Re: [PATCH v2] f2fs: get rid of buffer_head use

[Chao Yu]

On 2024/6/7 21:33, Matthew Wilcox wrote:
> On Fri, Jun 07, 2024 at 06:18:29PM +0800, Chao Yu wrote:
> > @@ -1990,6 +1989,12 @@ static inline struct f2fs_super_block *F2FS_RAW_SUPER(struct f2fs_sb_info *sbi)
> >   	return (struct f2fs_super_block *)(sbi->raw_super);
> >   }
> >   
> > +static inline struct f2fs_super_block *F2FS_SUPER_BLOCK(struct folio *folio)
> > +{
> > +	return (struct f2fs_super_block *)(page_address(folio_page(folio, 0)) +
> > +							F2FS_SUPER_OFFSET);
> > +}
>
> This assumes that the superblock is in the first page of the folio.
> That's not necessarily guaranteed; let's say you have a 64KiB folio
> that covers the start of the bdev.

Oh, I missed to add large folio support in this version.

For the case: page size is 4KiB, and folio size is 64KiB,
read_mapping_folio(mapping, 0, NULL) and read_mapping_folio(mapping,
1, NULL) will return the same #0 folio, right?

> I don't quite know how to write this because f2fs defines its block size
> in terms of PAGE_SIZE, which just seems like nonsense to me.  If you
> format a filesystem on a 16KiB PAGE_SIZE machine and then try to mount
> it on a machine with a 4KiB PAGE_SIZE, it's going to go horribly wrong.

f2fs will check on-disk block size w/ PAGE_SIZE in sanity_check_raw_super()
as below:

	/* only support block_size equals to PAGE_SIZE */
	if (le32_to_cpu(raw_super->log_blocksize) != F2FS_BLKSIZE_BITS) {
		f2fs_info(sbi, "Invalid log_blocksize (%u), supports only %u",
			  le32_to_cpu(raw_super->log_blocksize),
			  F2FS_BLKSIZE_BITS);
		return -EFSCORRUPTED;
	}

> You'd need to pass in something that indicates whether you're trying to
> access the first or second superblock; there's no way to tell from the
> folio which one it is.
>
> > +static int __f2fs_commit_super(struct f2fs_sb_info *sbi, struct folio *folio,
> > +								bool update)
> >   {
> > -	lock_buffer(bh);
> > -	if (super)
> > -		memcpy(bh->b_data + F2FS_SUPER_OFFSET, super, sizeof(*super));
> > -	set_buffer_dirty(bh);
> > -	unlock_buffer(bh);
> > -
> > +	struct bio *bio;
> >   	/* it's rare case, we can do fua all the time */
> > -	return __sync_dirty_buffer(bh, REQ_SYNC | REQ_PREFLUSH | REQ_FUA);
> > +	blk_opf_t opf = REQ_OP_WRITE | REQ_SYNC | REQ_PREFLUSH | REQ_FUA;
> > +	int ret;
> > +
> > +	folio_lock(folio);
> > +	folio_wait_writeback(folio);
> > +	if (update)
> > +		memcpy(F2FS_SUPER_BLOCK(folio), F2FS_RAW_SUPER(sbi),
> > +					sizeof(struct f2fs_super_block));
> > +	folio_mark_dirty(folio);
> > +	folio_clear_dirty_for_io(folio);
> > +	folio_start_writeback(folio);
> > +	folio_unlock(folio);
> > +
> > +	bio = bio_alloc(sbi->sb->s_bdev, 1, opf, GFP_NOFS);
> > +
> > +	/* it doesn't need to set crypto context for superblock update */
> > +	bio->bi_iter.bi_sector = SECTOR_FROM_BLOCK(folio_index(folio));
> > +
> > +	if (!bio_add_folio(bio, folio, PAGE_SIZE, 0))
> > +		f2fs_bug_on(sbi, 1);
>
> Better make that folio_size(folio) to support bs>PS.

Looks better, will update.

Thanks,

>