Re: [PATCH RFC v7 06/16] fuse: {uring} Handle SQEs - register commands

Bernd Schubert
2024-12-03T13:49:23Z

On 12/3/24 14:24, Pavel Begunkov wrote:
> On 11/27/24 13:40, Bernd Schubert wrote:
>> This adds basic support for ring SQEs (with opcode=IORING_OP_URING_CMD).
>> For now only FUSE_URING_REQ_FETCH is handled to register queue entries.
>>
>> Signed-off-by: Bernd Schubert <bschubert@ddn.com>
>> ---
>>   fs/fuse/Kconfig           |  12 ++
>>   fs/fuse/Makefile          |   1 +
>>   fs/fuse/dev.c             |   4 +
>>   fs/fuse/dev_uring.c       | 318 ++++++++++++++++++++++++++++++++++++
>> ++++++++++
>>   fs/fuse/dev_uring_i.h     | 115 +++++++++++++++++
>>   fs/fuse/fuse_i.h          |   5 +
>>   fs/fuse/inode.c           |  10 ++
>>   include/uapi/linux/fuse.h |  67 ++++++++++
>>   8 files changed, 532 insertions(+)
>>
>
>  diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
>> new file mode 100644
>> index
>> 0000000000000000000000000000000000000000..af9c5f116ba1dcf6c01d0359d1a06491c92c32f9
>> --- /dev/null
>> +++ b/fs/fuse/dev_uring.c
> ...
>> +
>> +/*
>> + * fuse_uring_req_fetch command handling
>> + */
>> +static void _fuse_uring_fetch(struct fuse_ring_ent *ring_ent,
>> +                  struct io_uring_cmd *cmd,
>> +                  unsigned int issue_flags)
>> +{
>> +    struct fuse_ring_queue *queue = ring_ent->queue;
>> +
>> +    spin_lock(&queue->lock);
>> +    fuse_uring_ent_avail(ring_ent, queue);
>> +    ring_ent->cmd = cmd;
>> +    spin_unlock(&queue->lock);
>> +}
>> +
>> +/*
>> + * sqe->addr is a ptr to an iovec array, iov[0] has the headers, iov[1]
>> + * the payload
>> + */
>> +static int fuse_uring_get_iovec_from_sqe(const struct io_uring_sqe *sqe,
>> +                     struct iovec iov[FUSE_URING_IOV_SEGS])
>> +{
>> +    struct iovec __user *uiov = u64_to_user_ptr(READ_ONCE(sqe->addr));
>> +    struct iov_iter iter;
>> +    ssize_t ret;
>> +
>> +    if (sqe->len != FUSE_URING_IOV_SEGS)
>> +        return -EINVAL;
>> +
>> +    /*
>> +     * Direction for buffer access will actually be READ and WRITE,
>> +     * using write for the import should include READ access as well.
>> +     */
>> +    ret = import_iovec(WRITE, uiov, FUSE_URING_IOV_SEGS,
>> +               FUSE_URING_IOV_SEGS, &iov, &iter);
>
> You're throwing away the iterator, I'd be a bit cautious about it.
> FUSE_URING_IOV_SEGS is 2, so it should avoid ITER_UBUF, but Jens
> can say if it's abuse of the API or not.
>
> Fwiw, it's not the first place I know of that just want to get
> an iovec avoiding playing games with different iterator modes.

Shall I create new exported function like import_iovec_from_user()
that duplicates all the parts from __import_iovec()? I could also
let __import_iovec() use that new function, although there will be
less inlining with -02.

>
>
>> +    if (ret < 0)
>> +        return ret;
>> +
>> +    return 0;
>> +}
>> +
>> +static int fuse_uring_fetch(struct io_uring_cmd *cmd, unsigned int
>> issue_flags,
>> +                struct fuse_conn *fc)
>> +{
>> +    const struct fuse_uring_cmd_req *cmd_req = io_uring_sqe_cmd(cmd-
>> >sqe);
>
> You need to check that the ring is setup with SQE128.
>
> (!(issue_flags & IO_URING_F_SQE128))
>     // fail
>
>> +    struct fuse_ring *ring = fc->ring;
>> +    struct fuse_ring_queue *queue;
>> +    struct fuse_ring_ent *ring_ent;
>> +    int err;
>> +    struct iovec iov[FUSE_URING_IOV_SEGS];
>> +
>> +    err = fuse_uring_get_iovec_from_sqe(cmd->sqe, iov);
>> +    if (err) {
>> +        pr_info_ratelimited("Failed to get iovec from sqe, err=%d\n",
>> +                    err);
>> +        return err;
>> +    }
>> +
>> +    err = -ENOMEM;
>> +    if (!ring) {
>> +        ring = fuse_uring_create(fc);
>> +        if (!ring)
>> +            return err;
>> +    }
>> +
>> +    queue = ring->queues[cmd_req->qid];
>> +    if (!queue) {
>> +        queue = fuse_uring_create_queue(ring, cmd_req->qid);
>> +        if (!queue)
>> +            return err;
>> +    }
>> +
>> +    /*
>> +     * The created queue above does not need to be destructed in
>> +     * case of entry errors below, will be done at ring destruction
>> time.
>> +     */
>> +
>> +    ring_ent = kzalloc(sizeof(*ring_ent), GFP_KERNEL_ACCOUNT);
>> +    if (ring_ent == NULL)
>> +        return err;
>> +
>> +    INIT_LIST_HEAD(&ring_ent->list);
>> +
>> +    ring_ent->queue = queue;
>> +    ring_ent->cmd = cmd;
>
> nit: seems it's also set immediately after in
> _fuse_uring_fetch().
>
>> +
>> +    err = -EINVAL;
>> +    if (iov[0].iov_len < sizeof(struct fuse_uring_req_header)) {
>> +        pr_info_ratelimited("Invalid header len %zu\n", iov[0].iov_len);
>> +        goto err;
>> +    }
>> +
> ...
>> +/*
>> + * Entry function from io_uring to handle the given passthrough command
>> + * (op cocde IORING_OP_URING_CMD)
>> + */
>> +int fuse_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
>> +{
>> +    struct fuse_dev *fud;
>> +    struct fuse_conn *fc;
>> +    u32 cmd_op = cmd->cmd_op;
>> +    int err;
>> +
>> +    /* Disabled for now, especially as teardown is not implemented
>> yet */
>> +    pr_info_ratelimited("fuse-io-uring is not enabled yet\n");
>> +    return -EOPNOTSUPP;
>
> Do compilers give warnings about such things? Unreachable code, maybe.
> I don't care much, but if they do to avoid breaking CONFIG_WERROR you
> might want to do sth about it. E.g. I'd usually mark the function
> __maybe_unused and not set it into fops until a later patch.

I don't get any warning, but I can also do what you suggest.

Thanks,
Bernd