On 5/12/22 10:38 PM, Hao Xu wrote:
> ? 2022/5/9 ??11:50, Jens Axboe ??:
>> If the application passes in IORING_FILE_INDEX_ALLOC as the file_slot,
>> then that's a hint to allocate a fixed file descriptor rather than have
>> one be passed in directly.
>>
>> This can be useful for having io_uring manage the direct descriptor space.
>>
>> Normal open direct requests will complete with 0 for success, and < 0
>> in case of error. If io_uring is asked to allocated the direct descriptor,
>> then the direct descriptor is returned in case of success.
>>
>> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>> ---
>> fs/io_uring.c | 32 +++++++++++++++++++++++++++++---
>> include/uapi/linux/io_uring.h | 9 +++++++++
>> 2 files changed, 38 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 8c40411a7e78..ef999d0e09de 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -4697,7 +4697,7 @@ static int io_openat2_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>> return __io_openat_prep(req, sqe);
>> }
>> -static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
>> +static int io_file_bitmap_get(struct io_ring_ctx *ctx)
>> {
>> struct io_file_table *table = &ctx->file_table;
>> unsigned long nr = ctx->nr_user_files;
>> @@ -4722,6 +4722,32 @@ static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
>> return -ENFILE;
>> }
>> +static int io_fixed_fd_install(struct io_kiocb *req, unsigned int issue_flags,
>> + struct file *file, unsigned int file_slot)
>> +{
>> + int alloc_slot = file_slot == IORING_FILE_INDEX_ALLOC;
>> + struct io_ring_ctx *ctx = req->ctx;
>> + int ret;
>> +
>> + if (alloc_slot) {
>> + io_ring_submit_lock(ctx, issue_flags);
>> + file_slot = io_file_bitmap_get(ctx);
>> + if (unlikely(file_slot < 0)) {
>> + io_ring_submit_unlock(ctx, issue_flags);
>> + return file_slot;
>> + }
>> + }
>> +
>> + ret = io_install_fixed_file(req, file, issue_flags, file_slot);
>> + if (alloc_slot) {
>> + io_ring_submit_unlock(ctx, issue_flags);
>> + if (!ret)
>> + return file_slot;
>
> Sorry, I missed onething, looks like this should be file_slot+1, as this
> is returned to the userspace. I refer to the previous open/accept direct
> feature, they see the file_index from userspace as number counted from
> one, so it'd better to keep it consistent.
We need to return the actual slot, not slot + 1. It's kind of an ugly
API, but what we had left to deal with. The actual slot number is what
most other things would fill into sqe->fd and set IOSQE_FIXED_FILE with,
not slot + 1.
--
Jens Axboe
