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123 lines
3.4 KiB
C
123 lines
3.4 KiB
C
/* Copyright (C) 2000-2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <errno.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <stdint.h>
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#include <sys/fcntl.h>
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#include <sys/stat.h>
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#include <sys/statfs.h>
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/* Reserve storage for the data of the file associated with FD. This
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emulation is far from perfect, but the kernel cannot do not much
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better for network file systems, either. */
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int
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posix_fallocate (int fd, __off_t offset, __off_t len)
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{
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struct __stat64_t64 st;
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if (offset < 0 || len < 0)
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return EINVAL;
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/* Perform overflow check. The outer cast relies on a GCC
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extension. */
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if ((__off_t) ((uint64_t) offset + (uint64_t) len) < 0)
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return EFBIG;
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/* pwrite below will not do the right thing in O_APPEND mode. */
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{
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int flags = __fcntl (fd, F_GETFL, 0);
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if (flags < 0 || (flags & O_APPEND) != 0)
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return EBADF;
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}
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/* We have to make sure that this is really a regular file. */
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if (__fstat64_time64 (fd, &st) != 0)
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return EBADF;
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if (S_ISFIFO (st.st_mode))
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return ESPIPE;
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if (! S_ISREG (st.st_mode))
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return ENODEV;
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if (len == 0)
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{
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/* This is racy, but there is no good way to satisfy a
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zero-length allocation request. */
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if (st.st_size < offset)
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{
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int ret = __ftruncate (fd, offset);
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if (ret != 0)
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ret = errno;
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return ret;
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}
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return 0;
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}
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/* Minimize data transfer for network file systems, by issuing
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single-byte write requests spaced by the file system block size.
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(Most local file systems have fallocate support, so this fallback
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code is not used there.) */
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unsigned increment;
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{
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struct statfs64 f;
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if (__fstatfs64 (fd, &f) != 0)
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return errno;
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if (f.f_bsize == 0)
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increment = 512;
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else if (f.f_bsize < 4096)
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increment = f.f_bsize;
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else
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/* NFS does not propagate the block size of the underlying
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storage and may report a much larger value which would still
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leave holes after the loop below, so we cap the increment at
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4096. */
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increment = 4096;
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}
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/* Write a null byte to every block. This is racy; we currently
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lack a better option. Compare-and-swap against a file mapping
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might additional local races, but requires interposition of a
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signal handler to catch SIGBUS. */
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for (offset += (len - 1) % increment; len > 0; offset += increment)
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{
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len -= increment;
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if (offset < st.st_size)
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{
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unsigned char c;
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ssize_t rsize = __pread (fd, &c, 1, offset);
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if (rsize < 0)
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return errno;
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/* If there is a non-zero byte, the block must have been
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allocated already. */
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else if (rsize == 1 && c != 0)
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continue;
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}
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if (__pwrite (fd, "", 1, offset) != 1)
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return errno;
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}
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return 0;
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}
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