I am just adding references here to tie in the previous discussions. The bugzilla.redhat.com discussion actually has the best analysis of the problem. However let me summarize (and plagarize) as best as I can here.
In https://bugzilla.redhat.com/show_bug.cgi?id=485507 Eric Sandeen proposed to add ext4 to the list of names currently reported for that type of file system ("ext2/ext3"). In response Jim stated: http://lists.gnu.org/archive/html/bug-coreutils/2009-02/msg00160.html I'm reluctant to change that string, because doing so might well break scripts that rely on them: case $(stat -f --format %T .) in ext2/ext3) ;; *) destroy_partition ;; esac Sure, script writers might well anticipate this and prefer to use the %t directive to get the type in hexadecimal, but that's far less readable. How much code (and how ugly) would be required to distinguish ext4 from ext[23]? This was further reinforced by Jim in a later discussion: http://lists.gnu.org/archive/html/bug-coreutils/2009-12/msg00229.html For the ext4-adding part, I'm a little reluctant, because it may break scripts that test via e.g., test "$(stat -f -c %T .)" = ext2/ext3 && ... rather than the more portable -- in potential retrospect: case $(stat -f -c %T .) in ext2/ext3*) ... ; esac In the previous thread Eric suggested some pseudo-code flow to distinguish ext4 from ext* but it would have needed significant effort to complete. This was followed up in the in the bugzilla trail especially this where we see that the problem of distinguishing ext4 is not trivial and opens a box of problems. I think it is worthwhile to share it here. https://bugzilla.redhat.com/show_bug.cgi?id=485507#c7 Eric Sandeen 2012-04-25 17:05:14 EDT A big part of the problem is that "ext4" is a big, random collection of features. It's more a new driver codebase containing various & sundry new things, than a fixed on-disk format. You can turn any/all of the following on or off and mount it with the ext4 driver: * extents * delalloc * flex_bg * journaling * 64-bitness * "bigalloc" * .... etc .... So the question becomes, what exactly _is_ ext4? Best we can do is "ext2/3/4" or so, I think. https://bugzilla.redhat.com/show_bug.cgi?id=485507#c8 Ondrej Vasik 2012-04-25 19:33:20 EDT But upstream (Jim Meyering) already rejected ext2/3/4 change - as it may break scripts - and recognizing ext4 based on some feature might be a tricky thing - as Eric mentioned - and will polute the stat code. Bad luck that ext2/3/4 uses the same magic for all filesystems. https://bugzilla.redhat.com/show_bug.cgi?id=485507#c9 Eric Sandeen 2012-04-25 20:08:06 EDT Best to close it WONTFIX then, I guess? https://bugzilla.redhat.com/show_bug.cgi?id=485507#c10 Ondrej Vasik 2012-04-26 02:06:03 EDT Probably... closing WONTFIX, anyone - feel free to reopen it if you find an easy way how to reliably distinguish ext2/3 and ext4 filesystem (or just propose it as reply in upstream thread mentioned in comment #4 or #5 - as this possible change has to be done/accepted upstream). These ways I'm aware of are too big for stat.c code. I think the above rationale is still a good place to start. It is unfortunate that ext4 is using the same identifier as ext3. And the same that ext3 used the same identifier as ext2. Bob
