| .\" Copyright (C) 2023 Jens Axboe <axboe@kernel.dk> |
| .\" |
| .\" SPDX-License-Identifier: LGPL-2.0-or-later |
| .\" |
| .TH io_uring_prep_fixed_fd_install 3 "December 8, 2023" "liburing-2.6" "liburing Manual" |
| .SH NAME |
| io_uring_prep_fixed_fd_install \- prepare fixed file fd installation request |
| .SH SYNOPSIS |
| .nf |
| .B #include <liburing.h> |
| .PP |
| .BI "void io_uring_prep_fixed_fd_install(struct io_uring_sqe *" sqe "," |
| .BI " int " fd "," |
| .BI " unsigned int " flags ");" |
| .fi |
| .SH DESCRIPTION |
| .PP |
| The |
| .BR io_uring_prep_fixed_fd_install (3) |
| helper prepares a fixed file descriptor installation. The submission queue entry |
| .I sqe |
| is setup to install the direct/fixed file descriptor |
| .I fd |
| with the specified |
| .I flags |
| file installation flags. |
| |
| One use case of direct/fixed file descriptors is to turn a regular file |
| descriptor into a direct one, reducing the overhead of any request that |
| needs to access this file. This helper provides a way to go the other way, |
| turning a direct descriptor into a regular file descriptor that can then |
| subsequently be used by regular system calls that take a normal file descriptor. |
| This can be handy if no regular file descriptor exists for this direct |
| descriptor. Either because it was instantiated directly as a fixed descriptor, |
| or because the regular file was closed with |
| .BR close (2) |
| after being turned into a direct descriptor. |
| |
| Upon successful return of this request, both a normal and fixed file descriptor |
| exists for the same file. Either one of them may be used to access the file. |
| Either one of them may be closed without affecting the other one. |
| |
| .I flags |
| may be either zero, or set to |
| .B IORING_FIXED_FD_NO_CLOEXEC |
| to indicate that the new regular file descriptor should not be closed during |
| exec. By default, |
| .B O_CLOEXEC |
| will be set on the new descriptor otherwise. Setting this field to anything but |
| those two values will result in the request being failed with |
| .B -EINVAL |
| in the CQE |
| .I res |
| field. |
| |
| .SH RETURN VALUE |
| None |
| .SH ERRORS |
| The CQE |
| .I res |
| field will contain the result of the operation, which in this case will be the |
| value of the new regular file descriptor. In case of failure, a negative value |
| is returned. |
| .SH SEE ALSO |
| .BR io_uring_get_sqe (3), |
| .BR io_uring_submit (3), |
| .BR io_uring_register_files (3), |
| .BR io_uring_unregister_files (3), |
| .BR io_uring_prep_close_direct (3), |
| .BR io_uring_prep_openat_direct (3) |
