[Devel] Re: [user-cr][PATCH 2/2] Add --mount-pty option to mount new devpts

[Oren Laadan]

Serge E. Hallyn wrote:
> Quoting Oren Laadan (orenl at cs.columbia.edu):
>> Based on Serge Hallyn's patch:
>>
>>   "Trivial patch, and I'm not sure whether we want this or want to do
>>   it this way.  But it saves me having to do it during my restart.sh
>>   wrapper shell-script."
>>
>> Make sure that the old /dev/pts is un-mounted prior to the mount of
>> the new one.
>>
>> Signed-off-by: Oren Laadan <orenl at cs.columbia.edu>
>> ---
>>  restart.c |   40 ++++++++++++++++++++++++++++++++++++++++
>>  1 files changed, 40 insertions(+), 0 deletions(-)
>>
>> diff --git a/restart.c b/restart.c
>> index f42b456..e3c4a5c 100644
>> --- a/restart.c
>> +++ b/restart.c
>> @@ -53,6 +53,7 @@ static char usage_str[] =
>>  "     --signal=SIG       send SIG to root task on SIGINT (default: SIGKILL\n"
>>  "                        to container root, SIGINT otherwise)\n"
>>  "     --mntns            restart under a private mounts namespace\n"
>> +"     --mount-pty        start in a new devpts namespace to supprt ptys\n"
>>  "  -w,--wait             wait for root task to termiate (default)\n"
>>  "     --show-status      show exit status of root task (implies -w)\n"
>>  "     --copy-status      imitate exit status of root task (implies -w)\n"
>> @@ -275,6 +276,7 @@ int global_send_sigint = -1;
>>  int global_sent_sigint;
>>
>>  static int ckpt_remount_proc(void);
>> +static int ckpt_remount_devpts(void);
>>
>>  static int ckpt_build_tree(struct ckpt_ctx *ctx);
>>  static int ckpt_init_tree(struct ckpt_ctx *ctx);
>> @@ -342,6 +344,7 @@ struct args {
>>  	char *root;
>>  	int wait;
>>  	int mntns;
>> +	int mnt_pty;
>>  	int show_status;
>>  	int copy_status;
>>  	char *freezer;
>> @@ -432,6 +435,7 @@ static void parse_args(struct args *args, int argc, char *argv[])
>>  		{ "debug",	no_argument,		NULL, 'd' },
>>  		{ "warn-pidzero",	no_argument,	NULL, 9 },
>>  		{ "fail-pidzero",	no_argument,	NULL, 10 },
>> +		{ "mount-pty",	no_argument,		NULL, 12 },
>>  		{ NULL,		0,			NULL, 0 }
>>  	};
>>  	static char optc[] = "hdvkpPwWF:r:i:l:";
>> @@ -538,6 +542,9 @@ static void parse_args(struct args *args, int argc, char *argv[])
>>  		case 11:
>>  			args->mntns = 1;
>>  			break;
>> +		case 12:
>> +			args->mnt_pty = 1;
>> +			break;
>>  		default:
>>  			usage(usage_str);
>>  		}
>> @@ -591,6 +598,9 @@ static void parse_args(struct args *args, int argc, char *argv[])
>>  		printf("Invalid used of both -l/--logfile and --logfile-fd\n");
>>  		exit(1);
>>  	}
>> +
>> +	if (args->mnt_pty)
>> +		args->mntns = 1;
>>  }
>>
>>  static void report_exit_status(int status, char *str, int debug)
>> @@ -785,6 +795,10 @@ int main(int argc, char *argv[])
>>  		exit(1);
>>  	}
>>
>> +	/* remount /dev/pts ? */
>> +	if (args.mnt_pty && ckpt_remount_devpts() < 0)
>> +		exit(1);
>> +
>>  	/* self-restart ends here: */
>>  	if (args.self) {
>>  		restart(getpid(), STDIN_FILENO, RESTART_TASKSELF, args.logfd);
>> @@ -916,6 +930,32 @@ static int ckpt_collect_child(struct ckpt_ctx *ctx)
>>  	return ckpt_parse_status(status, mimic, verbose);
>>  }
>>
>> +static int ckpt_remount_devpts(void)
>> +{
>> +	struct stat ptystat;
>> +
>> +	/* make sure /dev/ptmx is a link else we'll just break */
>> +	if (lstat("/dev/ptmx", &ptystat) < 0) {
>> +		perror("stat /dev/ptmx");
>> +		return -1;
>> +	}
>> +	if ((ptystat.st_mode & S_IFMT) != S_IFLNK) {
>> +		ckpt_err("Error: /dev/ptmx must be a link to /dev/pts/ptmx\n");
>> +		return -1;
>> +	}
>> +
>> +	if (umount2("/dev/pts", MNT_DETACH) < 0) {
>> +		perror("umount -l /dev/pts");
>> +		return -1;
>> +	}
>> +	if (mount("pts", "/dev/pts", "devpts", 0, "newinstance") < 0) {
> 
> How about making that
> 
> 	if (mount("pts", "/dev/pts", "devpts", 0, "ptmxmode=666,newinstance")
> 				< 0) {
> 
> (or take that as another arg if you must)?  Otherwise restarting
> non-root-owned tasks not only ends up with tasks not able to create
> a new terminal, but you can't externally fix that since the mount
> is private...

Ok. And also either umount() won't fail by default.

Oren.

> 
>> +		perror("mount -t devpts -o newinstance");
>> +		return -1;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>  static int ckpt_close_files(void)
>>  {
>>  	char fdpath[64], *endp;
>> -- 
>> 1.6.3.3
> 
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