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SubjectRe: Collapse ext2 and 3 please
If ext2 and ext3 are different filesystems, why does my kernel panic if 
I include ext3 in the kernel make ext2 a module?


Helge Hafting wrote:
> John Richard Moser wrote:
>> Hash: SHA1
>> I know this has been mentioned before, or at least I *hope* it has.
> Take a look at history. Linus said that creating a journalled fs was
> fine, but they had to make it a new fs so as to not make ext2 unstable
> while working on it. Therefore - ext3. Now ext3 was based on ext2
> so it basically started out as a copy.
>> ext2 and ext3 are essentially the same, aren't they? I'm looking at a
>> diff, and other than ext2->ext3, I'm seeing things like:
>> - - mark_inode_dirty(inode);
>> + ext3_mark_inode_dirty(handle, inode);
>> and thinking
>> - - mark_inode_dirty(inode);
>> + if (fs->journaled)
>> + extjnl_mark_inode_dirty(handle, inode);
>> + else
>> +#endif
>> + mark_inode_dirty(inode);
>> would have been so much more appropriate.
> No, because:
> 1. Code withg lots of #ifdefs isn't popular here. So don't suggest it,
> because no argument will win this one.
> 2. Did it ever occur to you that some people want to support both
> ext2 and ext3 with the same kernel. Impossible with your scheme,
> and don't say "nobody needs that".
> 3. ext3 may evolve differently from ext2 with time. Common code
> makes people do things in suboptimal ways in order to keep
> commonality. There is _no_ commonality pressure when the
> sources are separate. ext3 developers are free to change their
> code in ways that could break operation of the non-journalling ext2.
> And vice-versa- ext2 is free do use ordering optimizations incompatible
> with journalling.
> 4. "Appropriate" doesn't matter. Readability and maintainability does.
> 5. Linus demanded two fs'es in this case, so there is no discussion.
>> I see entire functions that
>> are dropped and added; the dropped can stay, the added can be added,
>> they can be used conditionally. I also see mostly code that just was
>> copied verbatim, or was s/EXT2/EXT3/ or s/ext2/ext3/ . That's just not
>> appropriate.
> This is not much of a problem - a few kB wasted on keeping some
> identical copies of code. You might be able to establish a
> ext23_common.c, _if_ you can prove that the stuff therein really
> won't ever be different in ext2 and ext3.
>> The ext2 driver can even load up ext3 partitions without using the
>> journal, if it still behaves like it did in 2.4.20. I say collapse them
>> in on eachother.
> This was very useful during initial development, when ext3 couldn't
> really be trusted. It is still useful because it allows easy conversion
> of existing filesystems, and a single fsck. Compatibility might break
> someday though.
> The fs code may take very different approaches with time anyway,
> even if the disk layout remains compatible.
> Helge Hafting
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