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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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F_GET_RW_HINT(2const) F_GET_RW_HINT(2const)
F_GET_RW_HINT, F_SET_RW_HINT, F_GET_FILE_RW_HINT,
F_SET_FILE_RW_HINT - get/set file read/write hints
Standard C library (libc, -lc)
#include <fcntl.h>
int fcntl(int fd, F_GET_RW_HINT, uint64_t *arg);
int fcntl(int fd, F_SET_RW_HINT, uint64_t *arg);
int fcntl(int fd, F_GET_FILE_RW_HINT, uint64_t *arg);
int fcntl(int fd, F_GET_FILE_RW_HINT, uint64_t *arg);
Write lifetime hints can be used to inform the kernel about the
relative expected lifetime of writes on a given inode or via a
particular open file description. (See open(2) for an explanation
of open file descriptions.) In this context, the term "write
lifetime" means the expected time the data will live on media,
before being overwritten or erased.
An application may use the different hint values specified below
to separate writes into different write classes, so that multiple
users or applications running on a single storage back-end can
aggregate their I/O patterns in a consistent manner. However,
there are no functional semantics implied by these flags, and
different I/O classes can use the write lifetime hints in
arbitrary ways, so long as the hints are used consistently.
The following operations can be applied to the file descriptor,
fd:
F_GET_RW_HINT
Returns the value of the read/write hint associated with
the underlying inode referred to by fd.
F_SET_RW_HINT
Sets the read/write hint value associated with the
underlying inode referred to by fd. This hint persists
until either it is explicitly modified or the underlying
filesystem is unmounted.
F_GET_FILE_RW_HINT
Returns the value of the read/write hint associated with
the open file description referred to by fd.
F_SET_FILE_RW_HINT
Sets the read/write hint value associated with the open
file description referred to by fd.
If an open file description has not been assigned a read/write
hint, then it shall use the value assigned to the inode, if any.
The following read/write hints are supported:
RWH_WRITE_LIFE_NOT_SET
No specific hint has been set. This is the default value.
RWH_WRITE_LIFE_NONE
No specific write lifetime is associated with this file or
inode.
RWH_WRITE_LIFE_SHORT
Data written to this inode or via this open file
description is expected to have a short lifetime.
RWH_WRITE_LIFE_MEDIUM
Data written to this inode or via this open file
description is expected to have a lifetime longer than data
written with RWH_WRITE_LIFE_SHORT.
RWH_WRITE_LIFE_LONG
Data written to this inode or via this open file
description is expected to have a lifetime longer than data
written with RWH_WRITE_LIFE_MEDIUM.
RWH_WRITE_LIFE_EXTREME
Data written to this inode or via this open file
description is expected to have a lifetime longer than data
written with RWH_WRITE_LIFE_LONG.
All the write-specific hints are relative to each other, and no
individual absolute meaning should be attributed to them.
Zero.
On error, -1 is returned, and errno is set to indicate the error.
See fcntl(2).
Linux.
Linux 4.13.
fcntl(2)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-07-20 F_GET_RW_HINT(2const)
Pages that refer to this page: fcntl(2)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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