Not able to lock the port

smartgupta · 02-10-2009, 03:22 AM

Hi,
I am working with Sun-Solaris 9 and in our application I need to connect the UPS with Serial port,after that I need to monitor it..but before stating communication,It should lock that port,To check it,first i am trying to make sure the lock directory exists and I am able to find it(/var/lock) but not able to lock the port and getting the error message from there---

LOCKDIR=/var/lock in PosixDevLock.c at 53
LOCKDIR=/var/lock in PosixDevLock.c at 57
Error message in PosixDevLock.c at 58
lckStatus value==>2

I am trying to lock the port using the function lock from other file and getting the value in lckStatus variable.

Code:


	Quote:
	
	
		
			
				
int ChkPortIO (const char* portName)
{

printf(" \n Inside ChkPortIO at 82 ...........");
printf("\n 1..JNI_OK value==>%d",JNI_OK);

struct termio pmode;            /* modem device attributes */
int portID;                    /* modem port file descriptor */
int lckStatus;

lckStatus = lock(portName);

    if (lckStatus)
        {
       printf("\n lckStatus value==>%d",lckStatus);
       return(lckStatus);
       }

/* Open what is hopefully a real serial port. We use readonly access here
// just in case it is something else like a file.
 */

portID = open(portName, O_RDONLY | O_NDELAY | O_NOCTTY);

printf("\n Just before portID value==>%d",portID);

      if (portID < 0)
       {
        printf("\n Inside PortID error no ==>%d",errno);
       ulock(portName);
       return (errno);
       }

this lock function try to lock the port but during this i am not able to lock the port

Code:


	Quote:
	
	
		
			
				
int lock(const char *line)
{
#ifdef POSIX_DEV_LOCK
int     mypid, rempid, i;
int rc = -1;
char tmpname[MAXPATHLEN], lckname[MAXPATHLEN], prodName[MAXPATHLEN];
char *p;
FILE *f;

/* First of all, make sure the lock directory exists. */
#ifdef AIX
   if (mkdir(LOCKDIR, S_IWUSR) != 0)
#else
  printf("\n LOCKDIR=%s in PosixDevLock.c at 53",LOCKDIR);

   if (mkdir(LOCKDIR, S_IWUSR) != 0)
#else
  printf("\n LOCKDIR=%s in PosixDevLock.c at 53",LOCKDIR);

   if (mkdir(LOCKDIR) != 0)
#endif
    {
 printf("\n LOCKDIR=%s in PosixDevLock.c at 57",LOCKDIR);
   if (errno != EEXIST)
    {
 printf("\n Error message in PosixDevLock.c at 58 \n");
                         return(errno);
    }
/* Get only the	text after the last '/'. */
p = strrchr(line, '/');
if (p == NULL)
{
    p = (char*)line;
}
else
{
 p++;
printf("\n value of p in 71 => %d",p);
}

/* Create a temporary lock file. */
mypid = getpid();
sprintf(tmpname, "%s%d", LCKTMP, mypid);

printf("\n mypid at 78==>> %d",mypid);
printf("\n tmpname at 79==> %s",tmpname);
	
f = fopen(tmpname, "w");
   if (f == NULL)
     {
	return(errno);
     }
 }

It should not go to the if statement(if (mkdir(LOCKDIR) != 0))but it is and returns the error no.-2 means(no such file or directory )...

Quote:

Inside ChkPortIO at 82 ...........
1..JNI_OK value==>0
LOCKDIR=/var/lock in PosixDevLock.c at 53
LOCKDIR=/var/lock in PosixDevLock.c at 57
Error message in PosixDevLock.c at 58
lckStatus value==>2

Please help me to resolve it...
Thanks in advance

dwhitney67 · 02-10-2009, 07:31 AM

Can you please reformat the code that you have posted within CODE blocks. Highlight your code, then select the # symbol shown above the edit box.

I'm really confused with the #ifdef/#else in your code; there appears that there is not a closing #endif for one of the #ifdef statements.

If you need to print the line number in your printf() statements, use __LINE__. Try to avoid hard-coding the line number.

Why are you attempting to create the directory /var/lock? Does it not already exist on your system? If for some chance it doesn't, does your application have the appropriate run-time privilege to create the directory?

P.S. Use strerror() to yield the text-version of the error code returned by the system library calls. It might help in your analysis of your code.

Code:

#include <string.h>
#include <errno.h>
#include <stdio.h>

...

int status = mkdir(...);

if (status != 0)
{
  printf("Received error at line %d: %s\n", __LINE__, strerror(errno));
}

smartgupta · 02-10-2009, 08:18 AM

Thanks a lot...I will do it.

Yes,it already exist but for precaution,we are doing it..
Yes,application have the appropriate run-time privilege to create it..

but I am able to understand why It is going to if statement even directory is there and also don't have anything.

Quote:

/var
# ls -l lock
total 0
# cd lock
# pwd
/var/lock
# ls -l
total 0
# pwd
/var/lock

So it should not go to the if statement..So can you please help me to understand it and help me to resolve it...

Thanks in advance

dwhitney67 · 02-10-2009, 08:24 AM

If the directory /var/lock already exists, and you attempt a mkdir(), you can expect it to fail. See the man-page for mkdir() (man 2 mkdir).

Code:

int rtn = mkdir("/var/lock", 01777);

if (rtn != 0)
{
  if (errno != EEXIST)
  {
    // grave error...
  }
}

P.S. You really should consider employing the use of stat() before attempting a mkdir(). If you are attempting to create a directory, and either a file or a directory with the same name already exists, mkdir() will not provide the details of this information. stat() on the other hand, can provide the details.

P.S.S. I experimented a little with mkdir(); be aware of your environment's umask setting. It will have an affect on the permissions set on the folder if it is created. Under Linux, the mode given is ANDed with the umask value and ANDed with 01777. This means apart from the permission bits, only the S_ISVTX mode bit is seen.