truncate 不支持创建大小大于 2^32-1 的文件

Question

显然，我的

truncate

系统上的 gnu

x86_64

不支持创建大小 >= 8EiB（= 2^32-1 字节 = 9223372036854775807 字节）的文件。

/usr/bin/truncate: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=c45930b128536914bf8134c0f11745cbd115d34b, for GNU/Linux 3.2.0, stripped

truncate -s 9223372036854775807 file
truncate -s 8E file
truncate: Invalid number: ‘8E’: Value too large for defined data type

我假设文件大小达到 16EiB = 2^64 字节才有效，或至少 2^64 - 1 字节。

为什么我对截断实现的直觉有缺陷？

Answer 1

gnu truncate 的源代码包含以下定义：

static bool do_ftruncate (int fd, char const *fname, off_t ssize, off_t rel_mode_t rel_mode)

使用

off_t

中的

#include <sys/types.h>

类型作为文件大小。

由于它是使用

gcc

/

glibc

构建的，且

_FILE_OFFSET_BITS

设置为 64，因此

off_t

指的是

off64_t

，根据 The，“能够寻址最大 2^63 字节的文件” GNU C 库参考手册，因为它是有符号整数：

[Data Type]
off_t
This is a signed integer type used to represent file sizes. In the GNU C Library, this type is no narrower than int.
If the source is compiled with _FILE_OFFSET_BITS == 64 this type is transparently replaced by off64_t.

[Data Type]
off64_t
This type is used similar to off_t. The difference is that even on 32 bit machines, where the off_t type would have 32 bits, off64_t has 64 bits and so is able to address files up to 2^63 bytes in length.
When compiling with _FILE_OFFSET_BITS == 64 this type is available under the name off_t.