[CRIU] [PATCH 3/3] restore: Add support to flock&posix file locks' restore

[Pavel Emelyanov]

> @@ -13,3 +16,77 @@ int dump_one_file_lock(FileLockEntry *fe, const struct cr_fdset *fdset)
>  	return pb_write_one(fdset_fd(fdset, CR_FD_FILE_LOCKS),
>  			fe, PB_FILE_LOCK);
>  }
> +
> +static int restore_file_lock(FileLockEntry *fe)
> +{
> +	int ret = -1;
> +	unsigned int cmd;
> +
> +	if (fe->flag & FL_FLOCK) {
> +		if (fe->type & LOCK_MAND) {
> +			cmd = fe->type;
> +		} else if (fe->type & F_RDLCK) {
> +			cmd |= LOCK_SH;
> +		} else if (fe->type & F_WRLCK) {
> +			cmd |= LOCK_EX;
> +		} else if (fe->type & F_UNLCK) {
> +			cmd |= LOCK_UN;
> +		} else {
> +			pr_err("Unknow flock type!\n");
> +			goto err;
> +		}
> +
> +		ret = flock(fe->fd, cmd);

I believe it's not that simple. What if your app tried to lock a file and
hung on it since some other one was holding it. On restore time you will
either dead-lock here, since the lock would be busy by another restored
task or you will screw the locking up by locking the lock with wrong task.

> +		if (ret < 0) {
> +			pr_err("Can not set flock!\n");
> +			goto err;
> +		}
> +	} else if (fe->flag & FL_POSIX) {
> +		struct flock flk;
> +		memset(&flk, 0, sizeof(flk));
> +
> +		flk.l_whence = SEEK_SET;
> +		flk.l_start = fe->start;
> +		flk.l_len = fe->len;
> +		flk.l_pid = fe->pid;
> +		flk.l_type = fe->type;
> +
> +		ret = fcntl(fe->fd, F_SETLKW, &flk);
> +		if (ret < 0) {
> +			pr_err("Can not set posix lock!\n");
> +			goto err;
> +		}
> +	} else {
> +		pr_err("Unknow file lock style!\n");
> +	}
> +err:
> +	return ret;
> +}