From 0e4690d4ef9fe55ccf6db371c826112809e162f9 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Sun, 20 Aug 2006 22:12:18 +0000
Subject: [PATCH] Michael Opdenacker contributed a readahead applet.

---
 include/applets.h     |  1 +
 include/usage.h       |  6 ++++++
 miscutils/Config.in   | 16 ++++++++++++++++
 miscutils/Makefile.in |  1 +
 miscutils/readahead.c | 36 ++++++++++++++++++++++++++++++++++++
 5 files changed, 60 insertions(+)
 create mode 100644 miscutils/readahead.c

diff --git a/include/applets.h b/include/applets.h
index a8b480b..0bb257b 100644
--- a/include/applets.h
+++ b/include/applets.h
@@ -219,6 +219,7 @@ USE_PRINTF(APPLET(printf, _BB_DIR_USR_BIN, _BB_SUID_NEVER))
 USE_PS(APPLET(ps, _BB_DIR_BIN, _BB_SUID_NEVER))
 USE_PWD(APPLET(pwd, _BB_DIR_BIN, _BB_SUID_NEVER))
 USE_RDATE(APPLET(rdate, _BB_DIR_USR_SBIN, _BB_SUID_NEVER))
+USE_READAHEAD(APPLET(readahead, _BB_DIR_USR_BIN, _BB_SUID_NEVER))
 USE_READLINK(APPLET(readlink, _BB_DIR_USR_BIN, _BB_SUID_NEVER))
 USE_READPROFILE(APPLET(readprofile, _BB_DIR_USR_SBIN, _BB_SUID_NEVER))
 USE_REALPATH(APPLET(realpath, _BB_DIR_USR_BIN, _BB_SUID_NEVER))
diff --git a/include/usage.h b/include/usage.h
index 5bc82dc..ced9f68 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -2385,6 +2385,12 @@ USE_FEATURE_MDEV_CONFIG( \
 	"\t-s\tSet the system date and time (default)\n" \
 	"\t-p\tPrint the date and time"
 
+#define readahead_trivial_usage \
+	"[FILE]..."
+#define readahead_full_usage \
+	"Preloads FILE(s) in RAM cache so that subsequent reads for those" \
+	"files do not block on disk I/O."
+
 #ifdef CONFIG_FEATURE_READLINK_FOLLOW
 #define USAGE_READLINK_FOLLOW(a) a
 #else
diff --git a/miscutils/Config.in b/miscutils/Config.in
index 4296b54..9ad3421 100644
--- a/miscutils/Config.in
+++ b/miscutils/Config.in
@@ -276,6 +276,22 @@ config CONFIG_MT
 	  to advance or rewind a tape past a specified number of archive
 	  files on the tape.
 
+config CONFIG_READAHEAD
+        bool "readahead"
+	default n
+	help
+ 	  Preload the files listed on the command line into RAM cache so that
+	  subsequent reads on these files will not block on disk I/O.
+
+	  This applet just calls the readahead(2) system call on each file.
+	  It is mainly useful in system startup scripts to preload files
+	  or executables before they are used.  When used at the right time
+	  (in particular when a CPU boundprocess is running) it can
+	  significantly speed up system startup.
+
+	  As readahead(2) blocks until each file has been read, it is best to
+	  run this applet as a background job. 
+
 config CONFIG_RUNLEVEL
         bool "runlevel"
 	default n
diff --git a/miscutils/Makefile.in b/miscutils/Makefile.in
index a0b6b72..25143c1 100644
--- a/miscutils/Makefile.in
+++ b/miscutils/Makefile.in
@@ -24,6 +24,7 @@ MISCUTILS-${CONFIG_LESS}        += less.o
 MISCUTILS-$(CONFIG_MAKEDEVS)    += makedevs.o
 MISCUTILS-$(CONFIG_MOUNTPOINT)  += mountpoint.o
 MISCUTILS-$(CONFIG_MT)          += mt.o
+MISCUTILS-$(CONFIG_READAHEAD)   += readahead.o
 MISCUTILS-$(CONFIG_RUNLEVEL)    += runlevel.o
 MISCUTILS-$(CONFIG_RX)          += rx.o
 MISCUTILS-$(CONFIG_SETSID)      += setsid.o
diff --git a/miscutils/readahead.c b/miscutils/readahead.c
new file mode 100644
index 0000000..9f1bb47
--- /dev/null
+++ b/miscutils/readahead.c
@@ -0,0 +1,36 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * readahead implementation for busybox
+ *
+ * Preloads the given files in RAM, to reduce access time.
+ * Does this by calling the readahead(2) system call.
+ *
+ * Copyright (C) 2006  Michael Opdenacker <michael@free-electrons.com>
+ *
+ * Licensed under GPLv2 or later, see file License in this tarball for details.
+ */
+
+#include "busybox.h"
+
+int readahead_main(int argc, char **argv)
+{
+	FILE *f;
+	struct stat stat_buf;
+	int retval = EXIT_SUCCESS;
+
+	if (argc == 1) bb_show_usage();
+
+	while (*++argv) {
+		if ((f = bb_wfopen(*argv, "r")) != NULL) {
+			int r, fd=fileno(f);
+			
+			xstat(*argv, &stat_buf);
+			r = readahead(fd, 0, fdlength(fd));
+			fclose(f);
+			if (r >= 0) continue;
+		}
+		retval = EXIT_FAILURE;
+	}
+
+	return retval;
+}
-- 
2.7.4