On Sun, Mar 29, 2020 at 5:05 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> 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. Thanks for comments, Christoph. If I understood you correctly, so the right way is to construct bio similar to bio_map_kern, but we have to use bio_add_page instead of bio_add_pc_page? As mentioned by Bart also Chaitanya, looks it's reasonable to add a helper for normal READ|WRITE operation to map and submit bio from the data buffer, but sure can be done later. Thanks!
