linux-ext4 - [PATCH 6/7] mke2fs: check for pre-existing file system

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Date:	Sat, 26 Apr 2014 20:00:33 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	Theodore Ts'o <tytso@....edu>
Subject: [PATCH 6/7] mke2fs: check for pre-existing file system

Warn the system administrator if there is an existing file system on
the block device, and give the administrator an opportunity to abort
the mkfs operation.

Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
 misc/mke2fs.c |  4 +++-
 misc/util.c   | 29 +++++++++++++++++++++++++++++
 misc/util.h   |  1 +
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/misc/mke2fs.c b/misc/mke2fs.c
index 799132a..3694ce5 100644
--- a/misc/mke2fs.c
+++ b/misc/mke2fs.c
@@ -1753,7 +1753,9 @@ profile_error:
 	profile_get_integer(profile, "options", "proceed_delay", 0, 5,
 			    &proceed_delay);
 
-	if (!check_plausibility(device_name, CREATE_FILE,
+	/* The isatty() test is so we don't break existing scripts */
+	if (!check_plausibility(device_name, CREATE_FILE |
+				(isatty(0) ? CHECK_FS_EXIST : 0),
 				&is_device) && !force)
 		proceed_question(proceed_delay);
 
diff --git a/misc/util.c b/misc/util.c
index afb0058..be16ebe 100644
--- a/misc/util.c
+++ b/misc/util.c
@@ -113,6 +113,9 @@ int check_plausibility(const char *device, int flags, int *ret_is_dev)
 	int fd, is_dev = 0;
 	ext2fs_struct_stat s;
 	int fl = O_RDONLY;
+	blkid_cache cache = NULL;
+	char *fs_type = NULL;
+	char *fs_label = NULL;
 
 	if (flags & CREATE_FILE)
 		fl |= O_CREAT;
@@ -148,6 +151,32 @@ int check_plausibility(const char *device, int flags, int *ret_is_dev)
 		return 0;
 	}
 
+	if ((flags & CHECK_FS_EXIST) && blkid_get_cache(&cache, NULL) >= 0) {
+		fs_type = blkid_get_tag_value(cache, "TYPE", device);
+		if (fs_type)
+			fs_label = blkid_get_tag_value(cache, "LABEL", device);
+		blkid_put_cache(cache);
+	}
+
+	if (fs_type) {
+		if (fs_label)
+			printf(_("%s contains a %s file system "
+				 "labelled '%s'\n"), device, fs_type, fs_label);
+		else
+			printf(_("%s contains a %s file system\n"), device,
+			       fs_type);
+		free(fs_type);
+		free(fs_label);
+		return 0;
+	}
+
+	/*
+	 * We should eventually replace this with a test for the
+	 * presence of a partition table.  Unfortunately the blkid
+	 * library doesn't test for partition tabels, and checking for
+	 * valid GPT and MBR and possibly others isn't quite trivial.
+	 */
+
 #ifdef HAVE_LINUX_MAJOR_H
 #ifndef MAJOR
 #define MAJOR(dev)	((dev)>>8)
diff --git a/misc/util.h b/misc/util.h
index 9de3fbf..745568e 100644
--- a/misc/util.h
+++ b/misc/util.h
@@ -20,6 +20,7 @@ extern char	*journal_location_string;
  */
 #define CHECK_BLOCK_DEV	0x0001
 #define CREATE_FILE	0x0002
+#define CHECK_FS_EXIST	0x0004
 
 #ifndef HAVE_STRCASECMP
 extern int strcasecmp (char *s1, char *s2);
-- 
1.9.0

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