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F_GET_RW_HINT(2const) — Linux manual page

F_GET_RW_HINT(2const)F_GET_RW_HINT(2const)

NAME        top

       F_GET_RW_HINT, F_SET_RW_HINT, F_GET_FILE_RW_HINT,       F_SET_FILE_RW_HINT - get/set file read/write hints

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <fcntl.h>int fcntl(intfd, F_GET_RW_HINT, uint64_t *arg);int fcntl(intfd, F_SET_RW_HINT, uint64_t *arg);int fcntl(intfd, F_GET_FILE_RW_HINT, uint64_t *arg);int fcntl(intfd, F_GET_FILE_RW_HINT, uint64_t *arg);

DESCRIPTION        top

       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.  (Seeopen(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 byfd.F_SET_RW_HINT              Sets the read/write hint value associated with the              underlying inode referred to byfd.  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 byfd.F_SET_FILE_RW_HINT              Sets the read/write hint value associated with the open              file description referred to byfd.       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 withRWH_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 withRWH_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 withRWH_WRITE_LIFE_LONG.       All the write-specific hints are relative to each other, and no       individual absolute meaning should be attributed to them.

RETURN VALUE        top

       Zero.       On error, -1 is returned, anderrno is set to indicate the error.

ERRORS        top

       Seefcntl(2).

STANDARDS        top

       Linux.

HISTORY        top

       Linux 4.13.

SEE ALSO        top

fcntl(2)

COLOPHON        top

       This page is part of theman-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 isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-07-20F_GET_RW_HINT(2const)

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