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volmgt_acquire

Section: Volume Management Library Functions (3VOLMGT)
Updated: 11 Dec 1996
Index Return to Main Contents
 

NAME

volmgt_acquire - reserve removable media device  

SYNOPSIS

cc [ flag ... ] file ... -lvolmgt [ library ... ]
#include <sys/types.h>

#include <volmgt.h>

int volmgt_acquire(char *dev, char *id, int ovr, char **err, pid_t *pidp);  

DESCRIPTION

The volmgt_acquire() routine reserves the removable media device specified as dev. volmgt_acquire() operates in two different modes, depending on whether or not Volume Management is running. See vold(1M).

If Volume Management is running, volmgt_acquire() attempts to reserve the removable media device specified as dev. Specify dev as either a symbolic device name (for example, floppy0) or a physical device pathname (for example, /vol/dsk/unnamed_floppy).

If Volume Management is not running, volmgt_acquire() requires callers to specify a physical device pathname for dev. Specifying dev as a symbolic device name is not acceptable. In this mode, volmgt_acquire() relies entirely on the major and minor numbers of the device to determine whether or not the device is reserved.

If dev is free, volmgt_acquire() updates the internal device reservation database with the caller's process id (pid) and the specified id string.

If dev is reserved by another process, the reservation attempt fails and volmgt_acquire():

• sets errno to EBUSY

• fills the caller's id value in the array pointed to by err

• fills in the pid to which the pointer pidp points with the pid of the process which holds the reservation, if the supplied pidp is non-zero

If the override ovr is non-zero, the call overrides the device reservation.  

RETURN VALUES

Upon successful completion, volmgt_acquire() returns a non-zero value.

Upon failure, volmgt_acquire() returns 0. If the return value is 0, and errno is set to EBUSY, the address pointed to by err contains the string that was specified as id (when the device was reserved by the process holding the reservation).  

ERRORS

The volmgt_acquire() routine fails if one or more of the following are true:

EINVAL One of the specified arguments is invalid or missing.

EBUSY dev is already reserved by another process (and ovr was not set to a non-zero value)

 

EXAMPLES

Example 1: Using volmgt_acquire()

In the following example, Volume Management is running and the first floppy drive is reserved, accessed and released.

#include <volmgt.h>
char *errp;
if (!volmgt_acquire("floppy0", "FileMgr", 0, NULL,
    &errp, NULL)) {
        /* handle error case */
        ...
}
/* floppy acquired - now access it */
if (!volmgt_release("floppy0")) {
        /* handle error case */
        ...
}

Example 2: Using volmgt_acquire() To Override A Lock On Another Process

The following example shows how callers can override a lock on another process using volmgt_acquire().

char *errp, buf[20];
int override = 0;
pid_t pid;
if (!volmgt_acquire("floppy0", "FileMgr", 0, &errp,
    &pid)) {
      if (errno == EBUSY) {
             (void) printf("override %s (pid=%ld)?\n",
                errp, pid); {
             (void) fgets(buf, 20, stdin);
             if (buf[0] == 'y') {
                   override++;
             }
       } else {
             /* handle other errors */
             ...
       }
}
if (override) {
      if (!volmgt_acquire("floppy0", "FileMgr", 1,
          &errp, NULL)) {
             /* really give up this time! */
             ...
      }
}

 

ATTRIBUTES

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPEATTRIBUTE VALUE
MT-Level MT-Safe

 

SEE ALSO

vold(1M), free(3C), malloc(3C), volmgt_release(3VOLMGT), attributes(5)  

NOTES

When returning a string through err, volmgt_acquire() allocates a memory area using malloc(3C). Use free(3C) to release the memory area when no longer needed.

The ovr argument is intended to allow callers to override the current device reservation. It is assumed that the calling application has determined that the current reservation can safely be cleared. See EXAMPLES.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
ERRORS
EXAMPLES
ATTRIBUTES
SEE ALSO
NOTES

This document was created by man2html, using the manual pages.
Time: 02:38:46 GMT, October 02, 2010