67918b32ab
NAME
fallocate - preallocate or deallocate space to a file
SYNOPSIS
fallocate [-c|-p|-z] [-o offset] -l length [-n] filename
fallocate -d [-o offset] [-l length] filename
DESCRIPTION
fallocate is used to manipulate the allocated disk space for a file,
either to deallocate or preallocate it. For filesystems which support
the fallocate system call, preallocation is done quickly by allocating
blocks and marking them as uninitialized, requiring no IO to the data
blocks. This is much faster than creating a file by filling it with
zeroes.
function old new delta
fallocate_main - 179 +179
applet_names 2597 2606 +9
applet_main 1504 1508 +4
applet_suid 94 95 +1
applet_install_loc 188 189 +1
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
105 lines
4.0 KiB
C
105 lines
4.0 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* Copyright (C) 2017 Denys Vlasenko <vda.linux@googlemail.com>
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*
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* Licensed under GPLv2, see file LICENSE in this source tree.
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*/
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//config:config FALLOCATE
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//config: bool "fallocate"
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//config: default y
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//config: help
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//config: Preallocate space for files.
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//applet:IF_FALLOCATE(APPLET(fallocate, BB_DIR_USR_BIN, BB_SUID_DROP))
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//kbuild:lib-$(CONFIG_FALLOCATE) += fallocate.o
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//usage:#define fallocate_trivial_usage
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//usage: "[-o OFS] -l LEN FILE"
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// fallocate [-c|-p|-z] [-n] [-o OFS] -l LEN FILE
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// fallocate -d [-o OFS] [-l LEN] FILE
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//usage:#define fallocate_full_usage "\n\n"
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//usage: "Preallocate space for FILE\n"
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// "\n -c Remove range"
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// "\n -p Make hole"
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// "\n -z Zero and allocate range"
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// "\n -d Convert zeros to holes"
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// "\n -n Keep size"
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//usage: "\n -o OFS Offset of range"
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//usage: "\n -l LEN Length of range"
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//Upstream options:
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//The options --collapse-range, --dig-holes, --punch-hole and --zero-range
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//are mutually exclusive.
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//-c, --collapse-range
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// Removes a byte range from a file, without leaving a hole. The byte range
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// to be collapsed starts at offset and continues for length bytes.
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// At the completion of the operation, the contents of the file starting
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// at the location offset+length will be appended at the location offset,
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// and the file will be length bytes smaller. The option --keep-size may
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// not be specified for the collapse-range operation.
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//-d, --dig-holes
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// Detect and dig holes. This makes the file sparse in-place, without using
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// extra disk space. The minimum size of the hole depends on filesystem I/O
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// block size (usually 4096 bytes). Also,
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//-l, --length length
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// Specifies the length of the range, in bytes.
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//-n, --keep-size
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// Do not modify the apparent length of the file. This may effectively
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// allocate blocks past EOF, which can be removed with a truncate.
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//-o, --offset offset
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// Specifies the beginning offset of the range, in bytes.
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//-p, --punch-hole
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// Deallocates space (i.e., creates a hole) in the byte range starting
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// at offset and continuing for length bytes. Within the specified range,
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// partial filesystem blocks are zeroed, and whole
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// filesystem blocks are removed from the file. After a successful call,
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// subsequent reads from this range will return zeroes. This option may not
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// be specified at the same time as the
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// --zero-range option. Also, when using this option, --keep-size is implied.
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//-z, --zero-range
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// Zeroes space in the byte range starting at offset and continuing for
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// length bytes. Within the specified range, blocks are preallocated for
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// the regions that span the holes in the file. After
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// a successful call, subsequent reads from this range will return zeroes.
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// Zeroing is done within the filesystem preferably by converting the range
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// into unwritten extents. This approach means that the specified range
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// will not be physically zeroed out on the device (except for partial
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// blocks at the either end of the range), and I/O is (otherwise) required
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// only to update metadata.
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// Option --keep-size can be specified to prevent file length modification.
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#include "libbb.h"
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int fallocate_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int fallocate_main(int argc UNUSED_PARAM, char **argv)
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{
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const char *str_l;
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const char *str_o = "0";
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off_t ofs, len;
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unsigned opts;
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int fd;
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/* exactly one non-option arg */
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opt_complementary = "=1";
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opts = getopt32(argv, "l:o:", &str_l, &str_o);
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if (!(opts & 1))
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bb_show_usage();
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ofs = xatoull_sfx(str_o, kmg_i_suffixes);
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len = xatoull_sfx(str_l, kmg_i_suffixes);
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argv += optind;
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fd = xopen3(*argv, O_RDWR | O_CREAT, 0666);
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/* posix_fallocate has unusual method of returning error */
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/* maybe use Linux-specific fallocate(int fd, int mode, off_t offset, off_t len) instead? */
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if ((errno = posix_fallocate(fd, ofs, len)) != 0)
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bb_perror_msg_and_die("fallocate '%s'", *argv);
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/* util-linux also performs fsync(fd); */
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return EXIT_SUCCESS;
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}
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