On Mon, Jul 19, 2010 at 02:02:22PM -0400, Josef Bacik wrote: > On Mon, Jun 21, 2010 at 12:42:52PM +0200, Jan Kara wrote: > > block_prepare_write() can dirty freshly created buffer. This is a problem > > for data=journal mode because data buffers shouldn't be dirty unless they > > are undergoing checkpoint. So we have to tweak get_block function for > > data=journal mode to catch the case when block_prepare_write would dirty > > the buffer, do the work instead of block_prepare_write, and properly handle > > dirty buffer as data=journal mode requires it. > > > > It might be cleaner to avoid using block_prepare_write() for data=journal > > mode writes but that would require us to duplicate most of the function > > which isn't nice either... > > > > Signed-off-by: Jan Kara <jack@xxxxxxx> > > --- > > fs/ext3/inode.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++------- > > 1 files changed, 48 insertions(+), 8 deletions(-) > > > > diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c > > index ea33bdf..2b61cc4 100644 > > --- a/fs/ext3/inode.c > > +++ b/fs/ext3/inode.c > > @@ -993,6 +993,43 @@ out: > > return ret; > > } > > > > +static int ext3_journalled_get_block(struct inode *inode, sector_t iblock, > > + struct buffer_head *bh, int create) > > +{ > > + handle_t *handle = ext3_journal_current_handle(); > > + int ret; > > + > > + /* This function should ever be used only for real buffers */ > > + BUG_ON(!bh->b_page); > > + > > + ret = ext3_get_blocks_handle(handle, inode, iblock, 1, bh, create); > > + if (ret > 0) { > > + if (buffer_new(bh)) { > > + struct page *page = bh->b_page; > > + > > + /* > > + * This is a terrible hack to avoid block_prepare_write > > + * marking our buffer as dirty > > + */ > > + if (PageUptodate(page)) { > > + ret = ext3_journal_get_write_access(handle, bh); > > + if (ret < 0) > > + goto out; > > + unmap_underlying_metadata(bh->b_bdev, > > + bh->b_blocknr); > > + clear_buffer_new(bh); > > + set_buffer_uptodate(bh); > > + ret = ext3_journal_dirty_metadata(handle, bh); > > + if (ret < 0) > > + goto out; > > + } > > + } > > Hey Jan, > > It looks like in __block_prepare_write we zero out the end of the page if we're > not writing to the entire block, but you short-circuit this behavior with this > get_block. So it's possible that if we only write to half of the block, the > last half is going to have whatever stale data was in there before, right? > Thanks, > Oops, ignore me, nothing changes for the !PageUptodate() case, which is where the page zero'ing part happens. Carry on :), Josef -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html