1POSIX_FALLOCATE(3)         Linux Programmer's Manual        POSIX_FALLOCATE(3)
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NAME

6       posix_fallocate - allocate file space
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SYNOPSIS

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

19       The function posix_fallocate() ensures that disk space is allocated for
20       the file referred to by the file descriptor fd for  the  bytes  in  the
21       range  starting  at  offset and continuing for len bytes.  After a suc‐
22       cessful call to posix_fallocate(), subsequent writes to  bytes  in  the
23       specified  range  are  guaranteed  not  to fail because of lack of disk
24       space.
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26       If the size of the file is less  than  offset+len,  then  the  file  is
27       increased to this size; otherwise the file size is left unchanged.
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RETURN VALUE

30       posix_fallocate()  returns zero on success, or an error number on fail‐
31       ure.  Note that errno is not set.
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ERRORS

34       EBADF  fd is not a valid file descriptor, or is not opened for writing.
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36       EFBIG  offset+len exceeds the maximum file size.
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38       EINTR  A signal was caught during execution.
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40       EINVAL offset was less than 0, or len was less than or equal to  0,  or
41              the underlying filesystem does not support the operation.
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43       ENODEV fd does not refer to a regular file.
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45       ENOSPC There is not enough space left on the device containing the file
46              referred to by fd.
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48       ESPIPE fd refers to a pipe.
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VERSIONS

51       posix_fallocate() is available since glibc 2.1.94.
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ATTRIBUTES

54       For  an  explanation  of  the  terms  used   in   this   section,   see
55       attributes(7).
56
57       ┌──────────────────┬───────────────┬─────────────────────────┐
58Interface         Attribute     Value                   
59       ├──────────────────┼───────────────┼─────────────────────────┤
60posix_fallocate() │ Thread safety │ MT-Safe (but see NOTES) │
61       └──────────────────┴───────────────┴─────────────────────────┘

CONFORMING TO

63       POSIX.1-2001.
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65       POSIX.1-2008 says that an implementation shall give the EINVAL error if
66       len was 0, or offset was less than 0.  POSIX.1-2001 says that an imple‐
67       mentation  shall give the EINVAL error if len is less than 0, or offset
68       was less than 0, and may give the error if len equals zero.
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NOTES

71       In the glibc implementation, posix_fallocate() is implemented using the
72       fallocate(2) system call, which is MT-safe.  If the underlying filesys‐
73       tem does not support fallocate(2), then the operation is emulated  with
74       the following caveats:
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76       * The emulation is inefficient.
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78       * There is a race condition where concurrent writes from another thread
79         or process could be overwritten with null bytes.
80
81       * There is a race condition where concurrent  file  size  increases  by
82         another  thread  or  process  could  result  in  a file whose size is
83         smaller than expected.
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85       * If fd has been opened with the O_APPEND or O_WRONLY flags, the  func‐
86         tion fails with the error EBADF.
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88       In  general,  the emulation is not MT-safe.  On Linux, applications may
89       use fallocate(2) if they cannot tolerate  the  emulation  caveats.   In
90       general, this is only recommended if the application plans to terminate
91       the operation if EOPNOTSUPP  is  returned,  otherwise  the  application
92       itself  will need to implement a fallback with all the same problems as
93       the emulation provided by glibc.
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SEE ALSO

96       fallocate(1), fallocate(2), lseek(2), posix_fadvise(2)
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COLOPHON

99       This page is part of release 5.02 of the Linux  man-pages  project.   A
100       description  of  the project, information about reporting bugs, and the
101       latest    version    of    this    page,    can     be     found     at
102       https://www.kernel.org/doc/man-pages/.
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106GNU                               2017-09-15                POSIX_FALLOCATE(3)
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