On Wed, Aug 11, 2021 at 04:32:53PM -0700, Darrick J. Wong wrote: > +/* > + * Returns true if the user is forcing an old format (e.g. ext2, ext3). > + * > + * If there is no fs_types list, the user invoked us with no explicit type and > + * gets the default (ext4) format. If we find the latest format (ext4) in the > + * type list, some combination of program name and -T argument put us in ext4 > + * mode. Anything else (ext2, ext3, hurd) and we return false. > + */ So that's not actually quite right. Even if the user has no explicit type, mke2fs will assign a default type --- and it's not necessarily ext4. You can see what the contents of the fs_types list using the -v option: % /bin/rm /tmp/foo.img ; mke2fs -vq /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext2', 'small' % /bin/rm /tmp/foo.img ; mke2fs -vq -T news /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext2', 'news' % /bin/rm /tmp/foo.img ; mkfs.ext4 -vq /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext4', 'small' % /bin/rm /tmp/foo.img ; mkfs.ext4 -T huge -vq /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext4', 'huge' % /bin/rm /tmp/foo.img ; mkfs.ext4 -o hurd -vq /tmp/foo.img 8m fs_types for mke2fs.conf resolution: 'ext2', 'small', 'hurd' Also note that the ext2/ext3/ext4 fs_type will always be in fs_types[0], so it's not necessary to search the entire list, as the patch is currently doing: > + for (i = 0; fs_types[i]; i++) > + if (!strcmp(fs_types[i], "ext4")) > + found_ext4 = 1; Cheers, - Ted P.S. Although I'm not aware of anyone actually doing this, if there mke2fs is installed as mke3fs or mke4fs, that's the equivalent of mkfs.ext3 and mkfs.ext4. (See the logic in the parse_fs_type function.) Although perhaps there is some obscure distro somewhere out there that I don't know about....
