04277e02d7
* All files with FSF copyright notices: Update copyright dates using scripts/update-copyrights. * locale/programs/charmap-kw.h: Regenerated. * locale/programs/locfile-kw.h: Likewise.
88 lines
3.1 KiB
C
88 lines
3.1 KiB
C
/* Test for file system hole support.
|
|
Copyright (C) 2018-2019 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#include <stdbool.h>
|
|
#include <support.h>
|
|
#include <support/check.h>
|
|
#include <sys/stat.h>
|
|
#include <xunistd.h>
|
|
|
|
int
|
|
support_descriptor_supports_holes (int fd)
|
|
{
|
|
enum
|
|
{
|
|
/* Write offset for the enlarged file. This value is arbitrary
|
|
and hopefully large enough to trigger the creation of holes.
|
|
We cannot use the file system block size as a reference here
|
|
because it is incorrect for network file systems. */
|
|
write_offset = 16 * 1024 * 1024,
|
|
|
|
/* Our write may add this number of additional blocks (see
|
|
block_limit below). */
|
|
block_headroom = 8,
|
|
};
|
|
|
|
struct stat64 st;
|
|
xfstat (fd, &st);
|
|
if (!S_ISREG (st.st_mode))
|
|
FAIL_EXIT1 ("descriptor %d does not refer to a regular file", fd);
|
|
if (st.st_size != 0)
|
|
FAIL_EXIT1 ("descriptor %d does not refer to an empty file", fd);
|
|
if (st.st_blocks > block_headroom)
|
|
FAIL_EXIT1 ("descriptor %d refers to a pre-allocated file (%lld blocks)",
|
|
fd, (long long int) st.st_blocks);
|
|
|
|
/* Write a single byte at the start of the file to compute the block
|
|
usage for a single byte. */
|
|
xlseek (fd, 0, SEEK_SET);
|
|
char b = '@';
|
|
xwrite (fd, &b, 1);
|
|
/* Attempt to bypass delayed allocation. */
|
|
TEST_COMPARE (fsync (fd), 0);
|
|
xfstat (fd, &st);
|
|
|
|
/* This limit is arbitrary. The file system needs to store
|
|
somewhere that data exists at the write offset, and this may
|
|
moderately increase the number of blocks used by the file, in
|
|
proportion to the initial block count, but not in proportion to
|
|
the write offset. */
|
|
unsigned long long int block_limit = 2 * st.st_blocks + block_headroom;
|
|
|
|
/* Write a single byte at 16 megabytes. */
|
|
xlseek (fd, write_offset, SEEK_SET);
|
|
xwrite (fd, &b, 1);
|
|
/* Attempt to bypass delayed allocation. */
|
|
TEST_COMPARE (fsync (fd), 0);
|
|
xfstat (fd, &st);
|
|
bool supports_holes = st.st_blocks <= block_limit;
|
|
|
|
/* Also check that extending the file does not fill up holes. */
|
|
xftruncate (fd, 2 * write_offset);
|
|
/* Attempt to bypass delayed allocation. */
|
|
TEST_COMPARE (fsync (fd), 0);
|
|
xfstat (fd, &st);
|
|
supports_holes = supports_holes && st.st_blocks <= block_limit;
|
|
|
|
/* Return to a zero-length file. */
|
|
xftruncate (fd, 0);
|
|
xlseek (fd, 0, SEEK_SET);
|
|
|
|
return supports_holes;
|
|
}
|