On 23.05.24 03:42, Matthew Wilcox wrote: > On Tue, May 14, 2024 at 05:22:08PM +0200, Johannes Thumshirn wrote: >> From: Johannes Thumshirn <johannes.thumshirn@xxxxxxx> >> >> Move reading of the on-disk superblock from page to kmalloc()ed memory. > > No, this is wrong. > >> + super = kzalloc(ZONEFS_SUPER_SIZE, GFP_KERNEL); >> + if (!super) >> return -ENOMEM; >> >> + folio = virt_to_folio(super); > > This will stop working at some point. It'll return NULL once we get > to the memdesc future (because the memdesc will be a slab, not a folio). > >> bio_init(&bio, sb->s_bdev, &bio_vec, 1, REQ_OP_READ); >> bio.bi_iter.bi_sector = 0; >> - __bio_add_page(&bio, page, PAGE_SIZE, 0); >> + bio_add_folio_nofail(&bio, folio, ZONEFS_SUPER_SIZE, >> + offset_in_folio(folio, super)); > > It also doesn't solve the problem of trying to read 4KiB from a device > with 16KiB sectors. We'll have to fail the bio because there isn't > enough memory in the bio to store one block. > > I think the right way to handle this is to call read_mapping_folio(). > That will allocate a folio in the page cache for you (obeying the > minimum folio size). Then you can examine the contents. It should > actually remove code from zonefs. Don't forget to call folio_put() > when you're done with it (either at unmount or at the end of mount if > you copy what you need elsewhere). > Hmm but read mapping folio needs an inode for the address_space. Or does the block device inode work here?
