closefrom: Close all file descriptors above a certain value.

[ccan] / ccan / closefrom / closefrom.h

diff --git a/ccan/closefrom/closefrom.h b/ccan/closefrom/closefrom.h
new file mode 100644 (file)
index 0000000..790a5ba
--- /dev/null
+++ b/ccan/closefrom/closefrom.h
@@ -0,0 +1,81 @@
+/* CC0 license (public domain) - see LICENSE file for details */
+#ifndef CCAN_CLOSEFROM_H
+#define CCAN_CLOSEFROM_H
+#include "config.h"
+#include <stdbool.h>
+
+#if HAVE_CLOSEFROM
+/* BSD.  */
+#include <unistd.h>
+/* Solaris.  */
+#include <stdlib.h>
+
+static inline
+bool closefrom_may_be_slow(void)
+{
+       return 0;
+}
+
+static inline
+void closefrom_limit(unsigned int limit)
+{
+}
+
+#else /* !HAVE_CLOSEFROM */
+
+/**
+ * closefrom - Close all open file descriptors, starting
+ * at fromfd onwards.
+ * @fromfd: the first fd to close; it and all higher file descriptors
+ * will be closed.
+ *
+ * This is not multithread-safe: other threads in the same process
+ * may or may not open new file descriptors in parallel to this call.
+ * However, the expected use-case is that this will be called in a
+ * child process just after fork(), meaning the child process is still
+ * single-threaded.
+ */
+void closefrom_(int fromfd);
+/* In case the standard library has it, but declared in some
+ * *other* header we do not know of yet, we use closefrom_ in
+ * the actual name the linker sees.
+ */
+#define closefrom closefrom_
+
+/**
+ * closefrom_may_be_slow - check if the closefrom() function could
+ * potentially take a long time.
+ *
+ * The return value is true if closefrom() is emulated by
+ * looping from fromfd to sysconf(_SC_OPEN_MAX), which can be
+ * very large (possibly even INT_MAX on some systems).
+ * If so, you might want to use setrlimit to limit _SC_OPEN_MAX.
+ * If this returns false, then closefrom is efficient and you do not
+ * need to limit the number of file descriptors.
+ *
+ * You can use closefrom_limit to perform the limiting based on
+ * closefrom_may_be_slow.
+ * This API is exposed in case you want to output to debug logs or
+ * something similar.
+ */
+bool closefrom_may_be_slow(void);
+
+/**
+ * closefrom_limit - If closefrom_may_be_slow(), lower the limit on
+ * the number of file descriptors we keep open, to prevent closefrom
+ * from being *too* slow.
+ * @limit: 0 to use a reasonable default of 4096, or non-zero for the
+ * limit you prefer.
+ *
+ * This function does nothing if closefrom_may_be_slow() return false.
+ *
+ * This function only *lowers* the limit from the hard limit set by
+ * root before running this program.
+ * If the limit is higher than the hard limit, then the hard limit is
+ * respected.
+ */
+void closefrom_limit(unsigned int limit);
+
+#endif /* !HAVE_CLOSEFROM */
+
+#endif /* CCAN_CLOSEFROM_H */