This stackoverflow answer[1] by mark4o might also be of interest: > While portable, closing all file descriptors up to > sysconf(_SC_OPEN_MAX) is not reliable, because on most systems this > call returns the current file descriptor soft limit, which could have > been lowered below the highest used file descriptor. Another issue is > that on many systems sysconf(_SC_OPEN_MAX) may return INT_MAX, which > can cause this approach to be unacceptably slow. Unfortunately, there > is no reliable, portable alternative that does not involve iterating > over every possible non-negative int file descriptor. > > Although not portable, most operating systems in common use today > provide one or more of the following solutions to this problem: > 1. A library function to close all file descriptors >= fd. This is the > simplest solution for the common case of closing all file > descriptors, although it cannot be used for much else. To close all > file descriptors except for a certain set, dup2 can be used to move > them to the low end beforehand, and to move them back afterward if > necessary. > + closefrom(fd) (Solaris 9 or later, NetBSD 3.0 or later, > OpenBSD 3.5 or later.) > + fcntl(fd, F_CLOSEM, 0) (AIX, IRIX, NetBSD) > 2. A library function to provide the maximum file descriptor currently > in use by the process. To close all file descriptors above a > certain number, either close all of them up to this maximum, or > continually get and close the highest file descriptor in a loop > until the low bound is reached. Which is more efficient depends on > the file descriptor density. > + fcntl(0, F_MAXFD) (NetBSD) > + pstat_getproc(&ps, sizeof(struct pst_status), (size_t)0, > (int)getpid()) > Returns information about the process, including the highest > file descriptor currently open in ps.pst_highestfd. (HP-UX) > 3. A directory containing an entry for each open file descriptor. This > is the most flexible approach as it allows for closing all file > descriptors, finding the highest file descriptor, or doing just > about anything else on every open file descriptor, even those of > another process (on most systems). However this can be more > complicated than the other approaches for the common uses. Also, it > can fail for a variety of reasons such as proc/fdescfs not mounted, > a chroot environment, or no file descriptors available to open the > directory (process or system limit). Therefore use of this approach > is often combined with a fallback mechanism. [2]Example (OpenSSH), > [3]another example (glib). > + /proc/pid/fd/ or /proc/self/fd/ (Linux, Solaris, AIX, Cygwin, > NetBSD) (AIX does not support "self".) > + /dev/fd/ (FreeBSD, Darwin) > It can be difficult to handle all corner cases reliably with this > approach. For example consider the situation where all file > descriptors >= fd are to be closed, but all file descriptors < fd > are used, the current process resource limit is fd, and there are > file descriptors >= fd in use. Because the process resource limit > has been reached the directory cannot be opened. If closing every > file descriptor from fd through the resource limit or > sysconf(_SC_OPEN_MAX) is used as a fallback, nothing will be > closed.
[1] http://stackoverflow.com/questions/899038/getting-the-highest-allocated-file-descriptor/918469#918469 [2] http://anoncvs.mindrot.org/index.cgi/openssh/openbsd-compat/bsd-closefrom.c?view=markup [3] http://git.gnome.org/cgit/glib/tree/gio/libasyncns/asyncns.c?h=2.21.0#n205 _______________________________________________ rsyslog mailing list http://lists.adiscon.net/mailman/listinfo/rsyslog http://www.rsyslog.com
