Aneesh Kumar K.V wrote:
> We need to mark the buffer_head mapping prealloc space
> as new during write_begin. Otherwise we don't zero out the
> page cache content properly for a partial write. This will
> cause file corruption with preallocation.
>
> Also use block number -1 as the fake block number so that
> unmap_underlying_metadata doesn't drop wrong buffer_head
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
>
> ---
> fs/ext4/inode.c | 10 ++++++++++
> 1 files changed, 10 insertions(+), 0 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index e91f978..12dcfab 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2323,6 +2323,16 @@ static int ext4_da_get_block_prep(struct inode *inode, sector_t iblock,
> set_buffer_delay(bh_result);
> } else if (ret > 0) {
> bh_result->b_size = (ret << inode->i_blkbits);
> + /*
> + * With sub-block writes into unwritten extents
> + * we also need to mark the buffer as new so that
> + * the unwritten parts of the buffer gets correctly zeroed.
> + */
> + if (buffer_unwritten(bh_result)) {
> + bh_result->b_bdev = inode->i_sb->s_bdev;
> + set_buffer_new(bh_result);
> + bh_result->b_blocknr = -1;
> + }
> ret = 0;
> }
>
Ok, I guess this seems like the safest approach. Long term we should
look really hard at the state & block nr of these buffer heads, but I
agree that keeping the changes restricted to the preallocation path for
now is safest.
-Eric
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