Re: Ring Setup Question

[Jens Axboe <axboe@kernel.dk>]

On 4/23/20 8:38 AM, Daniel H wrote:
> I'm working on a implementation of for the Go language and I've been running
> into a failed test case that I can't understand. The test is setup in the
> following manner; first write some data into a file and then read the data
> back using the io_uring. The simple test case of reading back all the bytes
> passes. However, when using two reads to read half the amount of data what I
> observe is the second time the ring is entered (after the first read completes
> successfully) is that the resulting CQE doesn't match the UserData. The test
> uses a monotonically increasing value for UserData and the following debug
> messages show that each entry has a unique UserData field. I'm guessing
> the ring is setup properly, however I'm not sure how to proceed.
> 
> === RUN   TestRingFileReadWriterRead
> pre enter
> sq head: 0 tail: 1
> sq entries: [{Opcode:22 Flags:2 Ioprio:0 Fd:8 Offset:0
> Addr:824634362160 Len:7 UFlags:0 UserData:1 Anon0:[0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0 0 0 0 0]} {Opcode:0 Flags:0 Ioprio:0 Fd:0 Offset:0
> Addr:0 Len:0 UFlags:0 UserData:0 Anon0:[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0]}]
> cq head: 0 tail: 0
> cq entries: [{UserData:0 Res:0 Flags:0} {UserData:0 Res:0 Flags:0}]
> enter complete
> sq head: 1 tail: 1
> sq entries: [{Opcode:22 Flags:2 Ioprio:0 Fd:8 Offset:0
> Addr:824634362160 Len:7 UFlags:0 UserData:1 Anon0:[0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0 0 0 0 0]} {Opcode:0 Flags:0 Ioprio:0 Fd:0 Offset:0
> Addr:0 Len:0 UFlags:0 UserData:0 Anon0:[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0]}]
> cq head: 1 tail: 1
> cq entries: [{UserData:1 Res:7 Flags:0} {UserData:0 Res:0 Flags:0}]
> pre enter
> sq head: 1 tail: 2
> sq entries: [{Opcode:22 Flags:2 Ioprio:0 Fd:8 Offset:0
> Addr:824634362160 Len:7 UFlags:0 UserData:1 Anon0:[0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0 0 0 0 0]} {Opcode:22 Flags:2 Ioprio:0 Fd:8
> Offset:7 Addr:824634363240 Len:7 UFlags:0 UserData:2 Anon0:[0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]}]
> cq head: 1 tail: 1
> cq entries: [{UserData:1 Res:7 Flags:0} {UserData:0 Res:0 Flags:0}]
> enter complete
> sq head: 2 tail: 2
> sq entries: [{Opcode:22 Flags:2 Ioprio:0 Fd:8 Offset:0
> Addr:824634362160 Len:7 UFlags:0 UserData:1 Anon0:[0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0 0 0 0 0]} {Opcode:22 Flags:2 Ioprio:0 Fd:8
> Offset:7 Addr:824634363240 Len:7 UFlags:0 UserData
> :2 Anon0:[0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]}]
> cq head: 1 tail: 2
> cq entries: [{UserData:1 Res:7 Flags:0} {UserData:1 Res:7 Flags:0}]

I think it'll be hard to advise on what is going wrong here without
having a test case.

-- 
Jens Axboe