man2/fallocate.2

   1 .\" Copyright (c) 2007 Silicon Graphics, Inc. All Rights Reserved
   2 .\" Written by Dave Chinner <dgc@sgi.com>
   3 .\" May be distributed as per GNU General Public License version 2.
   4 .\"
   5 .TH FALLOCATE 2 2007-07-20 "Linux" "Linux Programmer's Manual"
   6 .SH NAME
   7 fallocate \- manipulate file space
   8 .SH SYNOPSIS
   9 .nf
  10 .\" FIXME . eventually this #include will probably be something
  11 .\" different when support is added in glibc.
  12 .B #include <linux/falloc.h>
  13
  14 .BI "long fallocate(int " fd ", int " mode ", loff_t " offset \
  15 ", loff_t " len ");
  16 .fi
  17 .\" FIXME . check later what feature text macros are required in glibc
  18 .SH DESCRIPTION
  19 .BR fallocate ()
  20 allows the caller to directly manipulate the allocated disk space
  21 for the file referred to by
  22 .I fd
  23 for the byte range starting at
  24 .I offset
  25 and continuing for
  26 .I len
  27 bytes.
  28
  29 The
  30 .I mode
  31 argument determines the operation to be performed on the given range.
  32 Currently only one flag is supported for
  33 .IR mode :
  34 .TP
  35 .B FALLOC_FL_KEEP_SIZE
  36 This flag allocates and initializes to zero the disk space
  37 within the range specified by
  38 .I offset
  39 and
  40 .IR len .
  41 After a successful call, subsequent writes into this range
  42 are guaranteed not to fail because of lack of disk space.
  43 Preallocating zeroed blocks beyond the end of the file
  44 is useful for optimizing append workloads.
  45 Preallocating blocks does not change
  46 the file size (as reported by
  47 .BR stat (2))
  48 even if it is less than
  49 .IR offset + len .
  50 .\"
  51 .\" Note from Amit Arora:
  52 .\" There were few more flags which were discussed, but none of
  53 .\" them have been finalized upon. Here are these flags:
  54 .\" FA_FL_DEALLOC, FA_FL_DEL_DATA, FA_FL_ERR_FREE, FA_FL_NO_MTIME,
  55 .\" FA_FL_NO_CTIME
  56 .\" All of the above flags were debated upon and we can not say
  57 .\" if any/which one of these flags will make it to the later kernels.
  58 .PP
  59 If
  60 .B FALLOC_FL_KEEP_SIZE
  61 flag is not specified in
  62 .IR mode ,
  63 the default behavior is almost same as when this flag is specified.
  64 The only difference is that on success,
  65 the file size will be changed if
  66 .I "offset + len"
  67 is greater than the file size.
  68 This default behavior closely resembles the behavior of the
  69 .BR posix_fallocate (3)
  70 library function,
  71 and is intended as a method of optimally implementing that function.
  72 .PP
  73 Because allocation is done in block size chunks,
  74 .BR fallocate ()
  75 may allocate a larger range than that which was specified.
  76 .SH RETURN VALUE
  77 .BR fallocate ()
  78 returns zero on success, or an error number on failure.
  79 Note that
  80 .\" FIXME . the library wrapper function will do the right
  81 .\" thing, returning -1 on error and setting errno.
  82 .I errno
  83 is not set.
  84 .SH ERRORS
  85 .TP
  86 .B EBADF
  87 .I fd
  88 is not a valid file descriptor, or is not opened for writing.
  89 .TP
  90 .B EFBIG
  91 .IR offset + len
  92 exceeds the maximum file size.
  93 .TP
  94 .B EINTR
  95 A signal was caught during execution.
  96 .TP
  97 .B EINVAL
  98 .I offset
  99 was less than 0, or
 100 .I len
 101 was less than or equal to 0.
 102 .TP
 103 .B EIO
 104 An I/O error occurred while reading from or writing to a file system.
 105 .TP
 106 .B ENODEV
 107 .I fd
 108 does not refer to a regular file or a directory.
 109 (If
 110 .I fd
 111 is a pipe or FIFO, a different error results.)
 112 .TP
 113 .B ENOSPC
 114 There is not enough space left on the device containing the file
 115 referred to by
 116 .IR fd .
 117 .TP
 118 .B ENOSYS
 119 The file system containing the file referred to by
 120 .I fd
 121 does not support this operation.
 122 .TP
 123 .B EOPNOTSUPP
 124 The
 125 .I mode
 126 is not supported by the file system containing the file referred to by
 127 .IR fd .
 128 .SH VERSIONS
 129 .BR fallocate ()
 130 is available on Linux since kernel 2.6.23.
 131 .SH CONFORMING TO
 132 .BR fallocate ()
 133 is Linux-specific.
 134 .SH SEE ALSO
 135 .BR ftruncate (2),
 136 .BR posix_fallocate (3),
 137 .BR posix_fadvise (3)