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/*
** This file implements a simple command-line utility that shows all of the
** Posix Advisory Locks on a file.
**
** Usage:
**
** showlocks FILENAME
**
** To compile: gcc -o showlocks showlocks.c
*/
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
/* This utility only looks for locks in the first 2 billion bytes */
#define MX_LCK 2147483647
/*
** Print all locks on the inode of "fd" that occur in between
** lwr and upr, inclusive.
*/
static int showLocksInRange(int fd, off_t lwr, off_t upr){
int cnt = 0;
struct flock x;
struct lockRange {
off_t lwr;
off_t upr;
} *aPending = 0;
int nAlloc = 1;
int nPending = 0;
int nDone = 0;
nPending = 1;
aPending = malloc( sizeof(aPending[0]) );
if( aPending==0 ){
fprintf(stderr, "out of memory\n");
exit(1);
}
aPending[0].lwr = lwr;
aPending[0].upr = upr;
for(nDone=0; nDone<nPending; nDone++){
lwr = aPending[nDone].lwr;
upr = aPending[nDone].upr;
if( lwr>=upr ) continue;
x.l_type = F_WRLCK;
x.l_whence = SEEK_SET;
x.l_start = lwr;
x.l_len = upr - lwr;
fcntl(fd, F_GETLK, &x);
if( x.l_type==F_UNLCK ) continue;
printf("start: %-12d len: %-5d pid: %-5d type: %s\n",
(int)x.l_start, (int)x.l_len,
x.l_pid, x.l_type==F_WRLCK ? "WRLCK" : "RDLCK");
cnt++;
if( nPending+2 > nAlloc ){
nAlloc = nAlloc*2 + 2;
aPending = realloc(aPending, sizeof(aPending[0])*nAlloc );
}
if( aPending==0 ){
fprintf(stderr, "unable to realloc for %d bytes\n",
(int)sizeof(aPending[0])*(nPending+2));
exit(1);
}
if( lwr<x.l_start ){
aPending[nPending].lwr = lwr;
aPending[nPending].upr = x.l_start;
nPending++;
}
if( x.l_start+x.l_len<=upr ){
aPending[nPending].lwr = x.l_start + x.l_len;
aPending[nPending].upr = upr;
nPending++;
}
}
free(aPending);
return cnt;
}
int main(int argc, char **argv){
int fd;
int cnt;
if( argc!=2 ){
fprintf(stderr, "Usage: %s FILENAME\n", argv[0]);
return 1;
}
fd = open(argv[1], O_RDWR, 0);
if( fd<0 ){
fprintf(stderr, "%s: cannot open %s\n", argv[0], argv[1]);
return 1;
}
cnt = showLocksInRange(fd, 0, MX_LCK);
if( cnt==0 ) printf("no locks\n");
close(fd);
return 0;
}
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