C++ pwrite() 偏移量

Question

我正在寻找一个 C++ 程序来将一些模式写入磁盘设备，但是当我尝试设置大于 0 的偏移量时遇到了问题。请参见下面的示例和代码。

谁能告诉我我做错了什么？

谢谢，

root@solaris:~/# CC simple_test.cc
root@solaris:~/# ./a.out
Insert device name, for example: /dev/rdsk/c2t600A0B800011238000001D3D45DA78A7d0s1
/dev/rdsk/c0t6000402E5000000035969F0C97324D24d0s2
iteration: 0. offset: 0
offset: 1048577
iteration: 1. offset: 1048577
WRITE operation error: 22; offset: 1048577
offset: 2097154
iteration: 2. offset: 2097154
WRITE operation error: 22; offset: 2097154
offset: 3145731
iteration: 3. offset: 3145731
WRITE operation error: 22; offset: 3145731
offset: 4194308
iteration: 4. offset: 4194308
WRITE operation error: 22; offset: 4194308
offset: 5242885
Test completed
root@solaris:~/# cat simple_test.cc
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sstream>

#define BS           1048576
using namespace std;
const char PATTERN[ ] = { 'A' };

int main(int argc, char **argv)
{
    char dev[ 100 ];
    printf( "Insert device name, for example: /dev/rdsk/c2t600A0B800011238000001D3D45DA78A7d0s1\n" );
    scanf( "%s", dev );
    int fd;
    if ( ( fd = open( dev, O_RDWR ) ) == -1 )
    {
        printf( "error opening device: %s\n", dev );
        return 1;
    }

    char* pattern = new char[ BS ];
    memset ( pattern, PATTERN[0], BS );
    int offset = 0;
    int nbytes = 0;
    for (int i=0; i<5; i++ ) {
        cout << "iteration: " << i << ". offset: " << offset << endl;
        nbytes = pwrite( fd, pattern, BS, offset );
        if ( nbytes != BS )
            printf( "WRITE operation error: %d; offset: %ld\n", errno, offset );
        offset += BS + 1;
        cout << "offset: " << offset << endl;
    }

    delete pattern;
    printf( "Test completed\n" );
    return 0;
}

Answer 1

我不确定，但是你不需要以 block 的形式写入 block 设备吗？所以你的偏移量必须是 block 大小的倍数。但是您将它增加 BS + 1。为什么是 +1？我认为如果您坚持使用 += BS，它可能会起作用。