io_uring_prep_files_update(3) liburing Manual io_uring_prep_files_update(3)

io_uring_prep_files_update - prepare a registered file update request

#include <liburing.h>
void io_uring_prep_files_update(struct io_uring_sqe *sqe,
                                int *fds,
                                unsigned nr_fds,
                                int offset);

The io_uring_prep_files_update(3) function prepares a request for updating a number of previously registered file descriptors. The submission queue entry sqe is setup to use the file descriptor array pointed to by fds and of nr_fds in length to update that amount of previously registered files starting at offset offset.

Once a previously registered file is updated with a new one, the existing entry is updated and then removed from the table. This operation is equivalent to first unregistering that entry and then inserting a new one, just bundled into one combined operation.

If offset is specified as IORING_FILE_INDEX_ALLOC, io_uring will allocate free direct descriptors instead of having the application to pass, and store allocated direct descriptors into fds array, cqe->res will return the number of direct descriptors allocated.


These are the errors that are reported in the CQE res field. On success, res will contain the number of successfully updated file descriptors. On error, the following errors can occur.

The kernel was unable to allocate memory for the request.
One of the fields set in the SQE was invalid.
The kernel was unable to copy in the memory pointed to by fds.
On of the descriptors located in fds didn't refer to a valid file descriptor, or one of the file descriptors in the array referred to an io_uring instance.
The product of offset and nr_fds exceed the valid amount or overflowed.

As with any request that passes in data in a struct, that data must remain valid until the request has been successfully submitted. It need not remain valid until completion. Once a request has been submitted, the in-kernel state is stable. Very early kernels (5.4 and earlier) required state to be stable until the completion occurred. Applications can test for this behavior by inspecting the IORING_FEAT_SUBMIT_STABLE flag passed back from io_uring_queue_init_params(3).

io_uring_get_sqe(3), io_uring_submit(3), io_uring_register(2)

March 13, 2022 liburing-2.2