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ublk: lift checks out of ublk_{,un}map_io()

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ublk_map_io() and ublk_unmap_io() are no-ops for ublk devices that
enable user copy or zero copy, as well as for requests without data to
copy in the given direction. However, the implementation is a bit
convoluted, returning the full request data length and relying on the
caller to check the return value against the request length.
UBLK_F_SHMEM_ZC recently added branches to skip the ublk_{,un}map_io()
call for I/Os using a shared-memory buffer. This is a more logical place
for the device need_map and the ublk_need_{,un}map_req() checks, so move
them there from ublk_{,un}map_io().

Checking these conditions early also skips the expensive pointer-chasing
for the ublk_iod_is_shmem_zc() check in __ublk_complete_rq() for the
common case of a ublk device using user copy or zero copy.

Drop the req_op() filter in __ublk_complete_rq(), as it's redundant with
the ublk_need_unmap_req() check.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260803211441.2538144-9-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Caleb Sander Mateos
2026-08-03 15:14:40 -06:00
committed by Jens Axboe
parent d61d0f95e6
commit a8a79eba22
1 changed files with 19 additions and 51 deletions
Download Patch File Download Diff File Expand all files Collapse all files

70
drivers/block/ublk_drv.c
View File

@@ -1468,53 +1468,29 @@ static inline bool ublk_need_unmap_req(const struct request *req)
(req_op(req) == REQ_OP_READ || req_op(req) == REQ_OP_DRV_IN);
}
static unsigned int ublk_map_io(const struct ublk_queue *ubq,
const struct request *req,
static unsigned int ublk_map_io(const struct request *req,
const struct ublk_io *io)
{
const unsigned int rq_bytes = blk_rq_bytes(req);
struct iov_iter iter;
const int dir = ITER_DEST;
if (!ublk_need_map_io(ubq))
return rq_bytes;
if (import_ubuf(dir, u64_to_user_ptr(io->buf.addr), blk_rq_bytes(req),
&iter) < 0)
return 0;
/*
* no zero copy, we delay copy WRITE request data into ublksrv
* context and the big benefit is that pinning pages in current
* context is pretty fast, see ublk_pin_user_pages
*/
if (ublk_need_map_req(req)) {
struct iov_iter iter;
const int dir = ITER_DEST;
if (import_ubuf(dir, u64_to_user_ptr(io->buf.addr), rq_bytes,
&iter) < 0)
return 0;
return ublk_copy_user_pages(req, 0, &iter, dir);
}
return rq_bytes;
return ublk_copy_user_pages(req, 0, &iter, dir);
}
static unsigned int ublk_unmap_io(bool need_map,
const struct request *req,
static unsigned int ublk_unmap_io(const struct request *req,
const struct ublk_io *io)
{
const unsigned int rq_bytes = blk_rq_bytes(req);
struct iov_iter iter;
const int dir = ITER_SOURCE;
if (!need_map)
return rq_bytes;
if (import_ubuf(dir, u64_to_user_ptr(io->buf.addr), io->res, &iter) < 0)
return 0;
if (ublk_need_unmap_req(req)) {
struct iov_iter iter;
const int dir = ITER_SOURCE;
if (import_ubuf(dir, u64_to_user_ptr(io->buf.addr), io->res,
&iter) < 0)
return 0;
return ublk_copy_user_pages(req, 0, &iter, dir);
}
return rq_bytes;
return ublk_copy_user_pages(req, 0, &iter, dir);
}
static bool ublk_validate_req(const struct ublk_queue *ubq,
@@ -1590,22 +1566,13 @@ static inline void __ublk_complete_rq(struct request *req, struct ublk_io *io,
goto exit;
}
/*
* FLUSH, DISCARD or WRITE_ZEROES usually won't return bytes returned, so end them
* directly.
*
* Both the two needn't unmap.
*/
if (req_op(req) != REQ_OP_READ && req_op(req) != REQ_OP_WRITE &&
req_op(req) != REQ_OP_DRV_IN)
goto exit;
/* shmem zero copy: no data to unmap, pages already shared */
if (ublk_iod_is_shmem_zc(req->mq_hctx->driver_data, req->tag))
if (!need_map || !ublk_need_unmap_req(req) ||
ublk_iod_is_shmem_zc(req->mq_hctx->driver_data, req->tag))
goto exit;
/* for READ request, writing data in iod->addr to rq buffers */
unmapped_bytes = ublk_unmap_io(need_map, req, io);
unmapped_bytes = ublk_unmap_io(req, io);
/*
* Extremely impossible since we got data filled in just before
@@ -1771,10 +1738,11 @@ static bool ublk_start_io(const struct ublk_queue *ubq, struct request *req,
unsigned mapped_bytes;
/* shmem zero copy: skip data copy, pages already shared */
if (ublk_iod_is_shmem_zc(ubq, req->tag))
if (!ublk_need_map_io(ubq) || !ublk_need_map_req(req) ||
ublk_iod_is_shmem_zc(ubq, req->tag))
return true;
mapped_bytes = ublk_map_io(ubq, req, io);
mapped_bytes = ublk_map_io(req, io);
/* partially mapped, update io descriptor */
if (unlikely(mapped_bytes != blk_rq_bytes(req))) {