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#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <sys/file.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#define DEBUG_OUTPUT 1
int flock(int fd, int operation)
{
int nonblock;
int open_mode;
struct flock lock;
int req;
int err;
nonblock = operation&LOCK_NB;
operation &= ~LOCK_NB;
if(operation==LOCK_SH)
lock.l_type = F_RDLCK;
else if(operation==LOCK_EX)
lock.l_type = F_WRLCK;
else if(operation==LOCK_UN)
lock.l_type = F_UNLCK;
else
{
errno = EINVAL;
return -1;
}
lock.l_whence = SEEK_SET;
lock.l_start = 0;
lock.l_len = 0;
lock.l_pid = 0;
open_mode = fcntl(fd, F_GETFL, NULL)&O_ACCMODE;
if(lock.l_type==F_RDLCK && open_mode==O_WRONLY)
lock.l_type = F_WRLCK;
else if(lock.l_type==F_WRLCK && open_mode==O_RDONLY)
lock.l_type = F_RDLCK;
req = (nonblock ? F_OFD_SETLK : F_OFD_SETLKW);
#ifdef DEBUG_OUTPUT
const char *op_str = NULL;
if(operation==LOCK_SH)
op_str = "LOCK_SH";
else if(operation==LOCK_EX)
op_str = "LOCK_EX";
else if(operation==LOCK_UN)
op_str = "LOCK_UN";
const char *req_str = NULL;
if(req==F_OFD_SETLK)
req_str = "F_OFD_SETLK";
else if(req==F_OFD_SETLKW)
req_str = "F_OFD_SETLKW";
const char *type_str = NULL;
if(lock.l_type==F_RDLCK)
type_str = "F_RDLCK";
else if(lock.l_type==F_WRLCK)
type_str = "F_WRLCK";
else if(lock.l_type==F_UNLCK)
type_str = "F_UNLCK";
const char *mode_str = NULL;
if(open_mode==O_RDONLY)
mode_str = "O_RDONLY";
else if(open_mode==O_WRONLY)
mode_str = "O_WRONLY";
else if(open_mode==O_RDWR)
mode_str = "O_RDWR";
printf("Translated flock(%d, %s%s) with open mode %s to fcntl(%d, %s, { .l_type = %s })\n", fd, op_str, (nonblock ? "|LOCK_NB" : ""), mode_str, fd, req_str, type_str);
#endif
err = fcntl(fd, req, &lock);
if(err<0)
{
err = errno;
#ifdef DEBUG_OUTPUT
printf("Error %d (%s)\n", err, strerror(errno));
#endif
if(nonblock && (err==EAGAIN || err==EACCES))
errno = EWOULDBLOCK;
return -1;
}
return 0;
}
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