[PATCH RFC] vfs: add mount umount logs

[Anand Jain <anand.jain@oracle.com>]

By looking at the logs we should be able to know when was the FS
mounted and unmounted and the options used, so to help forensic
investigations.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
You may want to know that, during boot and shutdown this
adds roughly 25 lines more logs depending on the config, and it
logs even for non block device FS, such as proc, sysfs ..etc.
And blockdev FS only check will eliminate overlay as well, which
is kind of defeats the purpose.
Further, just to highlight if your test script involves mount and
umount, which probably all of fstests does, it will add logs when
FS is mounted and umounted.
Still IMO, these logs are useful for the end purpose as mentioned
above. Its for your feedback. Thanks.

 fs/namespace.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index b3b115bd4e1e..78375b6f8330 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1686,6 +1686,8 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
 	struct mount *mnt;
 	int retval;
 	int lookup_flags = 0;
+	struct super_block *sb;
+	char umntlog[256] = {0};
 
 	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
 		return -EINVAL;
@@ -1711,7 +1713,15 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
 	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
 		goto dput_and_out;
 
+	sb = mnt->mnt.mnt_sb;
+	snprintf(umntlog, sizeof(umntlog), "umount %s dev:%s flags:%d",
+		sb->s_type->name, sb->s_id, flags);
+
 	retval = do_umount(mnt, flags);
+
+	if (!retval)
+		printk(KERN_NOTICE "%s\n", umntlog);
+
 dput_and_out:
 	/* we mustn't call path_put() as that would clear mnt_expiry_mark */
 	dput(path.dentry);
@@ -2833,6 +2843,11 @@ long do_mount(const char *dev_name, const char __user *dir_name,
 	else
 		retval = do_new_mount(&path, type_page, flags, mnt_flags,
 				      dev_name, data_page);
+
+	if (!retval)
+		printk(KERN_NOTICE "mount %s dev:%s dir:%pd flags:0x%lX opt:%s\n",
+			type_page, dev_name, path.dentry, flags, (char *)data_page);
+
 dput_out:
 	path_put(&path);
 	return retval;
-- 
2.10.0