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d7e6e3100a
Use Linux fallocate system call to preallocate storage for the target file in copy_file backends based on sendfile and copy_file_range. These backends are only used when the file size is known beforehand, and preallocating storage allows to reduce filesystem fragmentation and get an early error if there's not enough free space on the target filesystem. Preallocation is only done as an optimization/hint. On filesystems that do not support it we continue the data copying process as before. This is why we aren't using posix_fallocate, because glibc contains an emulation path that is used when the filesystem doesn't support the functionality. We don't want this emulation, as it would effectively double the amount of written data.
20 lines
514 B
C++
20 lines
514 B
C++
// Copyright 2024 Andrey Semashev
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// Distributed under the Boost Software License, Version 1.0.
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// See http://www.boost.org/LICENSE_1_0.txt
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// See library home page at http://www.boost.org/libs/filesystem
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#include "platform_config.hpp"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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int main()
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{
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int fd = open("file.txt", O_CREAT | O_TRUNC | O_WRONLY, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH);
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int err = fallocate(fd, FALLOC_FL_KEEP_SIZE, 0, 4096);
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return err != 0;
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}
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