closefrom(3C)

NAME

     closefrom, fdwalk - close or iterate over open file descrip-
     tors

SYNOPSIS

     #include <stdlib.h>

     void closefrom(int  lowfd);

     int fdwalk(int (*func)(void *, int), void *cd);

DESCRIPTION

     The closefrom() function calls close(2)  on  all  open  file
     descriptors greater than or equal to lowfd.

     The effect of closefrom(lowfd) is the same as the code

     #include <sys/resource.h>
     struct rlimit rl;
     int i;

     getrlimit(RLIMIT_NOFILE, &rl);
     for (i = lowfd; i < rl.rlim_max; i++)
          (void) close(i);

     except that close() is called only on file descriptors  that
     are  actually  open,  not  on every possible file descriptor
     greater than or equal to lowfd, and close() is  also  called
     on  any  open  file  descriptors  greater  than  or equal to
     rl.rlim_max (and lowfd), should any exist.

     The fdwalk() function first makes a list  of  all  currently
     open  file descriptors. Then for each file descriptor in the
     list, it calls  the  user-defined  function,  func(cd,  fd),
     passing  it  the  pointer  to the callback data, cd, and the
     value of the file descriptor from the list, fd.  The list is
     processed  in  file  descriptor  value order, lowest numeric
     value first.

     If func() returns a non-zero value, the iteration  over  the
     list  is  terminated and fdwalk() returns the non-zero value
     returned by func().  Otherwise,  fdwalk()  returns  0  after
     having called func() for every file descriptor in the list.

     The fdwalk() function can be used for  fine-grained  control
     over  the  closing  of  file  descriptors.  For example, the
     closefrom() function can be implemented as:

     static int
     close_func(void *lowfdp, int fd)
     {
          if (fd >= *(int *)lowfdp)
               (void) close(fd);
          return (0);
     }

     void
     closefrom(int lowfd)
     {
          (void) fdwalk(close_func, &lowfd);
     }

     The fdwalk() function can then be used to count  the  number
     of open files in the process.

RETURN VALUES

     No return value is defined for closefrom(). If close() fails
     for  any  of the open file descriptors, the error is ignored
     and the file  descriptors  whose  close()  operation  failed
     might remain open on return from closefrom().

     The fdwalk() function returns the return value of  the  last
     call  to  the  callback  function  func(), or 0 if func() is
     never called (no open files).

ERRORS

     No errors are defined. The closefrom()  and  fdwalk()  func-
     tions do not set errno but errno can be set by close() or by
     another function called by the callback function, func().

FILES

          /proc/self/fd
                directory (list of open files)

USAGE

     The act of closing all open file descriptors should be  per-
     formed  only as the first action of a daemon process.  Clos-
     ing file descriptors  that  are  in  use  elsewhere  in  the
     current process normally leads to disastrous results.

ATTRIBUTES

     See attributes(5)  for descriptions of the following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | Unsafe                      |
    |_____________________________|_____________________________|

SEE ALSO

     close(2), getrlimit(2), proc(4), attributes(5)