volmgt_acquire(3VOLMGTVolume Management Library Functiovolmgt_acquire(3VOLMGT)NAMEvolmgt_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 spec‐
ified 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 path‐
name (for example, /vol/dsk/unnamed_floppy).
If Volume Management is not running, volmgt_acquire() requires call‐
ers 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 reserva‐
tion 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 reser‐
vation.
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 TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │ MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOvold(1M), free(3C), malloc(3C), volmgt_release(3VOLMGT), attributes(5)NOTES
When returning a string through err, volmgt_acquire() allocates a mem‐
ory 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.
SunOS 5.10 11 Dec 1996 volmgt_acquire(3VOLMGT)
