linux系统编程之struct flock 结构体
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该结构是在lock.h文件中定义。
lock.h File
功能
定义一些文件的锁的选项
Description
The flock structure in the /usr/include/sys/flock.h file, which describes a lock, contains the following fields:
l_type | Describes the type of lock. If the value of the Command parameter to the fcntl subroutine is F_SETLK orF_SETLKW, the l_type field indicates the type of lock to be created. Possible values are:
If the value of the Command parameter to the fcntl subroutine is F_GETLK, the l_type field describes an existing lock. Possible values are:
|
l_whence | Defines the starting offset. The value of this field indicates the point from which the relative offset, the l_startfield, is measured. Possible values are:
These values are defined in the unistd.h file. |
l_start | Defines the relative offset in bytes, measured from the starting point in the l_whence field. |
l_len | Specifies the number of consecutive bytes to be locked. |
l_sysid | Contains the ID of the node that already has a lock placed on the area defined by the fcntl subroutine. This field is returned only when the value of the Command parameter is F_GETLK. |
l_pid | Contains the ID of a process that already has a lock placed on the area defined by the fcntl subroutine. This field is returned only when the value of the Command parameter is F_GETLK. |
l_vfs
| Specifies the file system type of the node identified in the l_sysid field. |
看一下示例吧!
int
waldirlock(Wal *w)
{
int r;
int fd;
struct flock lk;
char path[PATH_MAX];
r = snprintf(path, PATH_MAX, "%s/lock", w->dir);
if (r > PATH_MAX) {
twarnx("path too long: %s/lock", w->dir);
return 0;
}
fd = open(path, O_WRONLY|O_CREAT, 0600);
if (fd == -1) {
twarn("open");
return 0;
}
lk.l_type = F_WRLCK;
lk.l_whence = SEEK_SET;
lk.l_start = 0;
lk.l_len = 0;
r = fcntl(fd, F_SETLK, &lk);
if (r) {
twarn("fcntl");
return 0;
}
// intentionally leak fd, since we never want to close it
// and we'll never need it again
return 1;
}
struct flock 作为fcntl函数的第三个参数,使用F_SETLK,设置了其参数。
更多文章,欢迎访问:http://blog.csdn.net/wallwind
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