On Fri, Mar 24, 2023 at 09:57:51PM +0800, Ming Lei wrote:
Hello Jens,
Add IORING_OP_FUSED_CMD, it is one special URING_CMD, which has to
be SQE128. The 1st SQE(master) is one 64byte URING_CMD, and the 2nd
64byte SQE(slave) is another normal 64byte OP. For any OP which needs
to support slave OP, io_issue_defs[op].fused_slave needs to be set as 1,
and its ->issue() can retrieve/import buffer from master request's
fused_cmd_kbuf. The slave OP is actually submitted from kernel, part of
this idea is from Xiaoguang's ublk ebpf patchset, but this patchset
submits slave OP just like normal OP issued from userspace, that said,
SQE order is kept, and batching handling is done too.
Please see detailed design in commit log of the 2th patch, and one big
point is how to handle buffer ownership.
With this way, it is easy to support zero copy for ublk/fuse device.
Basically userspace can specify any sub-buffer of the ublk block request
buffer from the fused command just by setting 'offset/len'
in the slave SQE for running slave OP.
Wondering if this new OP can also be used to do larger IO (than
device limit) on nvme-passthrough?
For example, 1MB IO on NVMe than has 512k or 256K maximum transfer
size.
