Re: [PATCH v2] zloop: zero out only the unread tail of short reads

[Damien Le Moal <dlemoal@kernel.org>]

On 2026/07/30 16:26, Shin'ichiro Kawasaki wrote:
> zloop_complete_rq() handles a short read from a zone's backing file by
> zero-filling every bio in the request. This is correct when the entire
> request is beyond the written part of the zone. When a read request
> straddles the boundary between written and unwritten data, read_iter()
> returns a partial byte count and zloop then zeroes the whole request
> even for the partially read area with valid data.
> 
> Such an unexpected zero data read was observed with fio test script
> t/zbd/test-zbd-support and its test case 69, failing with "bad magic
> header 0".
> 
> Avoid the unexpected zero data read by zeroing out only the unread tail
> part. When read data size cmd->ret is smaller than the request size,
> call the new helper function zloop_fill_zero_rq() that walks through
> each bio_vec and fills zeros from the specified start offset.
> 
> Fixes: eb0570c7df23 ("block: new zoned loop block device driver")
> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>


-- 
Damien Le Moal
Western Digital Research