(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@gmail.com> 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-mountin...
http://en.wikipedia.org/wiki/Extended_file_attributes
On Sun, Feb 3, 2013 at 12:26 AM, Rami Rosen <roszenrami@gmail.com> 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@gmail.com> 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@gmail.com> 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@gmail.com> 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@gmail.com> 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
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