klibc-utils: new applets: resume, nuke, minips

minips is a pure alias to ps, just in case someone needs 100% klibc-utils compat.
nuke is a primitive version of "rm -rf" without options and error checks. ~30 bytes.

resume is a tool for initramfs which resumes from a given block device.

function                                             old     new   delta
resume_main                                            -     582    +582
packed_usage                                       31640   31712     +72
nuke_main                                              -      28     +28
xstrtoull                                              -      24     +24
applet_names                                        2646    2665     +19
applet_main                                         1532    1544     +12
applet_suid                                           96      97      +1
applet_install_loc                                   192     193      +1
applet_flags                                          96      97      +1
------------------------------------------------------------------------------
(add/remove: 5/0 grow/shrink: 6/0 up/down: 740/0)             Total: 740 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 115 insertions, 0 deletions

diff --git a/klibc-utils/resume.c b/klibc-utils/resume.c
new file mode 100644
index 0000000..de142f3
--- /dev/null
+++ b/klibc-utils/resume.c
@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2017 Denys Vlasenko <vda.linux@googlemail.com>
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+//config:config RESUME
+//config:	bool "resume"
+//config:	default y
+//config:	help
+//config:	Resume from saved "suspend-to-disk" image
+
+//applet:IF_RESUME(APPLET_NOEXEC(resume, resume, BB_DIR_BIN, BB_SUID_DROP, resume))
+
+//kbuild:lib-$(CONFIG_RESUME) += resume.o
+
+#include "libbb.h"
+
+/* This is a NOEXEC applet. Be very careful! */
+
+/* name_to_dev_t() in klibc-utils supports extended device name formats,
+ * apart from the usual case where /dev/NAME already exists.
+ *
+ * - device number in hexadecimal represents itself (in dev_t layout).
+ * - device number in major:minor decimal represents itself.
+ * - if block device (or partition) with this name is found in sysfs.
+ * - if /dev/ prefix is not given, it is assumed.
+ *
+ * klibc-utils also recognizes these, but they don't work
+ * for "resume" tool purposes (thus we don't support them (yet?)):
+ * - /dev/nfs
+ * - /dev/ram (alias to /dev/ram0)
+ * - /dev/mtd
+ */
+static dev_t name_to_dev_t(const char *devname)
+{
+	char devfile[sizeof(int)*3 * 2 + 4];
+	char *sysname;
+	unsigned major_num, minor_num;
+	struct stat st;
+	int r;
+
+	if (strncmp(devname, "/dev/", 5) != 0) {
+		char *cptr;
+
+		cptr = strchr(devname, ':');
+		if (cptr) {
+			/* Colon-separated decimal device number? */
+			*cptr = '\0';
+			major_num = bb_strtou(devname, NULL, 10);
+			if (!errno)
+				minor_num = bb_strtou(cptr + 1, NULL, 10);
+			*cptr = ':';
+			if (!errno)
+				return makedev(major_num, minor_num);
+		} else {
+			/* Hexadecimal device number? */
+			dev_t res = (dev_t) bb_strtoul(devname, NULL, 16);
+			if (!errno)
+				return res;
+		}
+
+		devname = xasprintf("/dev/%s", devname);
+	}
+	/* Now devname is always "/dev/FOO" */
+
+	if (stat(devname, &st) == 0 && S_ISBLK(st.st_mode))
+		return st.st_rdev;
+
+	/* Full blockdevs as well as partitions may be visible
+	 * in /sys/class/block/ even if /dev is not populated.
+	 */
+	sysname = xasprintf("/sys/class/block/%s/dev", devname + 5);
+	r = open_read_close(sysname, devfile, sizeof(devfile) - 1);
+	//free(sysname);
+	if (r > 0) {
+		devfile[r] = '\0';
+		if (sscanf(devfile, "%u:%u", &major_num, &minor_num) == 2) {
+			return makedev(major_num, minor_num);
+		}
+	}
+
+	return (dev_t) 0;
+}
+
+//usage:#define resume_trivial_usage
+//usage:       "BLOCKDEV [OFFSET]"
+//usage:#define resume_full_usage "\n"
+//usage:   "\n""Restore system state from 'suspend-to-disk' data in BLOCKDEV"
+
+int resume_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int resume_main(int argc UNUSED_PARAM, char **argv)
+{
+	unsigned long long ofs;
+	dev_t resume_device;
+	char *s;
+	int fd;
+
+	argv++;
+	if (!argv[0])
+		bb_show_usage();
+
+	resume_device = name_to_dev_t(argv[0]);
+	if (major(resume_device) == 0) {
+		bb_error_msg_and_die("invalid resume device: %s", argv[0]);
+	}
+	ofs = (argv[1] ? xstrtoull(argv[1], 0) : 0);
+
+	fd = xopen("/sys/power/resume", O_WRONLY);
+	s = xasprintf("%u:%u:%llu", major(resume_device), minor(resume_device), ofs);
+
+	xwrite_str(fd, s);
+	/* if write() returns, resume did not succeed */
+
+	return EXIT_FAILURE; /* klibc-utils exits -1 aka 255 */
+}