How to detect whether the filesystem is ext2 or ext3??

fa3a · 01-14-2004, 08:01 AM

The matter is that the magic number for ext2 fs is the same as for ext3 fs. So how is it possible to detect whether the fyle system is type of ext2 or ext3 in the C/C++ program??

UltimaGuy · 01-21-2004, 07:05 AM

The file system is the same. the only thing that changes is that you have journaling in ext3. Try to find out whether journaling is present or not, and you have the file system.

I don't know the exact steps, but since no one has answered this, I took a guess!

fa3a · 01-21-2004, 09:02 AM

Yes i agree.. looks like I need to look at tune2fs code, since it detects somehow whether the fs has journal or not:
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Filesystem features: has_journal filetype needs_recovery sparse_super
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jtshaw · 01-21-2004, 09:07 AM

I don't run ext3 so I have no way of checking, but is the journal done in a file, or does it set aside part of the partition for it and not use a file like reiserfs does? If so you could just look for the journal file.

fa3a · 01-21-2004, 10:33 AM

yes, it looks like the way.. but I won't be really satisfied if it would be the only way.. because if so, then removing a journal, or how it often happens, if journal is corrupted, then it "means" that ext3 fs becomes ext2 again?? hm.. I'll look at tune2fs code..

jtshaw · 01-21-2004, 10:38 AM

That probably is the case. Ext3 is exactly the same as Ext2 with the exception of the journal. They did it that way so if you forgot Ext3 support in your kernel, or your journal was messed up, it could mount it as an ext2 and just not use the journal.

UltimaGuy · 01-22-2004, 02:13 AM

Yes, and I have seen that you can convert an existing ext2 partition into an ext3 by just adding an journal using the tune2fs command. I've forgotten the exact options, but I have seen it done!

fa3a · 01-22-2004, 03:37 AM

option is simple: tune2fs -j
anyway thanks!! it seems to be the correct way to detect if the UNMOUNTED filesystem is ext3 or ext2 by searching for its journal file.
For MOUNTED file system it's much simple -- via getmntent() and look for "ext3" in mnt_type member in mntent structure.