[PATCH] creating link /dev/root to device / is mounted from

[Matthias Schwarzott <zzam@gentoo.org>]

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Hi there!

Some software (like hal) needs the /dev/root link (as /proc/mounts can contain 
it).

The attached patch contains one program which compares the major/minor number 
supplied to it on the command-line with the numbers of the device / is 
located on.
It is used with this rule (see 60-root_link.rules):
SUBSYSTEM=="block", PROGRAM=="blockdev_is_root $major $minor", SYMLINK+="root"

The patch also adds the rule to the gentoo rules file.

Matthias
-- 
Matthias Schwarzott (zzam)

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diff --git a/etc/udev/gentoo/50-udev.rules b/etc/udev/gentoo/50-udev.rules
index 2887553..7e0acec 100644
--- a/etc/udev/gentoo/50-udev.rules
+++ b/etc/udev/gentoo/50-udev.rules
@@ -36,6 +36,9 @@ KERNEL=="ircomm*",	NAME="%k", GROUP="uucp", MODE="0660"
 # all block devices
 SUBSYSTEM=="block", GROUP="disk"
 
+# create link /dev/root to the blockdevice / is mounted from
+SUBSYSTEM=="block", PROGRAM=="blockdev_is_root $major $minor", SYMLINK+="root"
+
 # cdrom symlinks and other good cdrom naming
 KERNEL=="sr[0-9]*|hd[a-z]|pcd[0-9]*", ACTION=="add", IMPORT{program}="cdrom_id --export $tempnode"
 ENV{ID_CDROM}=="?*", GROUP="cdrom"
diff --git a/extras/root_link/60-root_link.rules b/extras/root_link/60-root_link.rules
new file mode 100644
index 0000000..2175876
--- /dev/null
+++ b/extras/root_link/60-root_link.rules
@@ -0,0 +1,3 @@
+# create link /dev/root to the blockdevice / is mounted from
+
+SUBSYSTEM=="block", PROGRAM=="blockdev_is_root $major $minor", SYMLINK+="root"
diff --git a/extras/root_link/Makefile b/extras/root_link/Makefile
new file mode 100644
index 0000000..2420df5
--- /dev/null
+++ b/extras/root_link/Makefile
@@ -0,0 +1,69 @@
+# Makefile for udev extra invoked from the udev main Makefile
+#
+# Copyright (C) 2004-2005 Kay Sievers <kay.sievers@vrfy.org>
+#
+# Released under the GNU General Public License, version 2.
+#
+
+PROG = blockdev_is_root
+OBJ =
+HEADERS =
+GEN_HEADERS =
+MAN_PAGES =
+
+prefix =
+etcdir =	${prefix}/etc
+sbindir =	${prefix}/sbin
+usrbindir =	${prefix}/usr/bin
+usrsbindir =	${prefix}/usr/sbin
+libudevdir =	${prefix}/lib/udev
+mandir =	${prefix}/usr/share/man
+configdir =	${etcdir}/udev/
+
+INSTALL = install -c
+INSTALL_PROGRAM = ${INSTALL}
+INSTALL_DATA  = ${INSTALL} -m 644
+INSTALL_SCRIPT = ${INSTALL}
+
+all: $(PROG) $(MAN_PAGES)
+.PHONY: all
+.DEFAULT: all
+
+%.o: %.c $(GEN_HEADERS)
+	$(E) "  CC      " $@
+	$(Q) $(CC) -c $(CFLAGS) $< -o $@
+
+$(PROG): %: $(HEADERS) %.o $(OBJS)
+	$(E) "  LD      " $@
+	$(Q) $(LD) $(LDFLAGS) $@.o $(OBJS) -o $@ $(LIBUDEV) $(LIB_OBJS)
+
+# man pages
+%.8: %.xml
+	$(E) "  XMLTO   " $@
+	$(Q) xmlto man $?
+.PRECIOUS: %.8
+
+clean:
+	$(E) "  CLEAN   "
+	$(Q) rm -f $(PROG) $(OBJS) $(GEN_HEADERS)
+.PHONY: clean
+
+install-bin: all
+	$(INSTALL_PROGRAM) -D $(PROG) $(DESTDIR)$(libudevdir)/$(PROG)
+.PHONY: install-bin
+
+uninstall-bin:
+	- rm $(DESTDIR)$(libudevdir)/$(PROG)
+.PHONY: uninstall-bin
+
+install-man:
+	@echo "Please create a man page for this tool."
+.PHONY: install-man
+
+uninstall-man:
+	@echo "Please create a man page for this tool."
+.PHONY: uninstall-man
+
+install-config:
+	@echo "no config file to install"
+.PHONY: install-config
diff --git a/extras/root_link/blockdev_is_root.c b/extras/root_link/blockdev_is_root.c
new file mode 100644
index 0000000..f873108
--- /dev/null
+++ b/extras/root_link/blockdev_is_root.c
@@ -0,0 +1,73 @@
+/*
+ * blockdev_is_root - compare major/minor from cmdline to the device / is on
+ *
+ * Copyright (C) 2007 Matthias Schwarzott <zzam@gentoo.org>
+ *
+ *      This program is free software; you can redistribute it and/or modify it
+ *      under the terms of the GNU General Public License as published by the
+ *      Free Software Foundation version 2 of the License.
+ */
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+// Getting major/minor
+#include <sys/sysmacros.h>
+
+void usage(void);
+
+void usage(void)
+{
+	fprintf(stderr, "Usage:\n");
+	fprintf(stderr, "  blockdev_is_root MAJOR MINOR\n");
+	fprintf(stderr, "  Exit code will be 0 if device is the one \"/\" is mounted from.\n");
+}
+
+int main(int argc, char **argv)
+{
+	struct stat stat_buf;
+	unsigned int dev_major=0, dev_minor=0;
+	dev_t root_dev, dev_dev;
+
+	if (argc < 3) {
+		usage();
+		return EXIT_FAILURE;
+	}
+
+	if (argv[1])
+		dev_major=strtol(argv[1], NULL, 10);
+	else
+		return EXIT_FAILURE;
+
+	if (dev_major == 0) {
+		fprintf(stderr, "MAJOR == 0\n");
+		return EXIT_FAILURE;
+	}
+
+	if (argv[2])
+		dev_minor=strtol(argv[2], NULL, 10);
+	else
+		return EXIT_FAILURE;
+
+	dev_dev = gnu_dev_makedev(dev_major, dev_minor);
+
+	if (stat("/", &stat_buf) < 0) {
+		perror("stat");
+		return EXIT_FAILURE;
+	}
+
+	root_dev = stat_buf.st_dev;
+
+	// printf("ROOT: %lld \n", (long long) root_dev);
+	// printf("DEV:  %lld \n", (long long) dev_dev);
+
+	if (dev_dev == root_dev)
+		return EXIT_SUCCESS;
+
+	return EXIT_FAILURE;
+}
+

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