On Tue, Jul 20, 2021 at 01:42:24PM -0700, Darrick J. Wong wrote: > > - BUG_ON(page_has_private(page)); > > - BUG_ON(page->index); > > - BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data)); > > + /* inline source data must be inside a single page */ > > + BUG_ON(iomap->length > PAGE_SIZE - offset_in_page(iomap->inline_data)); > > Can we reduce the strength of these checks to a warning and an -EIO > return? I'm not entirely sure that we need this check, tbh. > > + /* handle tail-packing blocks cross the current page into the next */ > > + size = min_t(unsigned int, iomap->length + pos - iomap->offset, > > + PAGE_SIZE - poff); > > > > addr = kmap_atomic(page); > > - memcpy(addr, iomap->inline_data, size); > > - memset(addr + size, 0, PAGE_SIZE - size); > > + memcpy(addr + poff, iomap->inline_data - iomap->offset + pos, size); > > + memset(addr + poff + size, 0, PAGE_SIZE - poff - size); > > Hmm, so I guess the point of this is to support reading data from a > tail-packing block, where each file gets some arbitrary byte range > within the tp-block, and the range isn't aligned to an fs block? Hence > you have to use the inline data code to read the relevant bytes and copy > them into the pagecache? I think there are two distinct cases for IOMAP_INLINE. One is where the tail of the file is literally embedded into the inode. Like ext4 fast symbolic links. Taking the ext4 i_blocks layout as an example, you could have a 4kB block stored in i_block[0] and then store bytes 4096-4151 in i_block[1-14] (although reading https://www.kernel.org/doc/html/latest/filesystems/ext4/dynamic.html makes me think that ext4 only supports storing 0-59 in the i_blocks; it doesn't support 0-4095 in i_block[0] and then 4096-4151 in i_blocks) The other is what I think erofs is doing where, for example, you'd specify in i_block[1] the block which contains the tail and then in i_block[2] what offset of the block the tail starts at.
