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fcntl.2: Various improvements to Jens Axboe's patch 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2017-08-26 03:23:40 +02:00
parent 86b626e520
commit b9ef608731
1 changed files with 28 additions and 13 deletions
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41
man2/fcntl.2
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@ -1496,30 +1496,41 @@ all outstanding writes will be discarded.
.\"
.SS File read/write hints
Write lifetime hints can be used to inform the kernel about the relative
expected lifetime of writes on a given inode or file, that is,
expected lifetime of writes on a given inode or
via a particular open file description.
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 this interface for separating writes into different write classes,
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 they are used consistently.
.\" FIXME What are "I/O classes"?
in arbitrary ways, so long as the hints are used consistently.
.PP
The following operations can be applied to the file descriptor,
.IR fd :
.TP
.BR F_GET_RW_HINT " (\fIuint64_t\fP; since Linux 4.13)"
Returns the value of the read/write hint associated with the underlying inode
for the file descriptor.
referred to by
.IR fd .
.TP
.BR F_SET_RW_HINT " (\fIuint64_t\fP; since Linux 4.13)"
Sets the read/write hint value associated with the underlying inode for the
file descriptor.
Sets the read/write hint value associated with the
underlying inode referred to by
.IR fd .
.TP
.BR F_GET_FILE_RW_HINT " (\fIuint64_t\fP; since Linux 4.13)"
Returns the value of the read/write hint associated with the file descriptor.
Returns the value of the read/write hint associated with
the open file description referred to by
.IR fd .
.TP
.BR F_SET_FILE_RW_HINT " (\fIuint64_t\fP; since Linux 4.13)"
Sets the read/write hint value associated with the file descriptor.
Sets the read/write hint value associated with the open file description
referred to by the file descriptor.
.PP
If a given file descriptor has not been assigned a read/write hint, then it
shall use the value assigned to the inode, if any.
@ -1534,20 +1545,24 @@ This is the default value.
No specific write lifetime is associated with this file or inode.
.TP
.BR RWH_WRITE_LIFE_SHORT
Data written to this file or inode is expected to have a short lifetime.
Data written to this inode or via this open file description
is expected to have a short lifetime.
.TP
.BR RWH_WRITE_LIFE_MEDIUM
Data written to this file or inode is expected to have a lifetime longer than
Data written to this inode or via this open file description
is expected to have a lifetime longer than
data written with
.BR RWH_WRITE_LIFE_SHORT .
.TP
.BR RWH_WRITE_LIFE_LONG
Data written to this file or inode is expected to have a lifetime longer than
Data written to this inode or via this open file description
is expected to have a lifetime longer than
data written with
.BR RWH_WRITE_LIFE_MEDIUM .
.TP
.BR RWH_WRITE_LIFE_EXTREME
Data written to this file or inode is expected to have a lifetime longer than
Data written to this inode or via this open file description
is expected to have a lifetime longer than
data written with
.BR RWH_WRITE_LIFE_LONG .
.PP