Messages in this thread | | | Date | Wed, 12 Mar 2008 11:53:51 +0100 | From | Jan Kara <> | Subject | Re: [RFC, PATCH 6/6] ext3: do not write to the disk when mounting a dirty read-only filesystem |
| |
On Wed 12-03-08 02:42:46, Duane Griffin wrote: > On Tue, Mar 11, 2008 at 04:11:23PM +0100, Jan Kara wrote: > > Actually, this is nastier than it looks - currently fs, asks > > ext3_sb_getblk() for block 'a' and it gets buffer head with b_blocknr == 'b' > > instead. > > Note that it will be a different device as well, in the case of an > external journal. > > > So when remounting you'd have to rewrite these buffers with > > original block numbers which is not really possible. So I think > > remapping will have to be solved differently, like providing buffer > > head with correct b_blocknr but taking care when reading data to it and > > reading them from elsewhere. Actually, this has to be done anyway > > because JBD escapes data in the journal and you have to do unescaping > > when reading data... > > Hmm, I'll think about this and try to get something working. As a quick > proof-of-concept hack, getting both buffers then overwriting the fs > block's data with the unescaped journal data should do the trick, right? Yes, it should, but you should take care for users that do things like:
getblk(a) ll_rw_block(READ, a)
or even
getblk(a) submit_bh(a)
I'm not sure if there are any in ext3/ext4 but it definitely needs checking.
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
| |