Re: [PATCH V3] fs: New zonefs file system

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2019/08/21 23:59, Darrick J. Wong wrote:
> On Wed, Aug 21, 2019 at 04:03:08PM +0900, Damien Le Moal wrote:
>> zonefs is a very simple file system exposing each zone of a zoned
>> block device as a file. zonefs is in fact closer to a raw block device
>> access interface than to a full feature POSIX file system.
> 
> <skipping to the good part>
> 
>> +/*
>> + * Read super block information from the device.
>> + */
>> +static int zonefs_read_super(struct super_block *sb)
>> +{
>> +	const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
>> +	struct zonefs_sb_info *sbi = ZONEFS_SB(sb);
>> +	struct zonefs_super *super;
>> +	struct bio bio;
>> +	struct bio_vec bio_vec;
>> +	struct page *page;
>> +	u32 crc, stored_crc;
>> +	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 = super->s_crc;
>> +	super->s_crc = 0;
>> +	crc = crc32_le(ZONEFS_MAGIC, (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 & ~((1ULL << ZONEFS_F_NUM) - 1)) {
> 
> Most other filesystems would do:
> 
> #define ZONEFS_F_ALL_FEATURES (ZONEFS_F_UID | ZONEFS_F_GID ...)
> 
> and then this becomes:
> 
> if (sbi->s_features & ~ZONEFS_F_ALL_FEATURES)

OK. Will do that.

>> +		zonefs_err(sb, "Unknown features set\n");
> 
> Also it might help to print out the invalid s_features values so that
> when you get help questions you can distinguish between a corrupted
> superblock and a new fs on an old kernel.

Good point. Will add that.

> 
>> +		goto out;
>> +	}
>> +
>> +
>> +	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)) {
>> +			zonefs_err(sb, "Invalid UID feature\n");
>> +			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)) {
>> +			zonefs_err(sb, "Invalid GID feature\n");
>> +			goto out;
>> +		}
>> +	}
>> +
>> +	if (zonefs_has_feature(sbi, ZONEFS_F_PERM))
>> +		sbi->s_perm = le32_to_cpu(super->s_perm);
>> +
>> +	if (memcmp(super->s_reserved, zero_page, sizeof(super->s_reserved))) {
> 
> Er... memchr_inv?

Ah. Yes. Good idea. That will avoid the need for using zero page.

> 
> Otherwise looks reasonable enough.  How do you test zonedfs?

I created a small test suite that I put together with zonefs-tools in the github
repo (see https://github.com/damien-lemoal/zonefs-tools). The tests run against
real devices, DM devices (dm-linear chunks of a larger device) and null_blk
devices with memory backing and zoned mode enabled (there is a script for
running against this one automatically).

This test suite is still small-ish but improving. For now, I have tests for
checking number of files created and their attributes, truncate and unlink, and
IO paths (read and write, sync and async) using dd and fio. I need to add some
more test cases for mmap at least (tested "manually" for now). I will eventually
need to go through xfstests to see what generic test cases can apply. Not many I
guess given the limited features of zonefs. Will see.

Best regards.


-- 
Damien Le Moal
Western Digital Research