On Fri, 2008-03-21 at 11:48 +0530, Aneesh Kumar K.V wrote:
> ext4_ext_get_blocks returns number of blocks allocated with buffer head
> unmapped for a read from prealloc space. This is needed so that delayed
> allocation doesn't do block reservation for prealloc space since the blocks
> are already resevred on disk. Fix ext4_ext_get_blocks to not return greater
> than max_blocks and also mark the buffer head unwritten. Some code path tries
> to read the block if buffer_head is not new and no uptodate. Marking the buffer
> head unwritten avoid this reading.
>
Seems this patch fixes two bugs together, it would be nice to split to
two as they cause two different problems.
To fix the bh->b_size warning solof founds for delayed allocation, I
would say we need to fix it in ext4_get_blocks_handle() (for indirect
files) and ext4_ext_get_blocks()(for extent files) both, not allowing
returning b_size greater than what the caller asking for. Also, the
patch below seems only address the preallocation map case, we need to
fix in in general block lookup case.
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> ---
> fs/ext4/extents.c | 14 +++++++++++++-
> 1 files changed, 13 insertions(+), 1 deletions(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index d6ae40a..edd1bf2 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2600,8 +2600,20 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
> }
> if (create == EXT4_CREATE_UNINITIALIZED_EXT)
> goto out;
> - if (!create)
> + if (!create) {
> + /*
> + * We have blocks reserved already. We
> + * return allocated blocks so that delalloc
> + * won't do block reservation for us. But
> + * the buffer head will be unmapped so that
> + * a read from the block return 0
> + */
> + if (allocated > max_blocks)
> + allocated = max_blocks;
> + /* mark the buffer unwritten */
> + __set_bit(BH_Unwritten, &bh_result->b_state);
> goto out2;
> + }
>
> ret = ext4_ext_convert_to_initialized(handle, inode,
> path, iblock,
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