libmount: improve conversion from root= to the devname

Currently the code supports /dev/name or PARTUUID= only. We also
need to support 'maj:min' and 'hexhex' notations.

Reported-by: George Spelvin <linux@horizon.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

3 files changed, 122 insertions, 9 deletions

diff --git a/libmount/src/mountP.h b/libmount/src/mountP.h
index 46919f2a0..2baab55de 100644
--- a/libmount/src/mountP.h
+++ b/libmount/src/mountP.h
@@ -101,6 +101,7 @@ extern int mnt_get_filesystems(char ***filesystems, const char *pattern);
 extern void mnt_free_filesystems(char **filesystems);
 
 extern char *mnt_get_kernel_cmdline_option(const char *name);
+extern int mnt_guess_system_root(dev_t devno, struct libmnt_cache *cache, char **path);
 extern int mnt_stat_mountpoint(const char *target, struct stat *st);
 
 /* tab.c */
diff --git a/libmount/src/tab_parse.c b/libmount/src/tab_parse.c
index cee700816..23076bfc0 100644
--- a/libmount/src/tab_parse.c
+++ b/libmount/src/tab_parse.c
@@ -580,19 +580,16 @@ static int kernel_fs_postparse(struct libmnt_table *tb,
 	 * Convert obscure /dev/root to something more usable
 	 */
 	if (src && strcmp(src, "/dev/root") == 0) {
-		char *spec = mnt_get_kernel_cmdline_option("root=");
 		char *real = NULL;
 
-		DBG(TAB, ul_debugobj(tb, "root FS: %s", spec));
-		if (spec)
-			real = mnt_resolve_spec(spec, tb->cache);
-		if (real) {
+		rc = mnt_guess_system_root(fs->devno, tb->cache, &real);
+		if (rc < 0)
+			return rc;
+
+		if (rc == 0 && real) {
 			DBG(TAB, ul_debugobj(tb, "canonical root FS: %s", real));
-			rc = mnt_fs_set_source(fs, real);
-			if (!tb->cache)
-				free(real);
+			rc = __mnt_fs_set_source_ptr(fs, real);
 		}
-		free(spec);
 	}
 
 	return rc;
diff --git a/libmount/src/utils.c b/libmount/src/utils.c
index 5a62879a4..0fcc1d070 100644
--- a/libmount/src/utils.c
+++ b/libmount/src/utils.c
@@ -25,6 +25,7 @@
 #include "match.h"
 #include "fileutils.h"
 #include "statfs_magic.h"
+#include "sysfs.h"
 
 int append_string(char **a, const char *b)
 {
@@ -1095,6 +1096,92 @@ char *mnt_get_kernel_cmdline_option(const char *name)
 	return res;
 }
 
+/*
+ * Converts @devno to the real device name if devno major number is greater
+ * than zero, otherwise use root= kernel cmdline option to get device name.
+ *
+ * The function uses /sys to convert devno to device name.
+ *
+ * Returns: 0 = success, 1 = not found, <0 = error
+ */
+int mnt_guess_system_root(dev_t devno, struct libmnt_cache *cache, char **path)
+{
+	char buf[PATH_MAX];
+	char *dev = NULL, *spec;
+	unsigned int x, y;
+	int allocated = 0;
+
+	assert(path);
+
+	DBG(UTILS, ul_debug("guessing system root [devno %u:%u]", major(devno), minor(devno)));
+
+	/* The pseudo-fs, net-fs or btrfs devno is useless, otherwise it
+	 * usually matches with the source device, let's try to use it.
+	 */
+	if (major(devno) > 0) {
+		dev = sysfs_devno_to_devpath(devno, buf, sizeof(buf));
+		if (dev) {
+			DBG(UTILS, ul_debug("  devno converted to %s", dev));
+			goto done;
+		}
+	}
+
+	/* Let's try to use root= kernel command line option
+	 */
+	spec = mnt_get_kernel_cmdline_option("root=");
+	if (!spec)
+		goto done;
+
+	/* maj:min notation */
+	if (sscanf(spec, "%u:%u", &x, &y) == 2) {
+		dev = sysfs_devno_to_devpath(makedev(x, y), buf, sizeof(buf));
+		if (dev) {
+			DBG(UTILS, ul_debug("  root=%s converted to %s", spec, dev));
+			goto done;
+		}
+
+	/* hexhex notation */
+	} else if (isxdigit_string(spec)) {
+		char *end = NULL;
+		uint32_t n;
+
+		errno = 0;
+		n = strtoul(spec, &end, 16);
+
+		if (errno || spec == end || (end && *end))
+			DBG(UTILS, ul_debug("  failed to parse root='%s'", spec));
+		else {
+			/* kernel new_decode_dev() */
+			x = (n & 0xfff00) >> 8;
+			y = (n & 0xff) | ((n >> 12) & 0xfff00);
+			dev = sysfs_devno_to_devpath(makedev(x, y), buf, sizeof(buf));
+			if (dev) {
+				DBG(UTILS, ul_debug("  root=%s converted to %s", spec, dev));
+				goto done;
+			}
+		}
+
+	/* devname or PARTUUID= etc. */
+	} else {
+		DBG(UTILS, ul_debug("  converting root='%s'", spec));
+
+		dev = mnt_resolve_spec(spec, cache);
+		if (dev && !cache)
+			allocated = 1;
+	}
+	free(spec);
+done:
+	if (dev) {
+		*path = allocated ? dev : strdup(dev);
+		if (!path)
+			return -ENOMEM;
+		return 0;
+	}
+
+	return 1;
+}
+
+
 #ifdef TEST_PROGRAM
 static int test_match_fstype(struct libmnt_test *ts, int argc, char *argv[])
 {
@@ -1207,6 +1294,33 @@ static int test_kernel_cmdline(struct libmnt_test *ts, int argc, char *argv[])
 	return 0;
 }
 
+
+static int test_guess_root(struct libmnt_test *ts, int argc, char *argv[])
+{
+	int rc;
+	char *real;
+	dev_t devno = 0;
+
+	if (argc) {
+		unsigned int x, y;
+
+		if (sscanf(argv[1], "%u:%u", &x, &y) != 2)
+			return -EINVAL;
+		devno = makedev(x, y);
+	}
+
+	rc = mnt_guess_system_root(devno, NULL, &real);
+	if (rc < 0)
+		return rc;
+	if (rc == 1)
+		fputs("not found\n", stdout);
+	else {
+		printf("%s\n", real);
+		free(real);
+	}
+	return 0;
+}
+
 static int test_mkdir(struct libmnt_test *ts, int argc, char *argv[])
 {
 	int rc;
@@ -1247,6 +1361,7 @@ int main(int argc, char *argv[])
 	{ "--mountpoint",    test_mountpoint,      "<path>" },
 	{ "--cd-parent",     test_chdir,           "<path>" },
 	{ "--kernel-cmdline",test_kernel_cmdline,  "<option> | <option>=" },
+	{ "--guess-root",    test_guess_root,      "[<maj:min>]" },
 	{ "--mkdir",         test_mkdir,           "<path>" },
 	{ "--statfs-type",   test_statfs_type,     "<path>" },