On Thu, Nov 22, 2018 at 07:24:17AM +0300, Alexey Lyashkov wrote: > 1024 is jbd superblock size, and this constant widely used over e2fsprogs code. > from this particular case it’s clear bug as jsb_buffer defined as. > >> > char jsb_buffer[1024]; The jbd superblock size is 1024 bytes --- just as the ext4 superblock is only 1024 bytes. It may be *stored* in a 4k block, and the size of the super block has nothingm to do with the size of the file system block size. It gets used here: if (exp_block_size != (int) ntohl(jsb->s_blocksize)) fprintf(f, "Journal block size: %u\n", (unsigned int)ntohl(jsb->s_blocksize)); The normal case is when the journal superblock size is the same as the file system block size, and in that case, there's no reason to print the journal block size. It *can* happen where the journal block size can be different from the file system block size. The most likely case is the one where an external journal is in use, and the external journal is shared between two file systems, one which uses (say) a 4k block size, and the other uses (say) a 1k block size. The data structures support this mode, but what we don't have is e2fsck support for handling a journal replay where the journal needs to be replayed to two different file systems --- especially if one of the block device is temporarily unavailable. So that's why this is there, and in fact it's intentional that it's done this way. Cheers, - Ted
