On Mon, Mar 13, 2017 at 03:52:13PM +0800, Qu Wenruo wrote:
> btrfs_qgroup_release/free_data() only returns 0 or minus error
> number(ENOMEM is the only possible error).

btrfs_qgroup_release_data -> __btrfs_qgroup_release_data
will not allocate the ulist anymore, and there are no errors propagated
from clear_record_extent_bits (just 0), but there are still some
unhandled cases. So here a negative value should be expected anyway.

> This is normally good enough, but sometimes we need the accurate byte
> number it freed/released.
> 
> Change it to return actually released/freed bytenr number instead of 0
> for success.
> And slightly modify related extent_changeset structure, since in btrfs
> one none-hole data extent won't be larger than 128M, so "unsigned int"
> is large enough for the use case.

> -     u64 bytes_changed;
> +     unsigned int bytes_changed;

> @@ -2875,6 +2875,7 @@ static int __btrfs_qgroup_release_data(struct inode 
> *inode, u64 start, u64 len,
>               btrfs_qgroup_free_refroot(BTRFS_I(inode)->root->fs_info,
>                               BTRFS_I(inode)->root->objectid,
>                               changeset.bytes_changed);
> +     ret = changeset.bytes_changed;

This relies on the 128M limit, which will fit to int when assigned. I'm
thinking about the signedness, it makes sense to use unsigned for
bytes_changed, but we also need the negative error returned. Probably
ok.

>  out:
>       ulist_release(&changeset.range_changed);
>       return ret;
--
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