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/* One of many ways to emulate flock() on top of real (good) POSIX locks. */
#ident "$RH: flock.c,v 1.2 2000/08/23 17:07:00 nalin Exp $"
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
int flock(int fd, int operation)
{
int i, cmd;
struct flock l = {0, 0, 0, 0, 0};
if(operation & LOCK_NB) {
cmd = F_SETLK;
} else {
cmd = F_SETLKW;
}
l.l_whence = SEEK_SET;
switch(operation & (~LOCK_NB)) {
case LOCK_EX:
l.l_type = F_WRLCK;
i = fcntl(fd, cmd, &l);
if(i == -1) {
if((errno == EAGAIN) || (errno == EACCES)) {
errno = EWOULDBLOCK;
}
}
break;
case LOCK_SH:
l.l_type = F_RDLCK;
i = fcntl(fd, cmd, &l);
if(i == -1) {
if((errno == EAGAIN) || (errno == EACCES)) {
errno = EWOULDBLOCK;
}
}
break;
case LOCK_UN:
l.l_type = F_UNLCK;
i = fcntl(fd, cmd, &l);
if(i == -1) {
if((errno == EAGAIN) || (errno == EACCES)) {
errno = EWOULDBLOCK;
}
}
break;
default:
i = -1;
errno = EINVAL;
break;
}
return i;
}
#ifdef FLOCK_EMULATE_IS_MAIN
int main(int argc, char **argv)
{
int fd = open(argv[1], O_WRONLY);
flock(fd, LOCK_EX);
return 0;
}
#endif
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