On Mon, Jul 01, 2019 at 05:53:34PM -0700, James Bottomley wrote: > > Actually, we control the location of the IPL, so as long as mke2fs > errors out if we get it wrong I can add an offset so it begins at > sector 258. Palo actually executed mke2fs when you initialize the > partition so it can add any options it likes. I was also thinking I > should update palo to support ext4 as well. If you never going to resize the boot partition, because it's fixed size, you might as we not waste space on the reserving blocks for online resize. So having the palo bootloader be very restrictive about what features it enables probably makes sense. > Well, we don't have to use badblocks to achieve this, but we would like > a way to make an inode cover the reserved physical area of the IPL. > Effectively it's a single contiguous area on disk with specific > absolute alignment constraints. It doesn't actually matter if it > appears in the directory tree. If you don't mind that it is visible in the namespace, you could take advantage of the existing mk_hugefile feature[1][2] [1] http://man7.org/linux/man-pages/man5/mke2fs.conf.5.html [2] https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git/tree/misc/mk_hugefiles.c # cat >> /etc/mke2fs.conf < EOF [fs_types] palo_boot = { features = ^resize_inode blocksize = 1024 make_hugefiles = true num_hugefiles = 1 hugefiles_dir = /palo hugefiles_name = IPL hugefiles_size = 214k hugefiles_align = 256k hugefiles_align_disk = true } EOF # mke2fs -T palo_boot /dev/sda1 Something like this will create a 1k block file system, containing a zero-filled /palo/IPL which is 214k long, aligned with respect to the beginning of the disk at an 256k boundary. (This feature was sponsored by the letters, 'S', 'M', and 'R'. :-) If you wanted it to be hidden from the file system you could just drop the hugefiles_dir line above, and then after mounting the file system run open the /IPL file and then execute the EXT4_IOC_SWAP_BOOT ioctl on it. This will move those blocks so they are owned by inode #5, an inode reserved for the boot loader. Cheers, - Ted
