busybox/util-linux/fallocate.c
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   1/* vi: set sw=4 ts=4: */
   2/*
   3 * Copyright (C) 2017 Denys Vlasenko <vda.linux@googlemail.com>
   4 *
   5 * Licensed under GPLv2, see file LICENSE in this source tree.
   6 */
   7//config:config FALLOCATE
   8//config:       bool "fallocate (5 kb)"
   9//config:       default y
  10//config:       help
  11//config:       Preallocate space for files.
  12
  13//applet:IF_FALLOCATE(APPLET(fallocate, BB_DIR_USR_BIN, BB_SUID_DROP))
  14
  15//kbuild:lib-$(CONFIG_FALLOCATE) += fallocate.o
  16
  17//usage:#define fallocate_trivial_usage
  18//usage:       "[-o OFS] -l LEN FILE"
  19//              fallocate [-c|-p|-z] [-n] [-o OFS] -l LEN FILE
  20//              fallocate -d [-o OFS] [-l LEN] FILE
  21//usage:#define fallocate_full_usage "\n\n"
  22//usage:        "Preallocate space for FILE\n"
  23//           "\n        -c      Remove range"
  24//           "\n        -p      Make hole"
  25//           "\n        -z      Zero and allocate range"
  26//           "\n        -d      Convert zeros to holes"
  27//           "\n        -n      Keep size"
  28//usage:     "\n        -o OFS  Offset of range"
  29//usage:     "\n        -l LEN  Length of range"
  30
  31//Upstream options:
  32//The options --collapse-range, --dig-holes, --punch-hole and --zero-range
  33//are mutually exclusive.
  34//-c, --collapse-range
  35//    Removes a byte range from a file, without leaving a hole. The byte range
  36//    to be collapsed starts at offset and continues for length bytes.
  37//    At the completion of the operation, the contents of the file starting
  38//    at the location offset+length will be appended at the location offset,
  39//    and the file will be length bytes smaller. The option --keep-size may
  40//    not be specified for the collapse-range operation.
  41//-d, --dig-holes
  42//    Detect and dig holes. This makes the file sparse in-place, without using
  43//    extra disk space. The minimum size of the hole depends on filesystem I/O
  44//    block size (usually 4096 bytes). Also,
  45//-l, --length length
  46//    Specifies the length of the range, in bytes.
  47//-n, --keep-size
  48//    Do not modify the apparent length of the file. This may effectively
  49//    allocate blocks past EOF, which can be removed with a truncate.
  50//-o, --offset offset
  51//    Specifies the beginning offset of the range, in bytes.
  52//-p, --punch-hole
  53//    Deallocates space (i.e., creates a hole) in the byte range starting
  54//    at offset and continuing for length bytes. Within the specified range,
  55//    partial filesystem blocks are zeroed, and whole
  56//    filesystem blocks are removed from the file. After a successful call,
  57//    subsequent reads from this range will return zeroes. This option may not
  58//    be specified at the same time as the
  59//    --zero-range option. Also, when using this option, --keep-size is implied.
  60//-z, --zero-range
  61//    Zeroes space in the byte range starting at offset and continuing for
  62//    length bytes. Within the specified range, blocks are preallocated for
  63//    the regions that span the holes in the file. After
  64//    a successful call, subsequent reads from this range will return zeroes.
  65//    Zeroing is done within the filesystem preferably by converting the range
  66//    into unwritten extents. This approach means that the specified range
  67//    will not be physically zeroed out on the device (except for partial
  68//    blocks at the either end of the range), and I/O is (otherwise) required
  69//    only to update metadata.
  70//    Option --keep-size can be specified to prevent file length modification.
  71
  72#include "libbb.h"
  73
  74int fallocate_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  75int fallocate_main(int argc UNUSED_PARAM, char **argv)
  76{
  77        const char *str_l;
  78        const char *str_o = "0";
  79        off_t ofs, len;
  80        unsigned opts;
  81        int fd;
  82
  83        /* exactly one non-option arg */
  84        opts = getopt32(argv, "^" "l:o:" "\0" "=1", &str_l, &str_o);
  85        if (!(opts & 1))
  86                bb_show_usage();
  87
  88        ofs = xatoull_sfx(str_o, kmg_i_suffixes);
  89        len = xatoull_sfx(str_l, kmg_i_suffixes);
  90
  91        argv += optind;
  92        fd = xopen3(*argv, O_RDWR | O_CREAT, 0666);
  93
  94        /* posix_fallocate has unusual method of returning error */
  95        /* maybe use Linux-specific fallocate(int fd, int mode, off_t offset, off_t len) instead? */
  96        if ((errno = posix_fallocate(fd, ofs, len)) != 0)
  97                bb_perror_msg_and_die("fallocate '%s'", *argv);
  98
  99        /* util-linux also performs fsync(fd); */
 100
 101        return EXIT_SUCCESS;
 102}
 103