Re: [PATCH v11 15/26] block: reexport bio_map_kern

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On 03/29/2020 08:05 AM, Christoph Hellwig wrote:
> On Sat, Mar 28, 2020 at 09:16:55AM -0700, Bart Van Assche wrote:
>> >There are more users in the Linux kernel of bio_add_pc_page() than only
>> >bio_map_kern(), e.g. the SCSI target pass-through code
>> >(drivers/target/target_core_pscsi.c). The code that uses bio_map_kern()
>> >is in patch 22/26: "block/rnbd: server: functionality for IO submission
>> >to file or block dev". Isn't that use case similar to the SCSI
>> >pass-through code? I think the RNBD server code also implements storage
>> >target functionality.
> No, it is not at all.  The RNBD case submits normal read/write bios, for
> which bio_map_kerl is the wrong interfac given that it
> uses bio_add_pc_page.  Read, write and other non-passthrough requests
> must use bio_add_page instead.
>

Since rw are most common operations, it'd be nice to have a helper
function for REQ_OP_[READ|WRITE] to map and submit bio from data buffer
with chaining to avoid code duplication in each driver which based on 
the bio_add_page().

I'd be happy to send a patch for that if that is acceptable.




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