On 12/16/19 1:12 AM, Qu Wenruo wrote:
[BUG] There are several reports about vanilla `df` reports no available space, while `btrfs filesystem df` is still reporting tons of unallocated space. https://lore.kernel.org/linux-btrfs/CAJCQCtQEu_+nL_HByAWK2zKfg2Zhpm3Ezto+sA12wwV0iq8Ghg@xxxxxxxxxxxxxx/T/#t https://lore.kernel.org/linux-btrfs/CAJCQCtSWW4ageK56PdHtSmgrFrDf_Qy0PbxZ5LSYYCbr3Z10ug@xxxxxxxxxxxxxx/T/#t The example output from vanilla `df` would look like: Filesystem Size Used Avail Use% Mounted on /dev/loop0 7.4T 623G 0 100% /media/backup [CAUSE] There is a special check in btrfs_statfs(), which reset f_bavail: if (!mixed && total_free_meta - SZ_4M < block_rsv->size) buf->f_bavail = 0;
Why not just read fs_info->free_chunk_space and take that into account? The point is we want to tell the user there's no room left if we can't allocate a new chunk and we only have the global reserve space left. So just subtract the global reserve size from the total f_bavail as long as free_chunk_space is sufficient, otherwise fall back to the original calculation. Thanks,
Josef
