Re: [PATCH v1 02/11] dm-pcache: add backing device management

[Dongsheng Yang <dongsheng.yang@linux.dev>]

在 7/1/2025 9:56 PM, Jonathan Cameron 写道:
> On Tue, 24 Jun 2025 07:33:49 +0000
> Dongsheng Yang <dongsheng.yang@linux.dev> wrote:
>
>> This patch introduces *backing_dev.{c,h}*, a self-contained layer that
>> handles all interaction with the *backing block device* where cache
>> write-back and cache-miss reads are serviced.  Isolating this logic
>> keeps the core dm-pcache code free of low-level bio plumbing.
>>
>> * Device setup / teardown
>>    - Opens the target with `dm_get_device()`, stores `bdev`, file and
>>      size, and initialises a dedicated `bioset`.
>>    - Gracefully releases resources via `backing_dev_stop()`.
>>
>> * Request object (`struct pcache_backing_dev_req`)
>>    - Two request flavours:
>>      - REQ-type – cloned from an upper `struct bio` issued to
>>        dm-pcache; trimmed and re-targeted to the backing LBA.
>>      - KMEM-type – maps an arbitrary kernel memory buffer
>>        into a freshly built.
>>    - Private completion callback (`end_req`) propagates status to the
>>      upper layer and handles resource recycling.
>>
>> * Submission & completion path
>>    - Lock-protected submit queue + worker (`req_submit_work`) let pcache
>>      push many requests asynchronously, at the same time, allow caller
>>      to submit backing_dev_req in atomic context.
>>    - End-io handler moves finished requests to a completion list processed
>>      by `req_complete_work`, ensuring callbacks run in process context.
>>    - Direct-submit option for non-atomic context.
>>
>> * Flush
>>    - `backing_dev_flush()` issues a flush to persist backing-device data.
>>
>> Signed-off-by: Dongsheng Yang <dongsheng.yang@linux.dev>
>> ---
>>   drivers/md/dm-pcache/backing_dev.c | 292 +++++++++++++++++++++++++++++
>>   drivers/md/dm-pcache/backing_dev.h |  88 +++++++++
>>   2 files changed, 380 insertions(+)
>>   create mode 100644 drivers/md/dm-pcache/backing_dev.c
>>   create mode 100644 drivers/md/dm-pcache/backing_dev.h
>> +
>> +struct pcache_backing_dev_req *backing_dev_req_create(struct pcache_backing_dev *backing_dev,
>> +						struct pcache_backing_dev_req_opts *opts)
>> +{
>> +	if (opts->type == BACKING_DEV_REQ_TYPE_REQ)
>> +		return req_type_req_create(backing_dev, opts);
>> +	else if (opts->type == BACKING_DEV_REQ_TYPE_KMEM)
>>
> returned in earlier branch so go with simpler
>
> 	if (opts->type..)

Hi Jonathan,

This looks good, I am willing to do this change.


Thanx

Dongsheng

> Or use a switch statement if you expect to get more entries in this over time.
>
>> +		return kmem_type_req_create(backing_dev, opts);
>> +
>> +	return NULL;
>> +}
>> +
>> +void backing_dev_flush(struct pcache_backing_dev *backing_dev)
>> +{
>> +	blkdev_issue_flush(backing_dev->dm_dev->bdev);
>> +}
>