ext2 inode size patch - RE: PR kern/124621

Kostik Belousov kostikbel at gmail.com
Thu Dec 4 02:51:34 PST 2008

On Thu, Dec 04, 2008 at 07:15:05AM +0000, Bruce M. Simpson wrote:
> Hi,
> The inode size for the ext3 filesystem which Gentoo created for my last 
> install defaulted to 256 bytes, so I got bit by this problem.
> I can't speak for the write path. but the read path looks just fine to 
> me, and the patch should go in ASAP.
> Josh Carroll wrote:
> >>Ok, I describe my concern once more. I do not object against the checking
> >>of the inode size. But, if inode size is changed, then some data is added
> >>to the inode, that could (and usually does, otherwise why extend it ?)
> >>change intrerpetation of the inode. Thus, we need a verification of the
> >>fact that simply ignoring added fields does not damage filesystem or
> >>cause user data corruption. Verification != testing.
> >>    
> If folk are paranoid, then add a check for dynamic inode size and 
> disable ext2fs writes by downgrading the mount in that case (We can do 
> that, right? Can someone make sure Josh gets the help he needs here?)
> As Josh points out, the ext2 inode size is stored in the superblock. 
> Whilst it may vary between ext2 filesystems, *the inode size itself does 
> not appear to be something which one can modify in an existing ext2/3 
> filesystem*.
> Older ext2 filesystems may not contain the inode size field in the 
> superblock, and the patch appears to default to 128 for that case. The 
> double indirection thus introduced doesn't concern me, our ext2fs is not 
> performance critical code, and the superblock is likely to sit in L2/L3 
> cache anyway (note: content free argument).
> Thanks to Josh for fixing this problem.

Bruce, feel free to commit the patch.

I do not want to spend time on ext2 in any form, and due to our (only
partly jokingly) rule of the "last committer is the owner", I do not
want to analyze ext2 bug reports after.
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