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? Sorry for the silly questions! Thanks! Daniele
