(Why is this a top-posted message thread? Please stop creating these.) Only the first link says that the ext2 driver can mount a ext4 filesystem (if the journal is clean). I'm confident that is wrong. Ext4 has several on-disk features that are not backward compatible. There is a binary set of flags which is set at mkfs time as to which of those features were enabled by mkfs.ext4. A ext3 doc would only describe a ext4 filesystem with all of those flags off. Thus a ext3 doc describing the on disk structure is not a waste of time, but it becomes a subset of a full ext4 doc describing the on disk structure. I would recommend that documenting that set of flags be the first documentation effort. Greg Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: >generally, anything u write for ext2, should still be valid for ext3, >and >ext4. in the sense that the features are backward compatible. sizing >limits may have increased, but OLD working mechanism should still be >valid....except for some. > >so ext2 fs should still be mountable as ext4, but not vice versa, once >some >flag is enabled (I think it is xattr). and if the flag is not enabled, >and >the journal logs is clean, then ext4 fs is also mountable as ext2 fs: > >http://superuser.com/questions/408822/ext4-converted-mounted-as-ext2 > >http://computer-forensics.sans.org/blog/2011/06/14/digital-forensics-mounting-dirty-ext4-filesystems > >http://en.wikipedia.org/wiki/Extended_file_attributes > >On Sun, Feb 3, 2013 at 12:26 AM, Rami Rosen <roszenrami@xxxxxxxxx> >wrote: > >> Hi, >> > ext2 and ext3 are kind of obsolete now. >> >> Indeed, ext4 was integrated into Linux kernel back in 2008. >> Amongs its known features which do not exist in ext3 are support for >> huge files (like 1 EB (exabyte or somtimes termed exbibyte); 1 EB >is >> 1024 PB (petabyte) whereas >> 1 PB is 1024 TB (terabyte). >> a directory can contain a maximum of 64,000 subdirectories (whereas >we >> have 32,000 in ext3) >> Amongst its other features are Journal checksumming, Multiblock >> allocator, Faster file system checking and more. >> >> >> If you prefer to start with simpler implementations, ext3 is of >course >> simpler, and of course ext2 is even simpler than ext3. >> >> But in case you intend to start with ext2/ext3, and later perform >> a pass on all your documentation to update it to ext4, take into >> consideration that this will take quite a time; depending on how deep >> you intend to delve into implementation details. >> >> Good luck! >> >> Regards, >> Rami Rosen >> http://ramirose.wix.com/ramirosen >> >> >> >> On Sat, Feb 2, 2013 at 11:43 AM, Shubham Sharma >> <kernel.shubham@xxxxxxxxx> wrote: >> > Hi, >> > >> > I understand that ext2 and ext3 are kind of obsolete now. But >AFAIK, >> there >> > is not much difference in ext3 and ext4. >> > >> > Moreover for a newbie , it is better to start with ext3. What you >think ? >> > >> > Regards >> > Shubham >> > >> > >> > On Fri, Feb 1, 2013 at 2:15 AM, Rami Rosen <roszenrami@xxxxxxxxx> >wrote: >> >> >> >> Hi, >> >> Have you considered to start with ext4? >> >> it seems that ext3, ext2 are a bit out of fashion, >> >> >> >> Regards, >> >> Rami Rosen >> >> http://ramirose.wix.com/ramirosen >> >> >> >> >> >> On Thu, Jan 31, 2013 at 8:58 PM, shubham ><kernel.shubham@xxxxxxxxx> >> wrote: >> >> > Thanks Rami, >> >> > >> >> > I am also trying to understand ext3 and write some document for >the >> >> > same. >> >> > >> >> > Regards >> >> > Shubham >> >> > >> >> > >> >> > On 31-Jan-13 12:51 AM, Rami Rosen wrote: >> >> >> >> >> >> HI, >> >> >> I will try to write something for Linux Filesystems (and maybe >for >> >> >> other subsystems) but this will probably take a lot of time. >> >> >> >> >> >> Regards, >> >> >> Rami Rosen >> >> >> http://ramirose.wix.com/ramirosen >> >> >> >> >> >> >> >> >> On Wed, Jan 30, 2013 at 5:44 PM, shubham ><kernel.shubham@xxxxxxxxx> >> >> >> wrote: >> >> >>> >> >> >>> Thanks for sharing the document. >> >> >>> >> >> >>> I hope we could have such documents for other subsystems as >well. >> >> >>> >> >> >>> Regards >> >> >>> Shubham >> >> >>> >> >> >>> >> >> >>> On 28-Jan-13 10:23 PM, Rami Rosen wrote: >> >> >>>> >> >> >>>> Hi everyone, >> >> >>>> You can find here an up to date and detailed document in pdf >(178 >> >> >>>> pages) about Linux Kernel Networking; going deep into design >and >> >> >>>> implementation details as well as the theory behind it: >> >> >>>> >> http://media.wix.com/ugd//295986_931b8bcf34d93419d46e05b5aa5d0216.pdf >> >> >>>> >> >> >>>> I believe that developers/sysadmins/researchers/students may >find >> >> >>>> help >> >> >>>> with it. >> >> >>>> >> >> >>>> >> >> >>>> regards, >> >> >>>> Rami Rosen >> >> >>>> >> >> >>>> http://ramirose.wix.com/ramirosen >> >> >>>> >> >> >>>> _______________________________________________ >> >> >>>> Kernelnewbies mailing list >> >> >>>> Kernelnewbies@xxxxxxxxxxxxxxxxx >> >> >>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> >> >>> >> >> >>> >> >> > >> > >> > >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies@xxxxxxxxxxxxxxxxx >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >> -- Sent from my Android phone with K-9 Mail. 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