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/* Copyright (C) 2000-2024 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
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdint.h>
#include <sys/fcntl.h>
#include <sys/stat.h>
#include <sys/statfs.h>
/* Reserve storage for the data of the file associated with FD. This
emulation is far from perfect, but the kernel cannot do not much
better for network file systems, either. */
int
posix_fallocate (int fd, __off_t offset, __off_t len)
{
struct __stat64_t64 st;
if (offset < 0 || len < 0)
return EINVAL;
/* Perform overflow check. The outer cast relies on a GCC
extension. */
if ((__off_t) ((uint64_t) offset + (uint64_t) len) < 0)
return EFBIG;
/* pwrite below will not do the right thing in O_APPEND mode. */
{
int flags = __fcntl (fd, F_GETFL, 0);
if (flags < 0 || (flags & O_APPEND) != 0)
return EBADF;
}
/* We have to make sure that this is really a regular file. */
if (__fstat64_time64 (fd, &st) != 0)
return EBADF;
if (S_ISFIFO (st.st_mode))
return ESPIPE;
if (! S_ISREG (st.st_mode))
return ENODEV;
if (len == 0)
{
/* This is racy, but there is no good way to satisfy a
zero-length allocation request. */
if (st.st_size < offset)
{
int ret = __ftruncate (fd, offset);
if (ret != 0)
ret = errno;
return ret;
}
return 0;
}
/* Minimize data transfer for network file systems, by issuing
single-byte write requests spaced by the file system block size.
(Most local file systems have fallocate support, so this fallback
code is not used there.) */
unsigned increment;
{
struct statfs64 f;
if (__fstatfs64 (fd, &f) != 0)
return errno;
if (f.f_bsize == 0)
increment = 512;
else if (f.f_bsize < 4096)
increment = f.f_bsize;
else
/* NFS does not propagate the block size of the underlying
storage and may report a much larger value which would still
leave holes after the loop below, so we cap the increment at
4096. */
increment = 4096;
}
/* Write a null byte to every block. This is racy; we currently
lack a better option. Compare-and-swap against a file mapping
might additional local races, but requires interposition of a
signal handler to catch SIGBUS. */
for (offset += (len - 1) % increment; len > 0; offset += increment)
{
len -= increment;
if (offset < st.st_size)
{
unsigned char c;
ssize_t rsize = __pread (fd, &c, 1, offset);
if (rsize < 0)
return errno;
/* If there is a non-zero byte, the block must have been
allocated already. */
else if (rsize == 1 && c != 0)
continue;
}
if (__pwrite (fd, "", 1, offset) != 1)
return errno;
}
return 0;
}
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