libfstools: gather mountpoints from /proc/self/mountinfo

This allows identifying /dev/root by its major:minor number which
are part of /proc/self/mountinfo but aren't contained in /proc/mounts.
Also fix jffs2reset when using an ext4 overlay by adding it to the
list of filesystems allowed if the root_only parameter of
find_mount_point is set.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

1 files changed, 120 insertions, 24 deletions

diff --git a/libfstools/find.c b/libfstools/find.c
index 72a2b4c..52bc51f 100644
--- a/libfstools/find.c
+++ b/libfstools/find.c
@@ -14,6 +14,7 @@
 #include <errno.h>
 #include <stdio.h>
 #include <string.h>
+#include <sys/stat.h>
 
 #include "libfstools.h"
 
@@ -76,40 +77,135 @@ find_mount(char *mp)
 	return point;
 }
 
+/*
+ * Match filesystem type against a bunch of valid types
+ *
+ * jffs2reset may ask if the filesystem type is actually ready for use
+ * with overlayfs before wiping it...
+ */
+static int fs_rootfs_only(char *fstype)
+{
+	if (strncmp(fstype, "ext4", 4) &&
+	    strncmp(fstype, "f2fs", 4) &&
+	    strncmp(fstype, "jffs2", 5) &&
+	    strncmp(fstype, "ubifs", 5)) {
+		ULOG_ERR("block is mounted with wrong fs\n");
+		return 1;
+	}
+	return 0;
+}
+
+/*
+ * Check if a given device is mounted and return its mountpoint
+ */
 char*
 find_mount_point(char *block, int root_only)
 {
-	FILE *fp = fopen("/proc/mounts", "r");
+	FILE *fp = fopen("/proc/self/mountinfo", "r");
 	static char line[256];
 	int len = strlen(block);
-	char *point = NULL;
+	char *point = NULL, *pos, *tmp, *cpoint, *devname, *fstype;
+	struct stat s;
+	int rstat;
+	unsigned int minor, major;
 
-	if(!fp)
+	if (!fp)
 		return NULL;
 
+	rstat = stat(block, &s);
+
 	while (fgets(line, sizeof(line), fp)) {
-		if (!strncmp(line, block, len)) {
-			char *p = &line[len + 1];
-			char *t = strstr(p, " ");
-
-			if (!t) {
-				fclose(fp);
-				return NULL;
-			}
-
-			*t = '\0';
-			t++;
-
-			if (root_only &&
-			    strncmp(t, "f2fs", 4) &&
-			    strncmp(t, "jffs2", 5) &&
-			    strncmp(t, "ubifs", 5)) {
-				fclose(fp);
-				ULOG_ERR("block is mounted with wrong fs\n");
-				return NULL;
-			}
-			point = p;
+		/* skip first two columns */
+		pos = strchr(line, ' ');
+		if (!pos)
+			continue;
+
+		pos = strchr(pos + 1, ' ');
+		if (!pos)
+			continue;
+
+		/* extract block device major:minor */
+		tmp = ++pos;
+		pos = strchr(pos, ':');
+		if (!pos)
+			continue;
+
+		*pos = '\0';
+		major = atoi(tmp);
+
+		tmp = ++pos;
+		pos = strchr(pos, ' ');
+		if (!pos)
+			continue;
+
+		*pos = '\0';
+		minor = atoi(tmp);
+
+		/* skip another column */
+		pos = strchr(pos + 1, ' ');
+		if (!pos)
+			continue;
+
+		/* get mountpoint */
+		tmp = ++pos;
+		pos = strchr(pos, ' ');
+		if (!pos)
+			continue;
+
+		*pos = '\0';
+		cpoint = tmp;
+
+		/* skip another two columns */
+		pos = strchr(pos + 1, ' ');
+		if (!pos)
+			continue;
+
+		pos = strchr(pos + 1, ' ');
+		if (!pos)
+			continue;
+
+		/* get fstype */
+		tmp = ++pos;
+		pos = strchr(pos, ' ');
+		if (!pos)
+			continue;
+
+		*pos = '\0';
+		fstype = tmp;
+
+		/* get device name */
+		tmp = ++pos;
+		pos = strchr(pos, ' ');
+		if (!pos)
+			continue;
+
+		*pos = '\0';
+		devname = tmp;
+
+		/* if device name matches */
+		if (!strncmp(block, devname, len)) {
+			if (root_only && fs_rootfs_only(fstype))
+				break;
+
+			/* found, return mountpoint */
+			point = strdup(cpoint);
+			break;
+		}
+
+		/* last chance: check if major:minor of block device match */
+		if (rstat)
+			continue;
+
+		if (!S_ISBLK(s.st_mode))
+			continue;
+
+		if (major == major(s.st_rdev) &&
+		    minor == minor(s.st_rdev)) {
+			if (root_only && fs_rootfs_only(fstype))
+				break;
 
+			/* found, return mountpoint */
+			point = strdup(cpoint);
 			break;
 		}
 	}