check if partition is mounted before mkfs

This saves from the blunder of formatting a live mounted filesystem.
This can be extended to get the mount flags of the filesystem
mounted.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@gmail.com>

mkfs.c

@@ -197,6 +197,15 @@ int main(int ac, char **av)
 		print_usage();
 
 	file = av[optind++];
+	ret = check_mounted(file);
+	if (ret < 0) {
+		fprintf(stderr, "error checking %s mount status\n", file);
+		exit(1);
+	}
+	if (ret == 1) {
+		fprintf(stderr, "%s is mounted\n", file);
+		exit(1);
+	}
 	ac--;
 	fd = open(file, O_RDWR);
 	if (fd < 0) {
@@ -241,6 +250,16 @@ int main(int ac, char **av)
 	zero_end = 1;
 	while(ac-- > 0) {
 		file = av[optind++];
+		ret = check_mounted(file);
+		if (ret < 0) {
+			fprintf(stderr, "error checking %s mount status\n",
+				file);
+			exit(1);
+		}
+		if (ret == 1) {
+			fprintf(stderr, "%s is mounted\n", file);
+			exit(1);
+		}
 		fd = open(file, O_RDWR);
 		if (fd < 0) {
 			fprintf(stderr, "unable to open %s\n", file);

utils.c

@@ -30,6 +30,7 @@
 #include <dirent.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <mntent.h>
 #include "kerncompat.h"
 #include "radix-tree.h"
 #include "ctree.h"
@@ -525,6 +526,58 @@ error:
 	return ret;
 }
 
+/*
+ * returns 1 if the device was mounted, < 0 on error or 0 if everything
+ * is safe to continue.  TODO, this should also scan multi-device filesystems
+ */
+int check_mounted(char *file)
+{
+	struct mntent *mnt;
+	struct stat st_buf;
+	dev_t file_dev = 0;
+	dev_t file_rdev = 0;
+	ino_t file_ino = 0;
+	FILE *f;
+	int ret = 0;
+
+	if ((f = setmntent ("/proc/mounts", "r")) == NULL)
+		return -errno;
+
+	if (stat(file, &st_buf) < 0) {
+		return -errno;
+	} else {
+		if (S_ISBLK(st_buf.st_mode)) {
+			file_rdev = st_buf.st_rdev;
+		} else {
+			file_dev = st_buf.st_dev;
+			file_ino = st_buf.st_ino;
+		}
+	}
+
+	while ((mnt = getmntent (f)) != NULL) {
+		if (strcmp(file, mnt->mnt_fsname) == 0)
+			break;
+
+		if (stat(mnt->mnt_fsname, &st_buf) == 0) {
+			if (S_ISBLK(st_buf.st_mode)) {
+				if (file_rdev && (file_rdev == st_buf.st_rdev))
+					break;
+			} else if (file_dev && ((file_dev == st_buf.st_dev) &&
+						(file_ino == st_buf.st_ino))) {
+					break;
+			}
+		}
+	}
+
+	if (mnt) {
+		/* found an entry in mnt table */
+		ret = 1;
+	}
+
+	endmntent (f);
+	return ret;
+}
+
 struct pending_dir {
 	struct list_head list;
 	char name[256];

utils.h

@@ -35,4 +35,5 @@ int btrfs_scan_for_fsid(struct btrfs_fs_devices *fs_devices, u64 total_devs,
 			int run_ioctls);
 int btrfs_register_one_device(char *fname);
 int btrfs_scan_one_dir(char *dirname, int run_ioctl);
+int check_mounted(char *devicename);
 #endif