On 7/13/20 4:55 PM, Daniele Salvatore Albano wrote: > Hi everyone, > > I am trying to use IORING_OP_FILES_UPDATE in combination with > IOSQE_IO_LINK and IORING_OP_RECV / IORING_OP_RECV as linked op but I > keep getting ECANCELED (errno 125). > > I am using io_uring (kernel 5.8.0-rc4 built 3 days ago) and liburing (tag 0.7). > > I went through the test cases and I wasn't able to find any > combination of the OP and the flag and I can't find any related docs > so I am not sure if the combo isn't allowed. > > Although I have found > https://github.com/torvalds/linux/blob/v5.8-rc5/fs/io_uring.c#L4926 > > if (sqe->flags || sqe->ioprio || sqe->rw_flags) > return -EINVAL; > > Not sure if this is the reason for which the linked operation is > failing, I don't see in the other *_prep sqe->flags being broadly > checked in general. > > I wrote two simple test cases that perform the following sequence of operations: > - open a local file (for the two test cases below /proc/cmdline) > - IORING_OP_FILES_UPDATE + IOSQE_IO_LINK (only in the first test case) > - IORING_OP_READ + IOSQE_FIXED_FILE > > Here a small test case to trigger the issue I am facing > > int main() { > struct io_uring ring = {0}; > uint32_t head, count = 0; > struct io_uring_sqe *sqe = NULL; > struct io_uring_cqe *cqe = NULL; > uint32_t files_map_count = 16; > const int *files_map_registered = malloc(sizeof(int) * files_map_count); > memset((void*)files_map_registered, 0, sizeof(int) * files_map_count); > > io_uring_queue_init(16, &ring, 0); > io_uring_register_files(&ring, files_map_registered, files_map_count); > > int fd = open("/proc/cmdline", O_RDONLY); > int fd_index = 10; > > sqe = io_uring_get_sqe(&ring); > io_uring_prep_files_update(sqe, &fd, 1, fd_index); > io_uring_sqe_set_flags(sqe, IOSQE_IO_LINK); > sqe->user_data = 1; > > char buffer[512] = {0}; > sqe = io_uring_get_sqe(&ring); > io_uring_prep_read(sqe, fd_index, &buffer, sizeof(buffer), 0); > io_uring_sqe_set_flags(sqe, IOSQE_FIXED_FILE); > sqe->user_data = 2; > > io_uring_submit_and_wait(&ring, 2); > > io_uring_for_each_cqe(&ring, head, cqe) { > count++; > > fprintf(stdout, "count = %d\n", count); > fprintf(stdout, "cqe->res = %d\n", cqe->res); > fprintf(stdout, "cqe->user_data = %llu\n", cqe->user_data); > fprintf(stdout, "cqe->flags = %u\n", cqe->flags); > } > > io_uring_cq_advance(&ring, count); > > io_uring_unregister_files(&ring); > io_uring_queue_exit(&ring); > > return 0; > } > > It will report for both the cqes res = -125 > > Instead if the code doesn't link and wait for the read it works as I > am expecting. > > int main() { > struct io_uring ring = {0}; > uint32_t head, count = 0; > char buffer[512] = {0}; > struct io_uring_sqe *sqe = NULL; > struct io_uring_cqe *cqe = NULL; > uint32_t files_map_count = 16; > const int *files_map_registered = malloc(sizeof(int) * files_map_count); > memset((void*)files_map_registered, 0, sizeof(int) * files_map_count); > > io_uring_queue_init(16, &ring, 0); > io_uring_register_files(&ring, files_map_registered, files_map_count); > > int fd = open("/proc/cmdline", O_RDONLY); > int fd_index = 10; > > sqe = io_uring_get_sqe(&ring); > io_uring_prep_files_update(sqe, &fd, 1, fd_index); > io_uring_sqe_set_flags(sqe, 0); > sqe->user_data = 1; > > int exit_loop = 0; > do { > io_uring_submit_and_wait(&ring, 1); > > io_uring_for_each_cqe(&ring, head, cqe) { > count++; > > fprintf(stdout, "count = %d\n", count); > fprintf(stdout, "cqe->res = %d\n", cqe->res); > fprintf(stdout, "cqe->user_data = %llu\n", cqe->user_data); > fprintf(stdout, "cqe->flags = %u\n", cqe->flags); > > if (cqe->user_data == 1) { > sqe = io_uring_get_sqe(&ring); > io_uring_prep_read(sqe, fd_index, &buffer, sizeof(buffer), 0); > io_uring_sqe_set_flags(sqe, IOSQE_FIXED_FILE); > sqe->user_data = 2; > } else { > if (cqe->res >= 0) { > fprintf(stdout, "buffer = <"); > fwrite(buffer, cqe->res, 1, stdout); > fprintf(stdout, ">\n"); > } > > exit_loop = 1; > } > } > > io_uring_cq_advance(&ring, count); > } while(exit_loop == 0); > > io_uring_unregister_files(&ring); > io_uring_queue_exit(&ring); > > return 0; > } > > The output here is > count = 1 > cqe->res = 1 > cqe->user_data = 1 > cqe->flags = 0 > count = 2 > cqe->res = 58 > cqe->user_data = 2 > cqe->flags = 0 > buffer = <initrd=....yada yada yada...> > > Is this the expected behaviour? If no, any hint? What am I doing wrong? > > If the expected behaviour is that IORING_OP_FILES_UPDATE can't be > linked, how can I use it properly to issue a read or another op that > requires to work with fds in a chain of operations? I think the sqe->flags should just be removed, as you're alluding to. Care to send a patch for that? Then I can queue it up. We can even mark it stable to ensure it gets back to older kernels. Probably just want to make it something ala: unsigned flags = READ_ONCE(sqe->flags); if (flags & (IOSQE_FIXED_FILE | IOSQE_BUFFER_SELECT)) return -EINVAL; as those flags don't make sense, but the rest do. -- Jens Axboe
