virfile: Introduce virCloseFrom()

It is handy to close all FDs from given FD to infinity. On
FreeBSD the libc even has a function for that: closefrom(). It
was ported to glibc too, but not musl. At least glibc
implementation falls back to calling:

  close_range(from, ~0U, 0);

Now that we have a wrapper for close_range() we implement
closefrom() trivially.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Kristina Hanicova <khanicov@redhat.com>

src/libvirt_private.syms

@@ -2275,6 +2275,7 @@ saferead;
 safewrite;
 safezero;
 virBuildPathInternal;
+virCloseFrom;
 virCloseRange;
 virCloseRangeInit;
 virCloseRangeIsSupported;

src/util/virfile.c

@@ -265,6 +265,27 @@ virCloseRangeIsSupported(void)
 }
 
 
+/**
+ * virCloseFrom:
+ *
+ * Closes all open file descriptors greater than or equal to @fromfd.
+ *
+ * Returns: 0 on success,
+ *         -1 on error (with errno set).
+ */
+int
+virCloseFrom(int fromfd)
+{
+#ifdef __FreeBSD__
+    /* FreeBSD has closefrom() since FreeBSD-8.0, i.e. since 2009. */
+    closefrom(fromfd);
+    return 0;
+#else /* !__FreeBSD__ */
+    return virCloseRange(fromfd, ~0U);
+#endif /* !__FreeBSD__ */
+}
+
+
 /**
  * virFileDirectFdFlag:
  *

src/util/virfile.h

@@ -64,6 +64,7 @@ static inline void virForceCloseHelper(int *fd)
 int virCloseRange(unsigned int from, unsigned int to);
 int virCloseRangeInit(void);
 bool virCloseRangeIsSupported(void);
+int virCloseFrom(int fromfd);
 
 /* For use on normal paths; caller must check return value,
    and failure sets errno per close. */