lk.l_whence=SEEK_SET;是什么意思？

lk.l_whence=SEEK_SET;是什么意思？

这是flock的l_whence域吧？它用来表示l_start的含义，如果l_whence=SEEK_SET，那么l_start就是从文件头开始计算的偏移值。

如果l_whence=SEEK_CUR，那么l_start表示从文件当前指针位置开始计算的偏移值，如果为SEEK_END，那么l_start为从文件尾向前移动的偏移值。

The l_whence, l_start, and l_len fields of this structure specify the
range of bytes we wish to lock. l_start is the starting offset for the
lock, and is interpreted relative to either: the start of the file (if
l_whence is SEEK_SET); the current file offset (if l_whence is
SEEK_CUR); or the end of the file (if l_whence is SEEK_END). In the
final two cases, l_start can be a negative number provided the offset
does not lie before the start of the file.

linux下可用man 2 fcntl看到这些内容。