le32		s_gid;			/*   40 */
> +
> +	/* File permissions */
> +	__le32		s_perm;			/*   44 */
> +
> +	/* Padding to 4K */
> +	__u8		s_reserved[4052];	/* 4096 */
> +
> +} __attribute__ ((packed));
> +
> +/*
> + * Metadata version.
> + */
> +#define ZONEFS_VERSION	1
> +
> +/*
> + * Feature flags.
> + */
> +enum zonefs_features {
> +	/*
> +	 * Use a zone start sector value as file name.
> +	 */
> +	ZONEFS_F_STARTSECT_NAME,
> +	/*
> +	 * Aggregate contiguous conventional zones into a single file.
> +	 */
> +	ZONEFS_F_AGRCNV,
> +	/*
> +	 * Use super block specified UID for files instead of default.
> +	 */
> +	ZONEFS_F_UID,
> +	/*
> +	 * Use super block specified GID for files instead of default.
> +	 */
> +	ZONEFS_F_GID,
> +	/*
> +	 * Use super block specified file permissions instead of default 640.
> +	 */
> +	ZONEFS_F_PERM,
> +};
> +
> +/*
> + * In-memory Super block information.
> + */
> +struct zonefs_sb_info {
> +	/*
> +	 * Mount options.
> +	 */
> +	unsigned long		s_mnt_opt;
> +	unsigned long long	s_features;
> +	kuid_t			s_uid;		/* File owner UID */
> +	kgid_t			s_gid;		/* File owner GID */
> +	umode_t			s_perm;		/* File permissions */
> +
> +	/*
> +	 * Device information.
> +	 */
> +	loff_t			s_blocksize_mask;
> +	unsigned int		s_nr_zones[ZONEFS_ZTYPE_MAX];
> +};
> +
> +static inline struct zonefs_sb_info *ZONEFS_SB(struct super_block *sb)
> +{
> +	return sb->s_fs_info;
> +}
> +
> +static inline bool zonefs_has_feature(struct zonefs_sb_info *sbi,
> +				      enum zonefs_features f)
> +{
> +	return sbi->s_features & (1ULL << f);
> +}
> +
> +#define zonefs_info(sb, format, args...)	\
> +	pr_info("zonefs (%s): " format, sb->s_id, ## args)
> +#define zonefs_err(sb, format, args...)	\
> +	pr_err("zonefs (%s) ERROR: " format, sb->s_id, ## args)
> +#define zonefs_warn(sb, format, args...)	\
> +	pr_warn("zonefs (%s) WARN: " format, sb->s_id, ## args)
> +
> +#endif
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index f8c00045d537..57b627429f41 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -86,6 +86,7 @@
>  #define NSFS_MAGIC		0x6e736673
>  #define BPF_FS_MAGIC		0xcafe4a11
>  #define AAFS_MAGIC		0x5a3c69f0
> +#define ZONEFS_MAGIC		0x5a4f4653
>  
>  /* Since UDF 2.01 is ISO 13346 based... */
>  #define UDF_SUPER_MAGIC		0x15013346