Commit 92cc9acf authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'fuse-update-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse 

Pull fuse updates from Miklos Szeredi:
 "Add support for io-uring communication between kernel and userspace
  using IORING_OP_URING_CMD (Bernd Schubert). Following features enable
  gains in performance compared to the regular interface:

   - Allow processing multiple requests with less syscall overhead

   - Combine commit of old and fetch of new fuse request

   - CPU/NUMA affinity of queues

  Patches were reviewed by several people, including Pavel Begunkov,
  io-uring co-maintainer"

* tag 'fuse-update-6.14' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse:
  fuse: prevent disabling io-uring on active connections
  fuse: enable fuse-over-io-uring
  fuse: block request allocation until io-uring init is complete
  fuse: {io-uring} Prevent mount point hang on fuse-server termination
  fuse: Allow to queue bg requests through io-uring
  fuse: Allow to queue fg requests through io-uring
  fuse: {io-uring} Make fuse_dev_queue_{interrupt,forget} non-static
  fuse: {io-uring} Handle teardown of ring entries
  fuse: Add io-uring sqe commit and fetch support
  fuse: {io-uring} Make hash-list req unique finding functions non-static
  fuse: Add fuse-io-uring handling into fuse_copy
  fuse: Make fuse_copy non static
  fuse: {io-uring} Handle SQEs - register commands
  fuse: make args->in_args[0] to be always the header
  fuse: Add fuse-io-uring design documentation
  fuse: Move request bits
  fuse: Move fuse_get_dev to header file
  fuse: rename to fuse_dev_end_requests and make non-static
parents 27560b37 2d4fde59

Documentation/filesystems/fuse-io-uring.rst

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.. SPDX-License-Identifier: GPL-2.0



=======================================

FUSE-over-io-uring design documentation

=======================================



This documentation covers basic details how the fuse

kernel/userspace communication through io-uring is configured

and works. For generic details about FUSE see fuse.rst.



This document also covers the current interface, which is

still in development and might change.



Limitations

===========

As of now not all requests types are supported through io-uring, userspace

is required to also handle requests through /dev/fuse after io-uring setup

is complete. Specifically notifications (initiated from the daemon side)

and interrupts.



Fuse io-uring configuration

===========================



Fuse kernel requests are queued through the classical /dev/fuse

read/write interface - until io-uring setup is complete.



In order to set up fuse-over-io-uring fuse-server (user-space)

needs to submit SQEs (opcode = IORING_OP_URING_CMD) to the /dev/fuse

connection file descriptor. Initial submit is with the sub command

FUSE_URING_REQ_REGISTER, which will just register entries to be

available in the kernel.



Once at least one entry per queue is submitted, kernel starts

to enqueue to ring queues.

Note, every CPU core has its own fuse-io-uring queue.

Userspace handles the CQE/fuse-request and submits the result as

subcommand FUSE_URING_REQ_COMMIT_AND_FETCH - kernel completes

the requests and also marks the entry available again. If there are

pending requests waiting the request will be immediately submitted

to the daemon again.



Initial SQE

-----------::



 |                                    |  FUSE filesystem daemon

 |                                    |

 |                                    |  >io_uring_submit()

 |                                    |   IORING_OP_URING_CMD /

 |                                    |   FUSE_URING_CMD_REGISTER

 |                                    |  [wait cqe]

 |                                    |   >io_uring_wait_cqe() or

 |                                    |   >io_uring_submit_and_wait()

 |                                    |

 |  >fuse_uring_cmd()                 |

 |   >fuse_uring_register()           |





Sending requests with CQEs

--------------------------::



 |                                           |  FUSE filesystem daemon

 |                                           |  [waiting for CQEs]

 |  "rm /mnt/fuse/file"                      |

 |                                           |

 |  >sys_unlink()                            |

 |    >fuse_unlink()                         |

 |      [allocate request]                   |

 |      >fuse_send_one()                     |

 |        ...                                |

 |       >fuse_uring_queue_fuse_req          |

 |        [queue request on fg queue]        |

 |         >fuse_uring_add_req_to_ring_ent() |

 |         ...                               |

 |          >fuse_uring_copy_to_ring()       |

 |          >io_uring_cmd_done()             |

 |       >request_wait_answer()              |

 |         [sleep on req->waitq]             |

 |                                           |  [receives and handles CQE]

 |                                           |  [submit result and fetch next]

 |                                           |  >io_uring_submit()

 |                                           |   IORING_OP_URING_CMD/

 |                                           |   FUSE_URING_CMD_COMMIT_AND_FETCH

 |  >fuse_uring_cmd()                        |

 |   >fuse_uring_commit_fetch()              |

 |    >fuse_uring_commit()                   |

 |     >fuse_uring_copy_from_ring()          |

 |      [ copy the result to the fuse req]   |

 |     >fuse_uring_req_end()                 |

 |      >fuse_request_end()                  |

 |       [wake up req->waitq]                |

 |    >fuse_uring_next_fuse_req              |

 |       [wait or handle next req]           |

 |                                           |

 |       [req->waitq woken up]               |

 |    <fuse_unlink()                         |

 |  <sys_unlink()                            |

Documentation/filesystems/index.rst

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@@ -98,6 +98,7 @@ Documentation for filesystem implementations. 
   hpfs

   fuse

   fuse-io

   fuse-io-uring

   inotify

   isofs

   nilfs2

fs/fuse/Kconfig

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@@ -63,3 +63,15 @@ config FUSE_PASSTHROUGH 
	  to be performed directly on a backing file.



	  If you want to allow passthrough operations, answer Y.



config FUSE_IO_URING

	bool "FUSE communication over io-uring"

	default y

	depends on FUSE_FS

	depends on IO_URING

	help

	  This allows sending FUSE requests over the io-uring interface and

          also adds request core affinity.



	  If you want to allow fuse server/client communication through io-uring,

	  answer Y

fs/fuse/Makefile

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@@ -15,5 +15,6 @@ fuse-y += iomode.o 
fuse-$(CONFIG_FUSE_DAX) += dax.o

fuse-$(CONFIG_FUSE_PASSTHROUGH) += passthrough.o

fuse-$(CONFIG_SYSCTL) += sysctl.o

fuse-$(CONFIG_FUSE_IO_URING) += dev_uring.o



virtiofs-y := virtio_fs.o

fs/fuse/dax.c

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@@ -240,11 +240,12 @@ static int fuse_send_removemapping(struct inode *inode, 


	args.opcode = FUSE_REMOVEMAPPING;

	args.nodeid = fi->nodeid;

	args.in_numargs = 2;

	args.in_args[0].size = sizeof(*inargp);

	args.in_args[0].value = inargp;

	args.in_args[1].size = inargp->count * sizeof(*remove_one);

	args.in_args[1].value = remove_one;

	args.in_numargs = 3;

	fuse_set_zero_arg0(&args);

	args.in_args[1].size = sizeof(*inargp);

	args.in_args[1].value = inargp;

	args.in_args[2].size = inargp->count * sizeof(*remove_one);

	args.in_args[2].value = remove_one;

	return fuse_simple_request(fm, &args);

}