arm_fadvise64_64(2)

1POSIX_FADVISE(2)           Linux Programmer's Manual          POSIX_FADVISE(2)
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NAME

6       posix_fadvise - predeclare an access pattern for file data
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SYNOPSIS

9       #include <fcntl.h>
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11       int posix_fadvise(int fd, off_t offset, off_t len, int advice);
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13   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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15       posix_fadvise():
16           _XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L
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DESCRIPTION

19       Programs  can  use  posix_fadvise()  to announce an intention to access
20       file data in a specific pattern in the future, thus allowing the kernel
21       to perform appropriate optimizations.
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23       The  advice  applies to a (not necessarily existent) region starting at
24       offset and extending for len bytes (or until the end of the file if len
25       is 0) within the file referred to by fd.  The advice is not binding; it
26       merely constitutes an expectation on behalf of the application.
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28       Permissible values for advice include:
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30       POSIX_FADV_NORMAL
31              Indicates that the application has no advice to give  about  its
32              access  pattern  for  the specified data.  If no advice is given
33              for an open file, this is the default assumption.
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35       POSIX_FADV_SEQUENTIAL
36              The application expects to access  the  specified  data  sequen‐
37              tially (with lower offsets read before higher ones).
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39       POSIX_FADV_RANDOM
40              The specified data will be accessed in random order.
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42       POSIX_FADV_NOREUSE
43              The specified data will be accessed only once.
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45       POSIX_FADV_WILLNEED
46              The specified data will be accessed in the near future.
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48       POSIX_FADV_DONTNEED
49              The specified data will not be accessed in the near future.
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RETURN VALUE

52       On success, zero is returned.  On error, an error number is returned.
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ERRORS

55       EBADF  The fd argument was not a valid file descriptor.
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57       EINVAL An invalid value was specified for advice.
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59       ESPIPE The  specified file descriptor refers to a pipe or FIFO.  (Linux
60              actually returns EINVAL in this case.)
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VERSIONS

63       Kernel support first appeared in Linux 2.5.60;  the  underlying  system
64       call  is  called  fadvise64().  Library support has been provided since
65       glibc version 2.2, via the wrapper function posix_fadvise().
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CONFORMING TO

68       POSIX.1-2001.  Note that the type of the len argument was changed  from
69       size_t to off_t in POSIX.1-2003 TC1.
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NOTES

72       Under Linux, POSIX_FADV_NORMAL sets the readahead window to the default
73       size for the backing device; POSIX_FADV_SEQUENTIAL doubles  this  size,
74       and  POSIX_FADV_RANDOM disables file readahead entirely.  These changes
75       affect the entire file, not just the specified region (but  other  open
76       file handles to the same file are unaffected).
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78       POSIX_FADV_WILLNEED  initiates  a  nonblocking  read  of  the specified
79       region into the page cache.  The amount of data read may  be  decreased
80       by  the kernel depending on virtual memory load.  (A few megabytes will
81       usually be fully satisfied, and more is rarely useful.)
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83       In kernels before 2.6.18, POSIX_FADV_NOREUSE had the same semantics  as
84       POSIX_FADV_WILLNEED.   This  was  probably  a bug; since kernel 2.6.18,
85       this flag is a no-op.
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87       POSIX_FADV_DONTNEED attempts to free cached pages associated  with  the
88       specified  region.   This is useful, for example, while streaming large
89       files.  A program may periodically request the kernel  to  free  cached
90       data  that  has already been used, so that more useful cached pages are
91       not discarded instead.
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93       Pages that have not yet been written out will be unaffected, so if  the
94       application  wishes to guarantee that pages will be released, it should
95       call fsync(2) or fdatasync(2) first.
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97   Architecture-specific variants
98       Some architectures require 64-bit arguments to be aligned in a suitable
99       pair  of registers (see syscall(2) for further detail).  On such archi‐
100       tectures, the call signature of posix_fadvise() shown in  the  SYNOPSIS
101       would  force  a register to be wasted as padding between the fd and len
102       arguments.  Therefore, these architectures define a version of the sys‐
103       tem call that orders the arguments suitably, but otherwise is otherwise
104       exactly the same as posix_fadvise().
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106       For example, since Linux 2.6.14, ARM has the following system call:
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108           long arm_fadvise64_64(int fd, int advice,
109                                 loff_t offset, loff_t len);
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111       These architecture-specific details are generally hidden from  applica‐
112       tions  by the glibc posix_fadvise() wrapper function, which invokes the
113       appropriate architecture-specific system call.
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BUGS

116       In kernels before 2.6.6, if len was  specified  as  0,  then  this  was
117       interpreted  literally  as  "zero  bytes",  rather than as meaning "all
118       bytes through to the end of the file".
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COLOPHON

124       This page is part of release 3.53 of the Linux  man-pages  project.   A
125       description  of  the project, and information about reporting bugs, can
126       be found at http://www.kernel.org/doc/man-pages/.
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130Linux                             2013-04-01                  POSIX_FADVISE(2)