On 2018/05/22 10:36, Xiong Murphy Zhou wrote:
On Mon, May 21, 2018 at 01:42:00PM +0800, Xiao Yang wrote:1) According to fcntl(2) manpage, A single process always gets F_UNLCK in the l_type field when using fcntl(F_GETLK) to acquire the existing lock set by itself because it could convert the existing lock to a new lock unconditionally. So we need another process to check if the lock exists.I used to do that, eventaully I deleted it because we don't need to check in another process in this case.
Hi Xiong, Even if the fix patch[1] has been applied, you always gets F_UNLCK without another process. According to fcntl(2) manpage: F_GETLK On input to this call, lock describes a lock we would like to place on the file. If the lock could be placed, fcntl() does not actually place it, but returns F_UNLCK in the l_type field of lock and leaves the other fields of the structure unchanged. A single process can always place a new lock on the file and return F_UNLCK because the existing lock is set by itself. [1] https://www.spinics.net/lists/linux-fsdevel/msg123144.html Thanks, Xiao Yang
Thanks, Xiong2) Remove redundant exit(0). Signed-off-by: Xiao Yang<yangx.jy@xxxxxxxxxxxxxx> --- src/t_locks_execve.c | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/src/t_locks_execve.c b/src/t_locks_execve.c index 9ad2dc3..d99d7de 100644 --- a/src/t_locks_execve.c +++ b/src/t_locks_execve.c @@ -8,6 +8,7 @@ #include<errno.h> #include<pthread.h> #include<unistd.h> +#include<sys/types.h> #include<sys/wait.h> static void err_exit(char *op, int errn) @@ -32,12 +33,24 @@ struct flock fl = { static void checklock(int fd) { - if (fcntl(fd, F_GETLK,&fl)< 0) - err_exit("getlk", errno); - if (fl.l_type == F_UNLCK) { - printf("record lock is not preserved across execve(2)\n"); - exit(1); + pid_t pid; + + pid = fork(); + if (pid< 0) + err_exit("fork", errno); + + if (!pid) { + if (fcntl(fd, F_GETLK,&fl)< 0) + err_exit("getlk", errno); + if (fl.l_type == F_UNLCK) { + printf("record lock is not preserved across execve(2)\n"); + exit(1); + } + exit(0); } + + waitpid(pid, NULL, 0); + exit(0); } @@ -52,7 +65,6 @@ int main(int argc, char **argv) if (argc == 3) { fd = atoi(argv[2]); checklock(fd); - exit(0); } fd = open(argv[1], O_WRONLY|O_CREAT, 0755); -- 1.8.3.1.
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