403ec61cbb
man page and POSIX: posix_fadvise(2) returns an error number on failure. Reported by: jilles MFC after: 1 week
140 lines
4.1 KiB
Groff
140 lines
4.1 KiB
Groff
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.\" @(#)madvise.2 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd October 3, 2015
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.Dt POSIX_FADVISE 2
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.Os
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.Sh NAME
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.Nm posix_fadvise
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.Nd give advice about use of file data
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In fcntl.h
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.Ft int
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.Fn posix_fadvise "int fd" "off_t offset" "off_t len" "int advice"
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.Sh DESCRIPTION
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The
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.Fn posix_fadvise
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system call
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allows a process to describe to the system its data access behavior for an
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open file descriptor
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.Fa fd .
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The advice covers the data starting at offset
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.Fa offset
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and continuing for
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.Fa len
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bytes.
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If
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.Fa len
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is zero,
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all data from
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.Fa offset
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to the end of the file is covered.
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.Pp
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The behavior is specified by the
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.Fa advice
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parameter and may be one of:
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.Bl -tag -width POSIX_FADV_SEQUENTIAL
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.It Dv POSIX_FADV_NORMAL
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Tells the system to revert to the default data access behavior.
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.It Dv POSIX_FADV_RANDOM
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Is a hint that file data will be accessed randomly,
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and prefetching is likely not advantageous.
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.It Dv POSIX_FADV_SEQUENTIAL
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Tells the system that file data will be accessed sequentially.
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This currently does nothing as the default behavior uses heuristics to
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detect sequential behavior.
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.It Dv POSIX_FADV_WILLNEED
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Tells the system that the specified data will be accessed in the near future.
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The system may initiate an asynchronous read of the data if it is not already
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present in memory.
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.It Dv POSIX_FADV_DONTNEED
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Tells the system that the specified data will not be accessed in the near
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future.
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The system may decrease the in-memory priority of clean data within the
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specified range and future access to this data may require a read operation.
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.It Dv POSIX_FADV_NOREUSE
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Tells the system that the specified data will only be accessed once and
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then not reused.
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The system may decrease the in-memory priority of data once it has been
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read or written.
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Future access to this data may require a read operation.
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.El
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.Sh RETURN VALUES
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If successful,
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.Fn posix_fadvise
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returns zero.
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It returns an error on failure, without setting
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.Va errno .
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.Sh ERRORS
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Possible failure conditions:
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.Bl -tag -width Er
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.It Bq Er EBADF
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The
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.Fa fd
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argument is not a valid file descriptor.
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.It Bq Er EINVAL
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The
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.Fa advice
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argument is not valid.
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.It Bq Er EINVAL
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The
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.Fa offset
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or
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.Fa len
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arguments are negative,
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or
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.Fa offset
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+
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.Fa len
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is greater than the maximum file size.
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.It Bq Er ENODEV
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The
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.Fa fd
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argument does not refer to a regular file.
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.It Bq Er ESPIPE
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The
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.Fa fd
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argument is associated with a pipe or FIFO.
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.El
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.Sh SEE ALSO
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.Xr madvise 2
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.Sh STANDARDS
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The
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.Fn posix_fadvise
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interface conforms to
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.St -p1003.1-2001 .
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.Sh HISTORY
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The
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.Fn posix_fadvise
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system call first appeared in
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.Fx 9.1 .
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