On 3/21/25 18:48, Caleb Sander Mateos wrote:
For uring_cmd operations with fixed buffers, the fixed buffer lookup
happens in io_uring_cmd_import_fixed(), called from the ->uring_cmd()
implementation. A ->uring_cmd() implementation could return -EAGAIN on
the initial issue for any reason before io_uring_cmd_import_fixed().
For example, nvme_uring_cmd_io() calls nvme_alloc_user_request() first,
which can return -EAGAIN if all tags in the tag set are in use.
That's up to command when it resolves the buffer, you can just
move the call to io_import_reg_buf() earlier in nvme cmd code
and not working it around at the io_uring side.
In general, it's a step back, it just got cleaned up from the
mess where node resolution and buffer imports were separate
steps and duplicate by every single request type that used it.
This ordering difference is observable when using
UBLK_U_IO_{,UN}REGISTER_IO_BUF SQEs to modify the fixed buffer table.
If the uring_cmd is followed by a UBLK_U_IO_UNREGISTER_IO_BUF operation
that unregisters the fixed buffer, the uring_cmd going async will cause
the fixed buffer lookup to fail because it happens after the unregister.
Move the fixed buffer lookup out of io_uring_cmd_import_fixed() and
instead perform it in io_uring_cmd() before calling ->uring_cmd().
io_uring_cmd_import_fixed() now only initializes an iov_iter from the
existing fixed buffer node. This division of responsibilities makes
sense as the fixed buffer lookup is an io_uring implementation detail
and independent of the ->uring_cmd() implementation. It also cuts down
on the need to pass around the io_uring issue_flags.
Signed-off-by: Caleb Sander Mateos <csander@xxxxxxxxxxxxxxx>
Fixes: 27cb27b6d5ea ("io_uring: add support for kernel registered bvecs")
---
drivers/nvme/host/ioctl.c | 10 ++++------
include/linux/io_uring/cmd.h | 6 ++----
io_uring/rsrc.c | 6 ++++++
io_uring/rsrc.h | 2 ++
io_uring/uring_cmd.c | 10 +++++++---
5 files changed, 21 insertions(+), 13 deletions(-)
diff --git a/drivers/nvme/host/ioctl.c b/drivers/nvme/host/ioctl.c
index fe9fb80c6a14..3fad74563b9e 100644
--- a/drivers/nvme/host/ioctl.c
+++ b/drivers/nvme/host/ioctl.c
@@ -112,12 +112,11 @@ static struct request *nvme_alloc_user_request(struct request_queue *q,
--
Pavel Begunkov
