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Date:   Tue, 7 Jan 2020 15:12:04 -0800
From:   "Darrick J. Wong" <darrick.wong@oracle.com>
To:     Damien Le Moal <damien.lemoal@wdc.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Johannes Thumshirn <jth@kernel.org>,
        Naohiro Aota <naohiro.aota@wdc.com>,
        Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH v5 1/2] fs: New zonefs file system
Message-ID: <20200107231204.GE917713@magnolia>
References: <20200103023445.1352524-1-damien.lemoal@wdc.com>
 <20200103023445.1352524-2-damien.lemoal@wdc.com>
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On Fri, Jan 03, 2020 at 11:34:44AM +0900, Damien Le Moal wrote:
> zonefs is a very simple file system exposing each zone of a zoned block
> device as a file. Unlike a regular file system with zoned block device
> support (e.g. f2fs), zonefs does not hide the sequential write
> constraint of zoned block devices to the user. Files representing
> sequential write zones of the device must be written sequentially
> starting from the end of the file (append only writes).

<snip>

> +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.

"Shared writable mappings are only possible on conventional zones"?

Otherwise, this looks fine to me.
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

One more suggestion: Have you considered making it easier to identify a
zonefs filesystem by stamping a UUID and/or label into the superblock?
At some point you might want to send a patch to libblkid to detect
zonefs so that users can do things like:

# mount LABEL=my_first_smr_drive /mnt

--D

> +	 */
> +	if (ZONEFS_I(file_inode(file))->i_ztype == ZONEFS_ZTYPE_SEQ &&
> +	    (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);
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	loff_t max_pos;
> +	size_t count;
> +	ssize_t ret;
> +
> +	if (iocb->ki_pos >= zi->i_max_size)
> +		return 0;
> +
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!inode_trylock_shared(inode))
> +			return -EAGAIN;
> +	} else {
> +		inode_lock_shared(inode);
> +	}
> +
> +	mutex_lock(&zi->i_truncate_mutex);
> +
> +	/*
> +	 * Limit read operations to written data.
> +	 */
> +	max_pos = i_size_read(inode);
> +	if (iocb->ki_pos >= max_pos) {
> +		mutex_unlock(&zi->i_truncate_mutex);
> +		ret = 0;
> +		goto out;
> +	}
> +
> +	iov_iter_truncate(to, max_pos - iocb->ki_pos);
> +
> +	mutex_unlock(&zi->i_truncate_mutex);
> +
> +	count = iov_iter_count(to);
> +
> +	if (iocb->ki_flags & IOCB_DIRECT) {
> +		if ((iocb->ki_pos | count) & sbi->s_blocksize_mask) {
> +			ret = -EINVAL;
> +			goto out;
> +		}
> +		file_accessed(iocb->ki_filp);
> +		ret = iomap_dio_rw(iocb, to, &zonefs_iomap_ops, NULL,
> +				   is_sync_kiocb(iocb));
> +	} else {
> +		ret = generic_file_read_iter(iocb, to);
> +	}
> +
> +out:
> +	inode_unlock_shared(inode);
> +
> +	return ret;
> +}
> +
> +static int zonefs_report_zones_err_cb(struct blk_zone *zone, unsigned int idx,
> +				      void *data)
> +{
> +	struct inode *inode = data;
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	loff_t pos;
> +
> +	/*
> +	 * The condition of the zone may have change. Check it and adjust the
> +	 * inode information as needed, similarly to zonefs_init_file_inode().
> +	 */
> +	if (zone->cond == BLK_ZONE_COND_OFFLINE) {
> +		inode->i_flags |= S_IMMUTABLE;
> +		inode->i_mode &= ~0777;
> +		zone->wp = zone->start;
> +	} else if (zone->cond == BLK_ZONE_COND_READONLY) {
> +		inode->i_flags |= S_IMMUTABLE;
> +		inode->i_mode &= ~0222;
> +	}
> +
> +	pos = (zone->wp - zone->start) << SECTOR_SHIFT;
> +	zi->i_wpoffset = pos;
> +	if (i_size_read(inode) != pos) {
> +		zonefs_update_stats(inode, pos);
> +		i_size_write(inode, pos);
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * When a write error occurs in a sequential zone, the zone write pointer
> + * position must be refreshed to correct the file size and zonefs inode
> + * write pointer offset.
> + */
> +static int zonefs_seq_file_write_failed(struct inode *inode, int error)
> +{
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	struct super_block *sb = inode->i_sb;
> +	sector_t sector = zi->i_zsector;
> +	unsigned int nofs_flag;
> +	int ret;
> +
> +	zonefs_warn(sb, "Updating inode zone %llu info\n", sector);
> +
> +	/*
> +	 * blkdev_report_zones() uses GFP_KERNEL by default. Force execution as
> +	 * if GFP_NOFS was specified so that it will not end up recursing into
> +	 * the FS on memory allocation.
> +	 */
> +	nofs_flag = memalloc_nofs_save();
> +	ret = blkdev_report_zones(sb->s_bdev, sector, 1,
> +				  zonefs_report_zones_err_cb, inode);
> +	memalloc_nofs_restore(nofs_flag);
> +
> +	if (ret != 1) {
> +		if (!ret)
> +			ret = -EIO;
> +		zonefs_err(sb, "Get zone %llu report failed %d\n",
> +			   sector, ret);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static int zonefs_file_dio_write_end(struct kiocb *iocb, ssize_t size, int ret,
> +				     unsigned int flags)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Conventional zone file size is fixed to the zone size so there
> +	 * is no need to do anything.
> +	 */
> +	if (zi->i_ztype == ZONEFS_ZTYPE_CNV)
> +		return 0;
> +
> +	mutex_lock(&zi->i_truncate_mutex);
> +
> +	if (size < 0) {
> +		ret = zonefs_seq_file_write_failed(inode, size);
> +	} else if (i_size_read(inode) < iocb->ki_pos + size) {
> +		zonefs_update_stats(inode, iocb->ki_pos + size);
> +		i_size_write(inode, iocb->ki_pos + size);
> +	}
> +
> +	mutex_unlock(&zi->i_truncate_mutex);
> +
> +	return ret;
> +}
> +
> +static const struct iomap_dio_ops zonefs_dio_ops = {
> +	.end_io			= zonefs_file_dio_write_end,
> +};
> +
> +static ssize_t zonefs_file_dio_write(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);
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	size_t count;
> +	ssize_t ret;
> +
> +	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;
> +
> +	iov_iter_truncate(from, zi->i_max_size - iocb->ki_pos);
> +	count = iov_iter_count(from);
> +
> +	/*
> +	 * Direct writes must be aligned to the block size, that is, the device
> +	 * physical sector size, to avoid errors when writing sequential zones
> +	 * on 512e devices (512B logical sector, 4KB physical sectors).
> +	 */
> +	if ((iocb->ki_pos | count) & sbi->s_blocksize_mask) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	/*
> +	 * Enforce sequential writes (append only) in sequential zones.
> +	 */
> +	mutex_lock(&zi->i_truncate_mutex);
> +	if (zi->i_ztype == ZONEFS_ZTYPE_SEQ &&
> +	    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);
> +		mutex_unlock(&zi->i_truncate_mutex);
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +	mutex_unlock(&zi->i_truncate_mutex);
> +
> +	ret = iomap_dio_rw(iocb, from, &zonefs_iomap_ops, &zonefs_dio_ops,
> +			   is_sync_kiocb(iocb));
> +	if (zi->i_ztype == ZONEFS_ZTYPE_SEQ &&
> +	    (ret > 0 || ret == -EIOCBQUEUED)) {
> +		if (ret > 0)
> +			count = ret;
> +		mutex_lock(&zi->i_truncate_mutex);
> +		zi->i_wpoffset += count;
> +		mutex_unlock(&zi->i_truncate_mutex);
> +	}
> +
> +out:
> +	inode_unlock(inode);
> +
> +	return ret;
> +}
> +
> +static ssize_t zonefs_file_buffered_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;
> +	ssize_t ret;
> +
> +	/*
> +	 * Direct IO writes are mandatory for sequential zones so that the
> +	 * write IO order is preserved.
> +	 */
> +	if (zi->i_ztype == ZONEFS_ZTYPE_SEQ)
> +		return -EIO;
> +
> +	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;
> +
> +	iov_iter_truncate(from, zi->i_max_size - iocb->ki_pos);
> +	count = iov_iter_count(from);
> +
> +	ret = iomap_file_buffered_write(iocb, from, &zonefs_iomap_ops);
> +	if (ret > 0)
> +		iocb->ki_pos += ret;
> +
> +out:
> +	inode_unlock(inode);
> +	if (ret > 0)
> +		ret = generic_write_sync(iocb, ret);
> +
> +	return ret;
> +}
> +
> +static ssize_t zonefs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
> +{
> +	struct inode *inode = file_inode(iocb->ki_filp);
> +
> +	/*
> +	 * Check that the write operation does not go beyond the zone size.
> +	 */
> +	if (iocb->ki_pos >= ZONEFS_I(inode)->i_max_size)
> +		return -EFBIG;
> +
> +	if (iocb->ki_flags & IOCB_DIRECT)
> +		return zonefs_file_dio_write(iocb, from);
> +
> +	return zonefs_file_buffered_write(iocb, from);
> +}
> +
> +static const struct file_operations zonefs_file_operations = {
> +	.open		= generic_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;
> +
> +	inode_init_once(&zi->i_vnode);
> +	mutex_init(&zi->i_truncate_mutex);
> +	init_rwsem(&zi->i_mmap_sem);
> +
> +	return &zi->i_vnode;
> +}
> +
> +static void zonefs_free_inode(struct inode *inode)
> +{
> +	kmem_cache_free(zonefs_inode_cachep, ZONEFS_I(inode));
> +}
> +
> +/*
> + * 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);
> +	enum zonefs_ztype t;
> +	u64 fsid;
> +
> +	buf->f_type = ZONEFS_MAGIC;
> +	buf->f_bsize = sb->s_blocksize;
> +	buf->f_namelen = ZONEFS_NAME_MAX;
> +
> +	spin_lock(&sbi->s_lock);
> +
> +	buf->f_blocks = sbi->s_blocks;
> +	if (WARN_ON(sbi->s_used_blocks > sbi->s_blocks))
> +		buf->f_bfree = 0;
> +	else
> +		buf->f_bfree = buf->f_blocks - sbi->s_used_blocks;
> +	buf->f_bavail = buf->f_bfree;
> +
> +	for (t = 0; t < ZONEFS_ZTYPE_MAX; t++) {
> +		if (sbi->s_nr_files[t])
> +			buf->f_files += sbi->s_nr_files[t] + 1;
> +	}
> +	buf->f_ffree = 0;
> +
> +	spin_unlock(&sbi->s_lock);
> +
> +	fsid = le64_to_cpup((void *)sbi->s_uuid.b) ^
> +		le64_to_cpup((void *)sbi->s_uuid.b + sizeof(u64));
> +	buf->f_fsid.val[0] = (u32)fsid;
> +	buf->f_fsid.val[1] = (u32)(fsid >> 32);
> +
> +	return 0;
> +}
> +
> +static const struct super_operations zonefs_sops = {
> +	.alloc_inode	= zonefs_alloc_inode,
> +	.free_inode	= zonefs_free_inode,
> +	.statfs		= zonefs_statfs,
> +};
> +
> +static const struct inode_operations zonefs_dir_inode_operations = {
> +	.lookup		= simple_lookup,
> +	.setattr	= zonefs_inode_setattr,
> +};
> +
> +static void zonefs_init_dir_inode(struct inode *parent, struct inode *inode)
> +{
> +	inode_init_owner(inode, parent, S_IFDIR | 0555);
> +	inode->i_op = &zonefs_dir_inode_operations;
> +	inode->i_fop = &simple_dir_operations;
> +	set_nlink(inode, 2);
> +	inc_nlink(parent);
> +}
> +
> +static void zonefs_init_file_inode(struct inode *inode, struct blk_zone *zone)
> +{
> +	struct super_block *sb = inode->i_sb;
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
> +	struct zonefs_inode_info *zi = ZONEFS_I(inode);
> +	umode_t	perm = sbi->s_perm;
> +
> +	if (zone->cond == BLK_ZONE_COND_OFFLINE) {
> +		/*
> +		 * Dead zone: make the inode immutable, disable all accesses
> +		 * and set the file size to 0.
> +		 */
> +		inode->i_flags |= S_IMMUTABLE;
> +		zone->wp = zone->start;
> +		perm &= ~0777;
> +	} else if (zone->cond == BLK_ZONE_COND_READONLY) {
> +		/* Do not allow writes in read-only zones */
> +		inode->i_flags |= S_IMMUTABLE;
> +		perm &= ~0222;
> +	}
> +
> +	zi->i_ztype = zonefs_zone_type(zone);
> +	zi->i_zsector = zone->start;
> +	zi->i_max_size = min_t(loff_t, MAX_LFS_FILESIZE,
> +			       zone->len << SECTOR_SHIFT);
> +	if (zi->i_ztype == ZONEFS_ZTYPE_CNV)
> +		zi->i_wpoffset = zi->i_max_size;
> +	else
> +		zi->i_wpoffset = (zone->wp - zone->start) << SECTOR_SHIFT;
> +
> +	inode->i_mode = S_IFREG | perm;
> +	inode->i_uid = sbi->s_uid;
> +	inode->i_gid = sbi->s_gid;
> +	inode->i_size = zi->i_wpoffset;
> +	inode->i_blocks = zone->len;
> +
> +	inode->i_op = &zonefs_file_inode_operations;
> +	inode->i_fop = &zonefs_file_operations;
> +	inode->i_mapping->a_ops = &zonefs_file_aops;
> +
> +	sb->s_maxbytes = max(zi->i_max_size, sb->s_maxbytes);
> +	sbi->s_blocks += zi->i_max_size >> sb->s_blocksize_bits;
> +	sbi->s_used_blocks += zi->i_wpoffset >> sb->s_blocksize_bits;
> +}
> +
> +static struct dentry *zonefs_create_inode(struct dentry *parent,
> +					const char *name, struct blk_zone *zone)
> +{
> +	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;
> +
> +	inode->i_ino = get_next_ino();
> +	inode->i_ctime = inode->i_mtime = inode->i_atime = dir->i_ctime;
> +	if (zone)
> +		zonefs_init_file_inode(inode, zone);
> +	else
> +		zonefs_init_dir_inode(dir, inode);
> +	d_add(dentry, inode);
> +	dir->i_size++;
> +
> +	return dentry;
> +
> +out:
> +	dput(dentry);
> +
> +	return NULL;
> +}
> +
> +static char *zgroups_name[ZONEFS_ZTYPE_MAX] = { "cnv", "seq" };
> +
> +struct zonefs_zone_data {
> +	struct super_block *sb;
> +	unsigned int nr_zones[ZONEFS_ZTYPE_MAX];
> +	struct blk_zone *zones;
> +};
> +
> +/*
> + * Create a zone group and populate it with zone files.
> + */
> +static int zonefs_create_zgroup(struct zonefs_zone_data *zd,
> +				enum zonefs_ztype type)
> +{
> +	struct super_block *sb = zd->sb;
> +	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
> +	struct blk_zone *zone, *next, *end;
> +	char name[ZONEFS_NAME_MAX];
> +	struct dentry *dir;
> +	unsigned int n = 0;
> +
> +	/* If the group is empty, there is nothing to do */
> +	if (!zd->nr_zones[type])
> +		return 0;
> +
> +	dir = zonefs_create_inode(sb->s_root, zgroups_name[type], NULL);
> +	if (!dir)
> +		return -ENOMEM;
> +
> +	/*
> +	 * The first zone contains the super block: skip it.
> +	 */
> +	end = zd->zones + blkdev_nr_zones(sb->s_bdev->bd_disk);
> +	for (zone = &zd->zones[1]; zone < end; zone = next) {
> +
> +		next = zone + 1;
> +		if (zonefs_zone_type(zone) != type)
> +			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 &&
> +		    (sbi->s_features & ZONEFS_F_AGGRCNV)) {
> +			for (; next < end; next++) {
> +				if (zonefs_zone_type(next) != type ||
> +				    next->cond != zone->cond)
> +					break;
> +				zone->len += next->len;
> +			}
> +		}
> +
> +		/*
> +		 * Use the file number within its group as file name.
> +		 */
> +		snprintf(name, ZONEFS_NAME_MAX - 1, "%u", n);
> +		if (!zonefs_create_inode(dir, name, zone))
> +			return -ENOMEM;
> +
> +		n++;
> +	}
> +
> +	zonefs_info(sb, "Zone group \"%s\" has %u file%s\n",
> +		    zgroups_name[type], n, n > 1 ? "s" : "");
> +
> +	sbi->s_nr_files[type] = n;
> +
> +	return 0;
> +}
> +
> +static int zonefs_get_zone_info_cb(struct blk_zone *zone, unsigned int idx,
> +				   void *data)
> +{
> +	struct zonefs_zone_data *zd = data;
> +
> +	/*
> +	 * Count the number of usable zones: the first zone at index 0 contains
> +	 * the super block and is ignored.
> +	 */
> +	switch (zone->type) {
> +	case BLK_ZONE_TYPE_CONVENTIONAL:
> +		zone->wp = zone->start + zone->len;
> +		if (idx)
> +			zd->nr_zones[ZONEFS_ZTYPE_CNV]++;
> +		break;
> +	case BLK_ZONE_TYPE_SEQWRITE_REQ:
> +	case BLK_ZONE_TYPE_SEQWRITE_PREF:
> +		if (idx)
> +			zd->nr_zones[ZONEFS_ZTYPE_SEQ]++;
> +		break;
> +	default:
> +		zonefs_err(zd->sb, "Unsupported zone type 0x%x\n",
> +			   zone->type);
> +		return -EIO;
> +	}
> +
> +	memcpy(&zd->zones[idx], zone, sizeof(struct blk_zone));
> +
> +	return 0;
> +}
> +
> +static int zonefs_get_zone_info(struct zonefs_zone_data *zd)
> +{
> +	struct block_device *bdev = zd->sb->s_bdev;
> +	int ret;
> +
> +	zd->zones = kvcalloc(blkdev_nr_zones(bdev->bd_disk),
> +			     sizeof(struct blk_zone), GFP_KERNEL);
> +	if (!zd->zones)
> +		return -ENOMEM;
> +
> +	/* Get zones information */
> +	ret = blkdev_report_zones(bdev, 0, BLK_ALL_ZONES,
> +				  zonefs_get_zone_info_cb, zd);
> +	if (ret < 0) {
> +		zonefs_err(zd->sb, "Zone report failed %d\n", ret);
> +		return ret;
> +	}
> +
> +	if (ret != blkdev_nr_zones(bdev->bd_disk)) {
> +		zonefs_err(zd->sb, "Invalid zone report (%d/%u zones)\n",
> +			   ret, blkdev_nr_zones(bdev->bd_disk));
> +		return -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +static inline void zonefs_cleanup_zone_info(struct zonefs_zone_data *zd)
> +{
> +	kvfree(zd->zones);
> +}
> +
> +/*
> + * 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;
> +	u32 crc, stored_crc;
> +	struct page *page;
> +	struct bio_vec bio_vec;
> +	struct bio bio;
> +	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;
> +
> +	super = page_address(page);
> +
> +	stored_crc = le32_to_cpu(super->s_crc);
> +	super->s_crc = 0;
> +	crc = crc32(~0U, (unsigned char *)super, sizeof(struct zonefs_super));
> +	if (crc != stored_crc) {
> +		zonefs_err(sb, "Invalid checksum (Expected 0x%08x, got 0x%08x)",
> +			   crc, stored_crc);
> +		ret = -EIO;
> +		goto out;
> +	}
> +
> +	ret = -EINVAL;
> +	if (le32_to_cpu(super->s_magic) != ZONEFS_MAGIC)
> +		goto out;
> +
> +	sbi->s_features = le64_to_cpu(super->s_features);
> +	if (sbi->s_features & ~ZONEFS_F_DEFINED_FEATURES) {
> +		zonefs_err(sb, "Unknown features set 0x%llx\n",
> +			   sbi->s_features);
> +		goto out;
> +	}
> +
> +	if (sbi->s_features & ZONEFS_F_UID) {
> +		sbi->s_uid = make_kuid(current_user_ns(),
> +				       le32_to_cpu(super->s_uid));
> +		if (!uid_valid(sbi->s_uid)) {
> +			zonefs_err(sb, "Invalid UID feature\n");
> +			goto out;
> +		}
> +	}
> +
> +	if (sbi->s_features & ZONEFS_F_GID) {
> +		sbi->s_gid = make_kgid(current_user_ns(),
> +				       le32_to_cpu(super->s_gid));
> +		if (!gid_valid(sbi->s_gid)) {
> +			zonefs_err(sb, "Invalid GID feature\n");
> +			goto out;
> +		}
> +	}
> +
> +	if (sbi->s_features & ZONEFS_F_PERM)
> +		sbi->s_perm = le32_to_cpu(super->s_perm);
> +
> +	if (memchr_inv(super->s_reserved, 0, sizeof(super->s_reserved))) {
> +		zonefs_err(sb, "Reserved area is being used\n");
> +		goto out;
> +	}
> +
> +	uuid_copy(&sbi->s_uuid, &super->s_uuid);
> +	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 and
> + * format options.
> + */
> +static int zonefs_fill_super(struct super_block *sb, void *data, int silent)
> +{
> +	struct zonefs_zone_data zd;
> +	struct zonefs_sb_info *sbi;
> +	struct inode *inode;
> +	enum zonefs_ztype t;
> +	int ret;
> +
> +	if (!bdev_is_zoned(sb->s_bdev)) {
> +		zonefs_err(sb, "Not a zoned block device\n");
> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * Initialize super block information: the maximum file size is updated
> +	 * when the zone files are created so that the format option
> +	 * ZONEFS_F_AGGRCNV which increases the maximum file size of a file
> +	 * beyond the zone size is taken into account.
> +	 */
> +	sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> +	if (!sbi)
> +		return -ENOMEM;
> +
> +	spin_lock_init(&sbi->s_lock);
> +	sb->s_fs_info = sbi;
> +	sb->s_magic = ZONEFS_MAGIC;
> +	sb->s_maxbytes = 0;
> +	sb->s_op = &zonefs_sops;
> +	sb->s_time_gran	= 1;
> +
> +	/*
> +	 * The block size is always equal to the device physical sector size to
> +	 * ensure that writes on 512e devices (512B logical block and 4KB
> +	 * physical block) are always aligned to the device physical blocks
> +	 * (as required for writes to sequential zones on ZBC/ZAC disks).
> +	 */
> +	sb_set_blocksize(sb, bdev_physical_block_size(sb->s_bdev));
> +	sbi->s_blocksize_mask = sb->s_blocksize - 1;
> +	sbi->s_uid = GLOBAL_ROOT_UID;
> +	sbi->s_gid = GLOBAL_ROOT_GID;
> +	sbi->s_perm = 0640;
> +
> +	ret = zonefs_read_super(sb);
> +	if (ret)
> +		return ret;
> +
> +	memset(&zd, 0, sizeof(struct zonefs_zone_data));
> +	zd.sb = sb;
> +	ret = zonefs_get_zone_info(&zd);
> +	if (ret)
> +		goto out;
> +
> +	zonefs_info(sb, "Mounting %u zones",
> +		    blkdev_nr_zones(sb->s_bdev->bd_disk));
> +
> +	/* 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 | 0555;
> +	inode->i_ctime = inode->i_mtime = inode->i_atime = current_time(inode);
> +	inode->i_op = &zonefs_dir_inode_operations;
> +	inode->i_fop = &simple_dir_operations;
> +	set_nlink(inode, 2);
> +
> +	sb->s_root = d_make_root(inode);
> +	if (!sb->s_root)
> +		goto out;
> +
> +	/* Create and populate files in zone groups directories */
> +	for (t = 0; t < ZONEFS_ZTYPE_MAX; t++) {
> +		ret = zonefs_create_zgroup(&zd, t);
> +		if (ret)
> +			break;
> +	}
> +
> +out:
> +	zonefs_cleanup_zone_info(&zd);
> +
> +	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;
> +
> +	BUILD_BUG_ON(sizeof(struct zonefs_super) != ZONEFS_SUPER_SIZE);
> +
> +	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..0296b3426f7b
> --- /dev/null
> +++ b/fs/zonefs/zonefs.h
> @@ -0,0 +1,169 @@
> +/* 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>
> +#include <linux/uuid.h>
> +#include <linux/mutex.h>
> +#include <linux/rwsem.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 characters is plenty.
> + */
> +#define ZONEFS_NAME_MAX		16
> +
> +/*
> + * Zone types: ZONEFS_ZTYPE_SEQ 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_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;
> +}
> +
> +/*
> + * In-memory inode data.
> + */
> +struct zonefs_inode_info {
> +	struct inode		i_vnode;
> +
> +	/* File zone type */
> +	enum zonefs_ztype	i_ztype;
> +
> +	/* File zone start sector (512B unit) */
> +	sector_t		i_zsector;
> +
> +	/* File zone write pointer position (sequential zones only) */
> +	loff_t			i_wpoffset;
> +
> +	/* File maximum size */
> +	loff_t			i_max_size;
> +
> +	/*
> +	 * To serialise fully against both syscall and mmap based IO and
> +	 * sequential file truncation, two locks are used. For serializing
> +	 * zonefs_seq_file_truncate() against zonefs_iomap_begin(), that is,
> +	 * file truncate operations against block mapping, i_truncate_mutex is
> +	 * used. i_truncate_mutex also protects against concurrent accesses
> +	 * and changes to the inode private data, and in particular changes to
> +	 * a sequential file size on completion of direct IO writes.
> +	 * Serialization of mmap read IOs with truncate and syscall IO
> +	 * operations is done with i_mmap_sem in addition to i_truncate_mutex.
> +	 * Only zonefs_seq_file_truncate() takes both lock (i_mmap_sem first,
> +	 * i_truncate_mutex second).
> +	 */
> +	struct mutex		i_truncate_mutex;
> +	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);
> +}
> +
> +/*
> + * On-disk super block (block 0).
> + */
> +#define ZONEFS_SUPER_SIZE	4096
> +struct zonefs_super {
> +
> +	/* Magic number */
> +	__le32		s_magic;
> +
> +	/* Checksum */
> +	__le32		s_crc;
> +
> +	/* Features */
> +	__le64		s_features;
> +
> +	/* 128-bit uuid */
> +	uuid_t		s_uuid;
> +
> +	/* UID/GID to use for files */
> +	__le32		s_uid;
> +	__le32		s_gid;
> +
> +	/* File permissions */
> +	__le32		s_perm;
> +
> +	/* Padding to ZONEFS_SUPER_SIZE bytes */
> +	__u8		s_reserved[4052];
> +
> +} __packed;
> +
> +/*
> + * Feature flags: used on disk in the s_features field of struct zonefs_super
> + * and in-memory in the s_feartures field of struct zonefs_sb_info.
> + */
> +enum zonefs_features {
> +	/*
> +	 * Aggregate contiguous conventional zones into a single file.
> +	 */
> +	ZONEFS_F_AGGRCNV = 1ULL << 0,
> +	/*
> +	 * Use super block specified UID for files instead of default.
> +	 */
> +	ZONEFS_F_UID = 1ULL << 1,
> +	/*
> +	 * Use super block specified GID for files instead of default.
> +	 */
> +	ZONEFS_F_GID = 1ULL << 2,
> +	/*
> +	 * Use super block specified file permissions instead of default 640.
> +	 */
> +	ZONEFS_F_PERM = 1ULL << 3,
> +};
> +
> +#define ZONEFS_F_DEFINED_FEATURES \
> +	(ZONEFS_F_AGGRCNV | ZONEFS_F_UID | ZONEFS_F_GID | ZONEFS_F_PERM)
> +
> +/*
> + * In-memory Super block information.
> + */
> +struct zonefs_sb_info {
> +
> +	spinlock_t		s_lock;
> +
> +	unsigned long long	s_features;
> +	kuid_t			s_uid;
> +	kgid_t			s_gid;
> +	umode_t			s_perm;
> +	uuid_t			s_uuid;
> +	loff_t			s_blocksize_mask;
> +
> +	unsigned int		s_nr_files[ZONEFS_ZTYPE_MAX];
> +
> +	loff_t			s_blocks;
> +	loff_t			s_used_blocks;
> +};
> +
> +static inline struct zonefs_sb_info *ZONEFS_SB(struct super_block *sb)
> +{
> +	return sb->s_fs_info;
> +}
> +
> +#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 3ac436376d79..d78064007b17 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -87,6 +87,7 @@
>  #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
> -- 
> 2.24.1
>