Linux Kernel Networking document (free, 178 pages doc)

[Greg Freemyer]

(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 at 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-mounting-dirty-ext4-filesystems
>
>http://en.wikipedia.org/wiki/Extended_file_attributes
>
>On Sun, Feb 3, 2013 at 12:26 AM, Rami Rosen <roszenrami at 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 at 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 at 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 at 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 at 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
>> >> >>>>
>> >> >>>> _______________________________________________
>> >> >>>> Kernelnewbies mailing list
>> >> >>>> Kernelnewbies at kernelnewbies.org
>> >> >>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>> >> >>>
>> >> >>>
>> >> >
>> >
>> >
>>
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